- A.P.E.S. Database

A Field Survey Manual for Vertebrates
Edited by Glyn Davies
Earthwatch supports field research projects in over 40 countries around
the world, in a wide range of disciplines and habitats. The organisation has
supported research in African tropical forests for over 20 years, and accepts
applications for funding from researchers across the continent.
Earthwatch Europe runs a professional development programme
designed to build the capacity of African institutions working to conserve
biodiversity. Our African Fellowship Programme places African conservationists,
scientists and NGO workers on field research projects relevant to their
professional lives. The programme provides training in an African context;
through the unique experience of practical participation on a project in another
African country, and working in an international team with other African
conservation professionals from across the continent.
Publication of this manual has been made possible through a
generous donation from Rio Tinto plc.
African Forest Biodiversity:
a field survey manual for
vertebrates
Editor Glyn Davies
Assistant Editor Michael Hoffmann
Authors
Leon Bennun*
Department of Ornithology
National Museums of Kenya
P O Box 40658
Nairobi
Kenya
Glyn Davies
Zoological Society of London
Regents Park
London NW1 4RY
UK
Kim Howell
Department of Zoology and Marine Biology
University of Dar es Salaam
P O Box 35064
Dar es Salaam
Tanzania
Helen Newing
Durrell Institute of Conservation and Ecology
University of Kent at Canterbury
Canterbury
Kent CT2 7NS
UK
Matthew Linkie
Durrell Institute of Conservation and Ecology
University of Kent at Canterbury
Canterbury
Kent CT2 7NS
UK
Illustrations by
John Clarke
*Current Address: Birdlife International, Wellbrook Court, Girton Road, Cambridge, CB3 0NA, UK
Published in the UK in 2002 by Earthwatch Europe.
ISBN 0-9538179-4-6
Publisher’s reference: 141-04-02
© Copyright Earthwatch Institute (Europe) and contributors 2002.
All rights reserved. The use and reproduction of any part of this publication is welcomed for noncommercial purposes only, provided that the source is acknowledged.
This publication was funded by the EC Tropical Forests budget line. The authors are solely
responsible for all opinions expressed in this document, which do not necessarily reflect those of
the European Union.
Printed by Seacourt Press, who hold ISO 14001 and EMAS environmental certifications, using
waterless printing and vegetable-based inks on chlorine free part-recycled paper.
®
Earthwatch Institute (Europe) is a self-governing and self-financing charity (Registered Number
327017) operating under English law with an independent Board of Trustees, and is affiliated with a
global organization led by Earthwatch Institute in the US from and through which Earthwatch
Institute (Europe) obtains a variety of goods and services including the right to use the Earthwatch
name and access to the Earthwatch international program of field projects.
Acknowledgements
This manual has benefitted from discussions and the reports from two
forest survey workshops: Kakamega, Kenya (1995) and Limbe, Cameroon
(1996). This restructured and rewritten document has been improved with
helpful comments and advice from: Tom Butynski, Tim Davenport, Rob and
Cheryl Fimbel, Frank Hawkins, Dwight Larsen, Martyn Murray, John Oates,
Andy Plumptre, and Justina Ray. I am grateful to all of them for their time and
assistance. I am indebted to all the authors, who have stuck at this through
thick and thin, and to John Clarke whose plates have greatly enhanced the
visual image of the document.
Mike Hoffmann came to our aid with the final compilation and editing,
and Sylvia Howe assisted with the design, layout and proof reading. Julian
Laird (Earthwatch Europe) has steadfastly supported the production of this
document following a visit to Limbe in 1997, and we acknowledge the financial
support of the EC Tropical Forests budget line and Rio Tinto plc.
Glyn Davies
Editor
Main cover photograph by Glyn Davies.
Side bar photographs by Glyn Davies, except bottom photograph
courtesy of Marcus Rowcliffe.
Contents
1. Introduction
1.1
1.2
1.3
Background
Scope of the Manual
Structure and content
1
2
3
2. Forest Surveys
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
What is forest biodiversity?
Forest management
Research into forest biodiversity
Ethical and legal standards
Preparations
A note on market surveys
and questionnaires/ interviews
Health and safety
References
5
7
9
11
11
14
15
16
3. Amphibians and reptiles: herptiles
3.1
3.2
3.3
3.4
3.5
3.6
3.7
Biology
Management issues
Methods
3.3.1 General surveys
3.3.2 Drift fences and pitfall traps
3.3.3 Canopy walkway trap
3.3.4 Snake trapping
3.3.5 Capture, mark, recapture
3.3.6 Forest litter plots
3.3.7 Time-constrained searches
3.3.8 Transect counts
3.3.9 Territory mapping
3.3.10 Sound recording surveys
Specimen handling
Health and safety
Conclusions
References
17
18
19
21
23
27
29
31
31
33
34
34
35
36
37
38
39
4. Small mammals: bats, rodents
and insectivores
4.1
4.2
4.3
4.4
4.5
4.6
4.7
Biology
Management issues
Methods
4.3.1 General surveys
4.3.2 Bat roost surveys
4.3.3 Live-trapping: rodents and insectivores
4.3.4 Live-trapping: bats
4.3.5 Capture, mark, recapture
4.3.6 Removal or dead-trapping
Specimen handling
Health and safety
Conclusions
References
45
47
48
49
49
50
54
58
59
60
64
64
65
5. Large and medium-sized mammals
5.1
5.2
5.3
5.4
5.5
Biology
Management issues
Methods
5.3.1 Hunters’ calls, attractants and observation points
5.3.2 Net drives
5.3.3 Survey walks: reconnaissance surveys
and transect
5.3.4 Indirect methods
A. Dung counts
B. Track (footprint) surveys
C. Photo-recording
Conclusions
References
69
70
72
73
75
77
82
82
86
90
92
92
6. Primates
6.1
6.2
6.3
6.4
6.5
Biology
Management issues
Methods
6.3.1 Distribution surveys
6.3.2 Line transects
A. Animal sightings
B. Nest counts
C. Mapping calls
6.3.3 Sweep surveys
Conclusions
References
99
102
104
105
106
107
110
111
114
116
116
7. Birds
7.1
7.2
7.3
7.4
7.5
7.6
7.7
Biology
Management issues
Methods
7.3.1 General surveys
7.3.2 Timed species-counts (TSCs)
7.3.3 MacKinnon lists and related methods
7.3.4 Timed transects (TTs)
7.3.5 Fixed-width transect counts
7.3.6 Fixed-width point counts
7.3.7 Distance sampling
7.3.8 Mist netting and ringing
7.3.9 Sound recording
7.3.10 Territory mapping
7.3.11 Special considerations
Specimen handling
Health and safety
Conclusions
References
121
124
126
130
131
134
136
136
138
140
141
147
149
149
151
152
152
154
1.
Introduction
Glyn Davies
1.1
Background
This manual is the product of many years of forest survey experience,
and is based upon discussions between field workers about ways that surveys
can be improved and standardised.
The first steps towards producing this manual were taken at the 4th East
African Regional Database workshop, held in Kampala in August 1993, when
participants expressed an urgent need for guidelines that would allow standardisation of field methods for forest biodiversity surveys. In response, the
regional Global Environment Facility (GEF) Project (Institutional Support for the
Protection of East African Biodiversity) agreed to fund a training workshop, as
part of its Conservation and Management of Closed Forests programme. This
workshop was held in Kakamega Forest Reserve and Mount Elgon National
Park, Kenya in November 1994, and led to the production of a workshop
report/training manual titled Guidelines for Forest Biodiversity Inventories
(1995:UHNO/RAF/006/GEF).
Two years later, at another GEF-supported workshop in Limbe Botanic
Garden, Cameroon, many of the same forest survey issues were discussed in
the context of the Central African region (March 1996). Another workshop
report was produced at this meeting: Protocols for Biological Surveys in
Cameroonian Forests.
1
Although both workshop reports served their immediate purposes of
recording conclusions of survey experience, there were frequent requests
(often from isolated project managers and field staff) for copies of the documents long after the workshops had finished. Because the obvious conclusion
from both of these documents was that many of the survey methods could be
applied in the field in both forest regions, the requests prompted the current
collaborative effort to produce a forest survey field manual that would be
distributed widely.
1.2
Scope of the manual
This manual concentrates only on forest vertebrates, excluding fish.
The Kakamega and Limbe workshops focused on surveys of a much wider
spectrum of forest fauna and flora, and attention was also given to socio-economic survey methods. It was beyond the resources of those involved in the
production of this manual to cover this full range of subjects, but it is hoped
that future survey manuals can be produced to cover them.
Two excellent series that describe survey methods for single taxonomic
groups are the comprehensive Measuring and Monitoring Biodiversity series,
produced by the Smithsonian Institution (Washington, USA), and the lessdetailed Expeditions Field Techniques series by the Royal Geographical
Society (London, UK). Furthermore, an excellent technical handbook
Conservation Research in African Rainforests (White & Edwards, 2000) has
recently been published, which focuses on vegetation and large mammal
surveys in central Africa.
This manual differs in that it moves away from the single taxonomic
group approach, and considers the full range of vertebrates found in African
forests. By so doing, we hope to raise awareness about the possibilities of carrying out surveys of several taxonomic groups at a given forest site. This does
not preclude surveys focusing on particuar groups; but does encourage data
gathering on other species (see general surveys in each chapter).
The target audience for the manual comprises four main groups:
●
people carrying out short reconnaissance surveys and expeditions;
●
undergraduate and graduate students carrying out project
and thesis work;
●
research departments of forest, wildlife and national parks
departments;
●
forest and wildlife managers and technicians with responsibility
for monitoring biodiversity.
2
Enlightened forest management requires information about a broad
range of species, and time is too short, and resources too limited, for all forest
areas to be considered by separate specialist survey teams. By explaining the
range of methods available to gather information on biodiversity issues, forest
managers and planners will be aware of how information is gathered, and so
feel better equipped to include biodiversity in their work.
The primary aim of the manual, therefore, is to provide an overview of
the methods that can be used to gather information needed for effective management of African forests, which takes full account of all vertebrates as a
component of forest ecosystem biodiversity.
An important extension of this aim is to encourage surveyors and
researchers to use standardised methods so that survey results can be used to
monitor change over time, whether changes are positive as a result of management interventions or negative as a result of unsustainable use or clearance.
Long-term monitoring usually involves different surveyors, as people change
jobs or move, and each set of new observers/surveyors should use the same
methods if the results are to be comparable. While focusing attention on this
need for standardised methods, it is understood that methods continue to be
improved, and different forests, survey team resources, and management
questions will all require adaptation of the standard techniques.
Finally, the manual is intended as a field companion, and as a training
tool for students, at college and university, and in forest and wildlife services.
However, this manual is not a field identification guide and the relevant identification guides will be needed.
1.3
Structure and content
Chapter 2, Forest Surveys, gives a brief introduction to forest biodiversity
and management, and the need for research as a tool in managing forest biodiversity. In addition, it includes introductory notes on ethical and legal standards, preparations for carrying out surveys, and notes on health and safety.
Chapters 3 to 7 cover the survey methods according to each respective
group of animals. Each chapter includes sections on the biology and management issues of the relevant group, the various survey methods, followed by
pointers on specimen handling and, in some cases, additional notes on health
and safety. Each chapter concludes with a list of references. To ease reference, the survey methods discussed in these chapters have been organised to
follow generally similar headings giving: additional/special equipment or personnel required (see 2.5); site selection (where pertinent); procedure;
processes of recording; data analysis; and an assessment of the advantages
and limitations of the methods. To avoid unnecessary repetition, certain
3
sections have not been duplicated in each chapter, in which case the reader
will be referred to the relevant section in another chapter. However, readers are
advised to read the introductory sections of all chapters because different
authors have stressed different issues – all of which are important whatever
species group is being surveyed.
The manual can be carried into the field to guide survey work, in order to
ensure that the right information is gathered for subsequent analysis and report
writing. It is beyond the scope of this manual to provide details of the statistical
tests or analyses required to analyse and interpret field survey results
accurately. Instead, such texts are referenced in the chapters (including the
Smithsonian series and White & Edwards (2000)), and these should be consulted in conjunction with this manual. Sample survey forms, which can be
photocopied for use in the field, are included at the back of each chapter.
Given the background, some chapters put stronger emphasis on forests
in eastern Africa, and others on western and central Africa. However, the survey methods described, and the principles that need to be followed, apply in all
forest surveys in Africa, in Madagascar, and, indeed, even on other continents.
4
2.
Forest Surveys
Glyn Davies
2.1
What is forest diversity?
Biodiversity is the wealth of all life on earth, which can be considered at
three inter-linked levels: genetic, species and ecosystem (see Box 1).
Biodiversity is ‘... the variability among living organisms from all
sources, including, inter alia, terrestrial, marine and other aquatic ecosystems
and the ecological complexes of which they are part; this includes diversity
within species, between species and of ecosystems.’ (Article 2, Convention
on Biological Diversity, 1992).
Forest biodiversity can also be considered in terms of composition,
structure and function, and generally is characterised by:
●
very high species richness – 50% of all terrestrial species in the
world are found in rain forests;
●
multi-layered structure, with giant emergent trees, forest floor
herbs, epiphytic herbs and woody lianas, and a correspondingly
dark understorey;
●
often infertile soils and rapid recycling of plant and soil nutrients;
●
long timescales over which patterns of regeneration and
reproduction take place.
5
Box 1: Levels of biodiversity
●
●
●
Genetic biodiversity refers to the frequency and variety of genes
and/or genomes within, and between, populations of the same
species, and the information contained within these genes provides
the basis for evolution through adaptation. Examples of genetic biodiversity are reflected in the different coat colours of mona monkeys,
Cercopithecus mona, or in the yields of a plantation tree species.
Species biodiversity refers to the number and abundance of species
in an area, and the extent to which species differ in their genetic
make-up. It incorporates characteristics such as taxonomic uniqueness, size and structure, population dynamics, reproductive cycles and
behaviour patterns.
Ecosystem biodiversity is reflected in the definition of an ecosystem:
‘...a dynamic complex of plant, animal and micro-organism communities and their non-living environment, interacting as a functional unit.’
(Convention on Biological Diversity). The interplay between species
includes pollination, predation, parasitism and symbiosis, while the
interaction between species and their non-living environment includes
soil formation, photosynthesis etc. Ecosystems and human culture
have influenced each other over the millennia, giving rise to productive
landscapes that combine biological and cultural diversity.
Measuring forest biodiversity must therefore take account of these
characteristics, and pay attention to different species’ qualities, sometimes
termed ‘bioqualities’ – are they common, forest-dependent, rare, insectivorous,
medicinal plants, marketable timber, and so on? With such a range of features
to consider, and a lack of detailed ecological information on many forest
species, it is inevitable that surveys have often focused on a number of indicator species in an area as a first approximation of forest biodiversity (Noss,
1990). But this raises the question of which species to select for surveys.
One obvious approach is to focus on one, or a set of, key species in
relation to a particular management question, such as over-exploitation of a
medicinal plant, or the unsustainable trapping of large mammals. By monitoring these ‘threatened’ species, and ensuring that their use is managed in a
sustainable way, other forest plant and animal groups may also benefit. This is
not automatically the case, because species-specific threats may not apply to
all groups; for example, small birds are unlikely to be affected by the hunting of
large mammals, and timber trees will continue to stand long after medicinal
herbs have been lost. But monitoring the impacts of threats is an important first
step in improving forest management.
6
A similar approach applies when surveys focus on species that are
known to be rare, on the basis that if conditions are suitable for the rarest forest species, then commoner forest species will probably have healthy populations. However, the current and past causes of rarity vary greatly, and therefore limit the usefulness of rare species as indicators. Nonetheless, if a number of nationally or globally rare species are present then the condition of the
forest ecosystem is likely to be good.
To assess the impacts of forest habitat change across a wider range of
species, a set of indicator species are often selected from (a) particular taxonomic group(s) about which there is a good body of taxonomic and ecological
knowledge. For example, changes to a forest habitat have been shown to
influence the population densities of forest-specialist bird species (e.g.
Newmark, 1991), and the factors that have caused their decline may also affect
forest specialists in other taxonomic groups. But we need to research whether
‘sensitive’ species in different taxonomic groups all respond in the same way to
the same changes in the forest ecosystem. Pending such an investigation,
caution is necessary before extrapolating impacts of forest change from one
indicator group to another.
Besides being cautious about the use of indicator species, care is
needed with regard to the seasons and timescale over which surveys are carried out. In some seasons, species may be easier or harder to locate because
of particular behavioural traits: breeding, migration, food abundance and so on.
To get year-round data, surveys need to be carried out in different seasons.
Furthermore, long timescales need to be used if ecosystem functions are to be
monitored, because the impact of species declines on other processes may
take a considerable time before they are felt. For example, some trees whose
seeds are dispersed by elephants may decline over decades as a result of the
elimination of large mammals by hunters.
2.2
Forest management
From the outset, it is important to stress that conservation and sustainable use of forests can only occur if forest habitat is maintained. Forest cover
can include indigenous, naturally regenerating forest, and planted/managed
forests of indigenous or exotic species. Trees planted on farms are also important for biodiversity, especially where they act as corridors connecting different
forest patches. However, having emphasised this basic point, not all types of
forest are equally important for the maintenance of biodiversity.
Most of the natural forests in Africa face pressure from communities who
derive their basic livelihood from forests, or the land on which they grow, and
even greater pressure comes from commercial plantation companies and
7
extractors of timber and other products. Conflicts often occur as a result of
competition for forest resources from local people’s livelihoods, commerce,
wildlife and forestry, and the alarming rate of biodiversity loss in African forests
poses an international concern.
International and national discussions and processes, such as the
national Tropical Forest Action Plans, the UN Forum on Forests and the
International Timber Trade Organization, have all been developed to address
this problem. These processes are mirrored by the conferences of the
Convention on Biological Diversity, and its related Biodiversity Strategies and
Action Plans, which include decisions on forest biodiversity.
While these international policy processes evolve, there is a pressing
need to address the conflicts on the ground, and inform policy debate with
appropriate information on the range of uses that forests can fulfil. Also, it is at
the field level that decisions need to be taken, by the owner/steward of a forest
area, on the management aims for forest areas.
Box 2: Examples of forest management aims
●
●
●
●
●
●
●
Ensure high quality fresh water at acceptable flow-rates, minimise
erosion and movement of soil, and stabilise hillsides, through forest
management in watersheds.
Conserve a representative sample of a biological region
(province, biome or habitat) in a state relatively unaltered by
modern man, and avoid the loss of species and erosion of
genetic diversity.
Maintain areas and features that are essential for ecological
processes, such as migrations and biological cycles, and
rehabilitate degraded areas.
Protect sites of cultural or archaeological importance.
Ensure the supply of wood and non-wood products to satisfy
local/national/international demand.
Provide facilities and opportunities for tourism, recreation,
environmental education, research and monitoring.
Retain a maximum choice of land-use options for the future.
Developing and implementing forest management plans through consultation processes, involving civil society (especially local communities), government and the private sector, allows different forest users’ needs to be taken
into account. The management plan can then include actions to prevent damage to ecological services, and limit loss of genes, species and forest habitats,
while forests continue to supply important goods and services. Drawing up
8
multiple-use management plans to address this range of issues requires a
number of different types of information.
Box 3: Sets of information needed for forest
management planning
●
●
●
●
Physical features: location; area; altitude; topography and drainage;
infrastructure (including villages); climate.
Biological resources: biodiversity; abundance and yields of commercial species.
Social, policy and legal framework: the population density, with an
assessment of the proportion and distribution of indigenous, local and
recently arrived groups; patterns of forest use by different groups; and
national and traditional laws relating to land ownership, forest use and
management, and their effectiveness.
Economic context: what economic policies and market forces
are influencing the rates at which different forest resources
(including forested land) are being used?
It is the responsibility of those carrying out biodiversity surveys to present their results in a form that can be understood by people interested in
managing the forest (not just technicians and scientists), so that social,
economic and biological information can be integrated, and the information
understood by local people, government and private enterprise.
The results also need to show the links between the details of forest
resource availability, and the bigger picture of national or regional patterns of
forest use and national development. Survey questions should be guided by
information from household surveys on patterns of forest use, and market surveys of commercial patterns of use, road-side sales, bushmeat markets, and so
on (see section 2.6). The links between in-forest and out-forest data collection
need to be carefully considered.
2.3
Research into forest biodiversity
Carrying out the forest surveys described in this manual will help identify
research needs, and the results of these surveys should also provide the first
steps in answering many research questions. Although time is one of the
greatest restrictions on surveys, it is important to note that data becomes more
robust as it accumulates over days, weeks, months and years. This manual
focuses on getting started, so that the presence/absence of species can be
assessed, and the relative abundance of some of the commoner and
9
more conspicuous species gauged. For more thorough ecological monitoring,
poor visibility in forests requires that a great deal of time and effort be expended before reliable results can be obtained (e.g. Walsh & White, 1999; Plumptre,
2000; White & Edwards, 2000).
Perhaps one of the most important constraints to gathering useful information for multiple-use management is that inter-disciplinary research teams
are few, and there has been little investment in developing research or survey
methods that integrate biological, social and economic information. This is a
key area of research that needs to build upon the foundations laid by ethnobiological and socio-economic studies, so that the interests of different stakeholders can be included in planning processes. This is especially true for those
indigenous and local communities that already possess a wealth of knowledge
about biodiversity and its management.
There are precedents for carrying out participatory forest surveys, where
local specialists plan and implement surveys, in collaboration with other parties,
to agree on resource abundance, or to monitor patterns of forest use. Indeed,
programmes for training ‘para-taxonomists’ have been developed, in which
local experts are given training which enables them to integrate their knowledge
with scientific and technical information. In this context, it is important that all
fieldwork conforms to international standards on ethical and legal practice in
the field (see below), respecting local knowledge.
Immediate priorities for applied research include developing survey
methods that can be used for rapid, problem-oriented inventories and monitoring. One of the subsidiary aims addressed in this manual is to focus attention
on the need for more biodiversity information to be incorporated into
Environmental Impact Assessment (EIA) checklists for forests in Africa. To
date, little has been done to develop biodiversity criteria or indicators that can
be used to assess or monitor impacts of road-building, agriculture and other
developments on forest biodiversity in adjacent areas.
While answering these pressing management questions, pure research
into forest biodiversity continues to be vital, and many of the summary statements about ecology that are made in the chapters that follow are based on
long-term and meticulous research efforts. Furthermore, the information accumulated at long-term sites, with well-studied populations, is essential for calibrating results from rapid surveys with known population figures. We still need
research to understand what controls plant and animal population densities,
and what elements of plant–animal interactions are central to maintaining
healthy forest ecosystems. In addition, continued research in the field of
taxonomy is necessary to ensure that accurate and consistent species names
are attributed to field records.
10
2.4
Ethical and legal standards
Whether field activities are short or long-term surveys, and whether carried out by national or visiting scientists, international standards of ethical and
legal practice need to be followed (e.g. Fauna & Flora International, 2000).
These have been compiled by a number of institutions, especially those concerned with anthropological work, and the reader should refer to the full texts if
there is any uncertainty about planned actions. In general, care needs to be
taken:
●
to ensure that official research permits, including collecting permits
and equipment import licences, have been provided, and that a
sponsoring national institution has approved and supports the proposed survey work. Also ensure that any products that arise from
the work (including reports, books, scientific papers, films, etc.)
acknowledge the sponsoring institution, and provide copies to them
and other government departments.
●
to endeavour to work with and through local institutions, building
from their capacity and taking their advice. Wherever possible contribute to building local capacity. When employing local field assistants ensure that local labour codes are respected.
●
to collect animal specimens in a humane and ethical manner, with
as few specimens collected as necessary to satisfy scientific needs,
and with the absolute minimum amount of pain or suffering inflicted
upon the animal.
●
to take account of beliefs, customs and rights of local communities,
and guard against the appropriation of their intellectual property.
2.5
Preparations
Successful surveys require careful planning and preparation. In particular, you must think carefully about the purpose and objective of your survey, as
this will determine the information that you need to obtain, and thus the
methodology that is most appropriate. In addition, before you start surveying,
you need to think how the data will be analysed. This is vital in order to
develop an appropriate sample design. Although detailed discussion of data
analysis is beyond the scope of this manual, some simple considerations are
provided to help you ascertain whether the chosen method will prove useful for
statistical analysis.
Tips on identification are provided in each chapter. However, it is well
worthwhile spending some time in museums inspecting skins, perusing field
guides, and taking opportunities to visit field study sites. Through all of these
11
methods, and by speaking to knowledgeable people, it is a good idea to start
compiling a species list for the forest sites, or general regions, that will be
visited.
Besides general reference books, atlas projects can provide very useful
indications as to the possible occurrence of a species in a particular area. For
example, bird atlas projects are underway or completed in a number of countries (for example, the whole of southern Africa, Kenya, Tanzania and Uganda),
and a list of species recorded for a particular atlas square (or point, in the case
of Uganda) can usually be produced on request to the coordinators.
As well as being able to identify particular species, many of the survey
methods described here rely on accurate estimation of distances. It is very
important to practise distance estimation before you start your work. If you are
using a cut-off point of 25m, for example, go into the forest and estimate this
distance, then measure to see how accurate your estimation was. Continue
practising until you can estimate this distance reliably in this habitat. Indeed, it
is important to practise this in a similar vegetation type to the transects; distances appear very different in the open when compared to dense forest, and
stride lengths tend to become much shorter when hopping over logs, running
away from driver ants, or wading through a swamp. It is crucial that all those
who are counting are accurate in their distance estimation.
The latter point, namely the discrepancies that result in distance estimations as a result of people judging distances differently (see Mitani et al., 2000),
argues well for the use of an optical range finder. The reliability and accuracy
of optical range finders has made them an invaluable tool in the field, all the
more so because all transect methods assume distances are exact. It takes little time to learn how to use an optical rangefinder properly, and they generally
are inexpensive given the costs of a survey.
Survey equipment
Although each chapter makes reference to special equipment and/or
personnel necessary to conduct the individual survey methods, there is some
basic equipment that is common to all surveys and may be considered as
essential items to be carried into the field. It goes without saying that suitable
clothing, footwear, field bags and camping equipment are basic necessities.
●
notebook (with plastic bag for rain protection): many people prefer
to use a loose-leaf binder, so that only the notes for a particular
field session are taken to the field. Previous notes can then be kept
elsewhere for safety, and photocopied as soon as one returns from
the field session. The importance of keeping duplicate records
(either by using carbon paper in the field, or by photocopying), or of
backing up information electronically, cannot be over-emphasised.
12
●
●
●
●
●
●
●
●
The advent of hand-held computers or personal data assistants
(PDA’s) appears set to revolutionise data input/collection.
data recording sheets or forms: these can be designed and
photo-copied in advance, or simple formats can be reproduced
daily in a notebook or binder.
topographic maps of the survey area, on as large a scale as
available, and map of trails, footpaths, etc. if available (you may
have produced your own map from reconnaissance surveys).
prismatic compass (in a protective case): essential, not only for
making maps and determining survey routes, but also to help
teams return to camp if they get lost.
pencil/pen: propelling pencils, which need no sharpening, are most
convenient, or pens with waterproof (India) ink. Ordinary ballpoint
pens are NOT recommended for data recording: the ink is not
waterproof, and your data sheet or notebook will be a mess if it
gets wet.
torches (preferably six-battery) and headlamp for night-time work
(spare bulbs and batteries are essential).
watch and/or stopwatch (should be easy to read in dim light
conditions).
field identification guides: these are discussed in more detail
under the ‘Methods’ section of each chapter. Avoid the use of large,
cumbersome reference works (which are best consulted back in
the office/laboratory), and stick with lightweight, compact field
guides. A species checklist for the area (if available) is advisable,
or a preliminary list compiled from expected occurrences.
binoculars: these are the most essential piece of equipment for
surveys of larger mammals, and especially birds. Binoculars are
normally labelled as 7x30 or 8x40, and so on. The first figure represents the order of magnification, and the second the diameter of
the objective lens measured in millimetres. The larger the second
figure is, the greater the light-gathering potential of the lens. For
forest work, a wide field-of-view and plenty of light-gathering capacity is best. The best magnifications are 7x and 8x; higher magnifications (10x) may allow you to identify birds in the treetops more easily, but will be less effective for more close-up work. The objective
lens should be at least x40. A telescope (mounted on a light-weight
tripod) is surprisingly useful for identifying treetop birds. Ideally,
both binoculars and telescopes should be weather-proof; if they are
not, then carry strong plastic bags for protection against rain (ziplock bags are useful if available).
13
●
●
●
●
photographic equipment: a good camera is often useful for taking
photographs of survey areas, different types of habitats, evidence
of human activities, captured or surveyed specimens, etc.
Equipment can range from inexpensive instamatic cameras that
provide basic records of survey areas or details of animals and
their signs, to expensive telephoto equipment for quality images
that can be used in campaigns to raise awareness and as
education materials. Different film speeds, an assortment of lenses,
a flash (for photography in poor light conditions), and a protective
bag are recommended. In addition, the increasing availability,
resolution and affordability of digital cameras means that they are
now a very valuable tool for specimen identification and for
permanent recording of habitats trapped in, and so on. A quick
digital image of each trap line (or specimen) is a cost-effective, or
at least a valuable, addition to written descriptions of habitat (or
specimens).
optical (or laser) range finder (for estimating distances).
(optional): Global Positioning System (GPS) for recording the
start and end of transects, or positions of point counts.
a first-aid kit (see below).
There is, as they say, no substitute for experience, and if you have not
conducted many surveys it is important to try to have in your team experienced
surveyors to help you.
2.6
A note on market surveys
and questionnaires/interviews
Although not discussed for each group, there are two additional survey
methods which have great relevance for surveying African forest vertebrates:
market surveys and questionnaires/interviews.
Local markets can produce some interesting information about the local
fauna, especially for general surveys. This is especially so for vertebrates in
West and Central Africa, particularly in light of the boom in the bushmeat trade.
In many markets there are stalls selling dead mammal species such as small
antelope (particularly duikers), monkeys, chimpanzees and gorillas, pangolins
and rodents, especially canerats (or grasscutters, as they are known in West
Africa). However, determining the origin of market carcasses is often very difficult, especially for smoked meat that has been trucked a long distance and
been through the hands of a number of intermediaries.
14
At the local level, even more important are interviews with local people
ranging from local farmers, and particularly those that hunt, to forest, wildlife,
national parks and other government officers. These people have considerable
knowledge about animals in the area where they live and work, but care must
be taken in verifying their verbal reports. For example, many villagers fail to
recognise animals from pictures in guidebooks, and misunderstandings can
arise through the misuse of local names, etc. Hunters, who tend to be most
knowledgeable, are often reticent on the whereabouts of their future bag. Only
clear descriptions and explanations, ideally from independent sources, should
be recorded, and these should only be added to the dataset after further verification.
Having noted the limitations of market surveys and interviews, which can
only be overcome through several months of field work, much information on
forest animals’ ecology, population status and levels of threat can be obtained.
This has been done effectively for forest animals in: Sierra Leone (Davies &
Richards, 1991); south-east Nigeria (Angelici et al., 1999); Democratic
Republic of Congo (Dupain et al., 2000).
2.7
Health and safety
Survey work involves many health and safety risks, including injury,
infection, and disease.
Safety precautions during observational surveys are largely common
sense, and include wearing the correct clothing and using the right equipment,
and, if possible, working in pairs rather than alone. When doing any kind of
work off well-used trails, ensure that you have a GPS or compass, and a map,
and that other members of the team know where you are working. Good survey
management dictates that a basic first-aid kit is carried along on field work at
all times, that everyone knows where the first aid equipment is, and that everyone knows how to use it. Discuss possible problems with medical experts
before starting the expedition so that the first aid kit is correctly and
appropriately equipped.
Working with large mammal species, like primates, ungulates and carnivores, carries with it obvious risks. Be constantly on the alert and aware of your
surroundings, being careful not to become so focused on a particular bird or
reptile that you lose awareness of other, more dangerous wildlife.
Handling small mammals, herptiles and birds also carries the risk of
infection from disease or ectoparasites. Protective gloves and a surgical/facemask may be necessary depending on the type of work being done. Always
wash your hands thoroughly after handling any animals.
15
A wise precaution before undertaking any survey work is to get injections
against tetanus and rabies. This may require more than one injection, so allow
time for the full course before the fieldwork begins. Similarly, courses of antimalarial tablets often need to be started several days before departure (and
should be continued for several weeks after leaving the malaria area).
Additional notes on health and safety, where relevant, are provided in the
individual chapters.
2.8
References
Angelici, F.M., Grimod, I. & Politano, E. (1999). Mammals of the Eastern Niger Delta (Rivers and
Bayelsa States, Nigeria): An environment affected by a gas-pipeline. Folia zool. 48(4): 249–264.
Davies, G. and Richards, P. (1991). The Rainforest in Mende Life. Unpubl report. Escor/ODA,
London.
Dupain, J., van Krunkelsven, E., van Elsacker, L. & Verheyen, R.F. (2000). Current status of the
bonobo (Pan paniscus) in the proposed Lomako Reserve (Democratic Republic of Congo). Biol.
Cons. 94(3): 265–272.
Fauna & Flora International. (2000). Code of conduct for researchers. Oryx 35 (2): 99.
Mitani, J.C., Struhsaker, T.T. & Lwanga, J.S. (2000). Primate community dynamics in old growth
forest over 23.5 years at Ngogo, Kibale national park, Uganda: implications for conservation and
census methods. Int. J. Primatol. 21: 269–286.
Newmark, W.D. (1991). Tropical forest fragmentation and the local extinction of understorey birds
in the East Usambara Mountains, Tanzania. Conserv. Biol. 5: 67–78.
Noss, R.R. (1990). Indicators for monitoring biodiversity: a hierarchical approach. Conserv. Biol. 4:
355–364.
Plumptre, A.J. (2000). Monitoring mammal populations with line transect techniques in African
forests. J. Appl. Ecol. 37: 356–368.
Walsh, P.D. & White, L.J.T. (1999). What it will take to monitor forest elephant populations.
Conserv. Biol. 13: 1194–1202.
White, L. & Edwards, A. (2000). Conservation Research in the African Rain Forests: a Technical
Handbook. Wildlife Conservation Society, New York, USA.
16
3.
Amphibians and reptiles:
the herptiles
Kim Howell
twig snake (Thelotornis kirtlandii)
3.1
Biology
Herpetology is the study of amphibians and reptiles, and these two
groups will be collectively referred to as herptiles in this chapter.
Amphibians (Class Amphibia)
The best known amphibians are the anurans, the frogs and toads, of
which there are about 161 species in East Africa, supplemented by about 10
species of apodans or caecilians (legless forms) found in forests in Kenya and
Tanzania; there are about 600 anurans and 22 species of caecilians known
from the continent. Apodans live mostly in moist soil, and emerge only after
heavy rains, and, although the same can be said for many anurans, our discussion of survey methods focuses on frogs and toads, excluding the few species
which are entirely aquatic. Furthermore, the assessment of larval forms is only
briefly addressed; this topic is covered in more detail by Heyer et al. (1994) in
their detailed review of amphibian survey methods.
Most frogs and toads are extremely seasonal in their reproductive
behaviour. In drier periods, many seem to simply disappear; they seek shelter
where they will not be exposed to desiccating conditions, and are not seen or
heard during the daytime or at night. However, during the rainy season(s)
amphibians emerge and become much more active. They may still remain relatively hidden during the daytime, but at night male frogs and toads of many
species produce loud vocalisations that serve to advertise their presence in
order to attract females and also to defend their territories from other males.
17
Reptiles (Class Reptilia)
It is mostly the snakes and lizards that occur in forests, though terrapins
may be associated with wetlands in forests, and tortoises are occasionally
found at the forest edge. These come from the following groups of reptiles:
lizards (including geckoes and chameleons); snakes; amphisbaenians (or
worm-lizards); chelonians (marine turtles, freshwater terrapins, and terrestrial
tortoises); and crocodiles. In sub-Saharan Africa, the approximate numbers of
species for these groups are as follows: chelonians (excluding sea turtles), 26;
lizards, 680; amphisbaenians, 66; snakes, 466, and three species of
crocodiles.
Much of our knowledge of reptile distribution in forests is still rather limited, being restricted to preliminary species lists. For example, in Tanzania at
least four species of lizard and two snakes new to science have been found
within the past few years (Broadley, 1994, 1995a,b; Broadley & Wallach, 1996;
Pasteur, 1995) and more surveys are needed. Reptiles are found from below
the soil level to the tree canopy, so there are a variety of forms ranging from
the fossorial to the arboreal.
3.2
Management issues
Worldwide, amphibians seem to be declining for poorly understood reasons (Wyman, 1990). Recent research indicates that two cases of frog mass
extinctions in rain forests are a consequence of fungal pathogen attacks
(Berger et al., 1998), and elsewhere tadpole deaths from fungal attack have
been linked with climate change and ultra-violet radiation (Kiesecker et al.,
2001). We do not have data on the impacts of pesticides, but given the
increasing use of agrochemicals, and the general increase in aquatic pollution,
there is a need to monitor the levels of pollutants in the environment as well as
in the tissues of amphibians.
As in other groups of vertebrates, there seems to be a basic split
between non-forest and forest species, and there is also a distinctly forestdependent element that does not occur outside closed forest (e.g. Howell,
1993). The forest-dependent amphibians are vulnerable to forest alteration
and/or clearance, and are under threat in many parts of Africa. We do not yet
understand the physiological reasons for the dependence on forest, but the
number of hiding or retreat sites is a possible critical factor in limiting tropical
forest anuran populations (Stewart & Pough, 1983; Howell, 1993), especially if
forest quality is altered, and/or forest patch size decreases.
It is worth noting that this chapter focuses largely on amphibians which
are forest dwellers, and which make use of temporary pools for breeding, or
which are independent of free water for reproduction (e.g. Nectophrynoides
18
spp. toads, Arthroleptis spp. frogs, the bush squeakers, and some microhylid
frogs). However, recent studies have shown that even savannah species that
breed in seasonal wetlands rely on forest as a dry season refuge.
Aside from local extinctions of forest-dependent amphibians and reptiles
as a result of forest loss and degradation, the isolation of once continuous populations can be another problem. At present, no data exist as to the long-term
effect of such isolations. A corollary to this is that areas of degraded forest may
effectively become a means by which non-forest dependent species can
invade; this already has occurred in many places along forest roads. In Africa,
the paucity of information makes it difficult to develop predictive models for the
abundance of amphibians and reptiles based upon capture data and measures
of habitat quality.
As many species of forest-dependent reptiles (and a few amphibians)
are sought after by collectors for the live animal trade, there is a particular
need to be aware of this pressure, especially on populations in already isolated
forests, or near sites frequented by visitors. Commercial collecting, for example
of chameleons, should be discouraged in such places. The larger reptiles
would appear to be relatively long-lived, and intensive commercial collecting in
a small area may have significant effects on populations.
Amphibians and reptiles form an important part of the forest ecosystem,
where they are significant predators on invertebrates as well as smaller vertebrates, and they themselves are important food items for birds and mammals.
This also applies to large snakes (whether venomous or not), which eat many
rodents, and can therefore also be beneficial to villagers.
A management issue peculiar to snakes is that because some of the
larger, more conspicuous species are venomous and potentially dangerous to
man (see section 3.5), snakes in general are often regarded as harmful, and
killed. In fact, relatively few species of snakes are dangerous to man, and it is
important for managers to be aware of this, and also to educate others that it is
not necessary to kill all snakes. This will undoubtedly encounter cultural resistance where snakes, and other herptiles, are part of local peoples’ belief
systems.
3.3
Methods
General
Our lack of knowledge about most forest herptiles means that current
surveys deal largely with the building up of species lists, rather than indices of
abundance or population studies (e.g. Broadley & Howell, 1991; Drewes &
Vindum, 1994). Efforts have been made, in West Africa (Barbault, 1975) and in
19
eastern Africa (e.g. Western, 1974; Kreulen, 1979), to estimate populations of
reptiles, but these have usually been of large and/or conspicuous species in
open, drier habitats.
There are, therefore, few standard methods that have been used to
quantify amphibian and reptile populations. Those that have been used in
Africa have dealt with forest, leaf-litter-dwelling anurans and reptiles in
Cameroon (Scott, 1982), or anurans in open areas such as small seasonal
breeding ponds (Bowker & Bowker, 1979). No satisfactory methods have yet
been developed to sample the arboreal tree frogs, the fossorial apodans, or
canopy-dwelling reptiles that are the focus of this chapter. Chameleons, for
example, are hard to detect during the daytime and are best surveyed at night
(e.g. Broadley & Blake, 1979; Jenkins et al., 1999), while snakes are very
mobile and also difficult to detect. Studies of populations of anuran larval populations also appear to be lacking in East Africa.
Identification
A number of useful references and field guides are available for identifying amphibians. Frost (1985) edited a world list of amphibian species that
serves as a basis for national and regional lists; in addition, African tree frogs
are covered by Schiotz (1999). Other African national lists include: Stewart
(1967), which provides a general introduction to some of the species found in
eastern Africa; Rodel (2000), which covers many savannah species in West
Africa; Fischer and Hinkel (1992), which describes Rwandan forms; Passmore
& Carruthers (1995), covering South African frogs, many found in open habitats; Pitman (1974) which covers the snakes of Uganda, and Lambiris (1989),
which gives useful general information on the biology of many species in
Zimbabwe, including drawings of the tadpoles. At least two of the newer guidebooks feature CD-ROM recordings of frog vocalisations (Passmore &
Carruthers, 1995; Rodel, 2000), which allow species identification without the
need for specimen collection.
Field guides currently available for reptiles are Branch (1998), which covers southern Africa and includes many common woodland (but not forest)
species found in eastern Africa; MacKay & MacKay (1985), which gives details
on how to identify venomous snakes in East Africa; and Broadley & Howell
(1991), which provides a key and annotated list of species for Tanzania.
Spawls et al. (2002) will provide coverage for East Africa, including Rwanda
and Burundi. Older references include: Spawls (1978), which lists snakes of
Kenya, and Schmidt & Noble’s (1919–1923) recently reprinted descriptions for
West Africa. Glaw & Vences (1994) should prove useful to anyone conducting
surveys of Madagascan herptiles.
20
3.3.1
General surveys
When visiting an area for the first time, either to begin building up a
species list, or to carry out a rapid assessment of sites for future studies, a
general survey can be carried out to gather basic information.
General surveys provide at least a minimum of information on species
which may be present in an area. It is usually after a general survey has been
conducted and unusual and/or interesting species found that more detailed
studies are conducted. In most cases, a general survey will be done over a
short period of time using qualitative rather than quantitative methods of sampling and with little or no strict sample design. Nevertheless, general surveys
are a useful way to involve local residents in participating in activities and winning their good will and confidence; they often have a detailed local knowledge
of particular species or habitats, and without their assistance a survey will usually fail to detect even common species which may be present.
Equipment
●
●
●
●
●
●
●
●
cloth bags (various sizes – 80mm x 500mm to 140mm x 1000mm)
plastic bags for specimen collection
short handled rake or hoe for turning stones, logs, etc.
gardening gloves
snake tongs or grabbing stick (for picking up and handling snakes)
a shorter type of grabbing instrument (like artery forceps) for
grabbing small snakes, or controlling the heads of larger ones that
have been grabbed or pinned down with a larger stick
lizard noose (a loop of string held on a stick which permits you to
slip it over the head of a lizard)
catapult for collecting specimens from the canopy
weighing scales
Site selection and procedure
i) It is necessary to take a number of different approaches during a general survey in order to establish whether amphibians and/or reptiles are present. During the daytime, surveying under relatively dry conditions, you should
search hiding places, such as inside rotten logs, under bark, in leaf-litter at the
base of trees (especially between tree buttresses), and in any tree cracks or
holes. Old pit sawing sites in the forest, with the associated moist sawdust and
rotting stumps and planks, have also proved especially productive. For microhylid anurans, crevices in road cuts and banks of soil should also be searched.
ii) More and more emphasis has recently been placed on the need to
sample not only adult amphibians, but also the larvae (e.g. frog and toad
tadpoles). For many African species, these have not yet been described, and in
21
many cases the adults may no longer be in the area, leaving only the tadpoles
as evidence of the species’ presence. There is thus a need to sample tadpoles,
catching them with simple nets (mosquito netting sewn onto a small wooden or
metal frame is fine for non-quantitative methods), seeking them in aquatic vegetation and under rocks and logs in pools where they like to hide. The eggs of
amphibians can also be diagnostic of a species, and these should be collected.
iii) It is useful to raise the tadpoles, from eggs if possible, in order to
monitor their features as they develop, and eventually identify the species once
the larvae have metamorphosed into adults. This involves keeping tadpoles in
jars; many are filter-feeders and will survive on the water from the collecting
site, as long as it is regularly changed. Each larval developmental stage should
be collected and stored in 10% formalin solution, with careful labelling. An alternative is to collect from the site over a period of time that allows all stages of
development, from egg to adult, to be collected. However, either method is time
consuming, and may not be feasible during short survey visits. A more detailed
and quantitative approach to estimating tadpole densities is given by Heyer et
al. (1994).
iv) Night-time surveys for amphibians, and perhaps some geckoes,
involve listening for (and making tape recordings of) vocalisations, and visual
searching of suitable resting sites with headlamps and torches. Streams that
flow through forests can be sampled using both pit-fall traps, as well as audio
transects (as long as the background noise of rushing water does not block out
the frog vocalisations). Remember that while some frogs and geckoes live on
the forest floor, others are found at varying heights, at least up to 5m, on trees.
v) Reptiles can often be collected in similar situations to amphibians,
namely under rocks, the bark of trees, and so on. They may also be seen
basking on and above the ground. Indeed, it can be helpful to place sheets of
metal, wood and cardboard besides tracks and roads to attract reptiles. Nighttime collecting is also required for some snakes, geckoes (none of the east
African species give loud vocalisations), and chameleons; the latter are often
visible when asleep, clinging to vegetation at different levels above the ground.
Be especially aware of the need to collect fossorial and burrowing forms, such
as blind snakes and legless lizards – these are seldom sampled and poorly
known. It is important to realise that general surveys are likely to under-represent the larger species, such as ridged or grass frogs (Ptychadena), and some
tree frogs.
vi) Indirect methods may be employed to detect the presence of a
species, such as through information from local inhabitants (indigenous/local
knowledge) and by examining the faeces/scats from some predators. The
identification of reptile bones in owl pellets, and prey remains of large raptors,
especially crowned eagles (see Msuya, 1993), as well as reptile and amphibian
22
remains in mammal faeces, may all provide information on the presence of a
species (see Yalden, 1977). This is important in the case of apodans and legless lizards that are often not detected by conventional trapping but may be
prey items of larger snakes.
vii) Information gathered during these general surveys could be used to
stratify a large area into separate zones with characteristic differences (e.g.
marshy; woodland; near rivers) that influence herptile distribution and abundance. Thereafter, longer surveys and studies may be carried out in each of
the various zones so that a full picture of the herptiles in a forest region is
obtained.
Recording
i) Record each individual animal and its species name (Form 3.2). If you
do not know its name, then call it ‘species a’, etc.
ii) Take the standard measurements for each specimen along with any
geographical and habitat information. General data required is similar to that
collected for small mammals (section 4.4), with some obvious differences. In
particular, some additional notes and measurements should be recorded
including snout length (in the case of reptiles), iris colour/shape, and any other
notes on anatomy, such as eyes (e.g. protruding) and feet.
iii) Detailed notes need to be made of the colouration of the animal, supported, if possible, by colour or digital photographs (some people prefer to take
these after the animal has been anaesthetised). Colour is a key feature in the
identifications of amphibians, and once immersed in preservative the bright
colours often fade to brown or white.
iv) Collect and preserve voucher specimens (see section 3.4)
Advantages/limitations
The general survey technique continues to yield important information in
East Africa, but is best used in conjunction with some of the following techniques such as pitfall traps and litter searching. Unfortunately, it does not provide information concerning populations, and it is difficult to quantify the results
obtained from this type of collecting survey, especially given seasonal and
annual variation.
3.3.2
Drift fences and pitfall traps
This is a method that has been employed recently for sampling small
mammals in forests, and has been shown to be especially effective in sampling
leaf-litter frogs of the genus Arthroleptis, as well as Bufo toads and forest floor
lizards.
23
The basic principle behind this trapping method is that animals on the
forest floor encounter a barrier termed a ‘drift fence’ which causes them to drift
into the trap. Rather than cross the fence, burrow under it, or break through it,
they take the route of least resistance by moving either right or left and following the fence – which leads them to drop into a pitfall trap.
A variety of patterns of arrangement for the bucket pitfall traps have
been used, with varying degrees of success (see Bury & Corn, 1987).
Presented here is the simplest arrangement: a drift fence in a straight line,
termed here a ‘pitfall line’ (Fig. 3.1), using 20-litre plastic buckets for the pitfall
traps and plastic sheeting for the drift fence.
Fig 3.1: Drift fence and pitfall trap
5m
pitfall
bucket
wooden
stake
plastic
sheeting
Equipment
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eleven plastic buckets (size: 20 litre), or any reasonable alternative
which is sufficiently wide to prevent animals jumping across, and
sufficiently deep to prevent them jumping out (for example, large
empty tins). It is important to use containers that are readily available. The buckets should have covers so that they can be closed in
rainy weather or when they cannot be monitored.
plastic sheeting (length: 55m). This may be transparent or coloured;
if the latter, black is likely to be a better choice, since bright colours
may influence the catchability of some species. The exact height
and thickness are not critical and may be determined by availability;
plastic sheeting is often sold as a roll of open-ended tubing in
approx. 0.5m widths, so this can be cut and used as a single thickness. Locally available alternative material may be equally effective
(e.g. polypropylene gunny sack material, etc.).
wooden stakes to support the plastic sheeting.
staple gun and staples for attaching sheeting to supporting stakes
(alternatively, you can punch holes in the sheeting and tie it to the
stakes, but this requires much more time).
24
●
●
a hoe and pick suited to cutting through roots.
measuring tape or string of measured length.
Site selection
Moist or low ground is usually a good place to trap, especially at the
bases of valleys, but try to set pitfall lines in a variety of situations and habitats
for comparison. Remember that altitude is an important variable in the distribution of amphibians. For comparisons to be made, the same method should be
used at each sample site.
Procedure
i) Configuration of trap lines: each trap line is 55m long, with buckets
placed every 5m. Thus, with one bucket at the beginning and one at the end,
the total number of buckets is 11. There is nothing sacred about using a line
55m long, and you can always use a shorter line depending on local circumstances, but it is best to try to standardise the length and set-up so that you
can compare catch rates between different sites.
ii) Each bucket is sunk in the ground so that the upper rim is equal to, or
slightly below the ground-surface level. This is very important; apparently, few
animals will climb a mound of soil at the edge of a bucket, whereas if the
bucket is level with or slightly below the soil surface, they readily fall in.
iii) The plastic drift fence is erected so that the line is continuous from
the first to the last bucket in each line. The fence should pass over the centre
of each bucket. The best way to keep the plastic erect is to drive stakes into
the ground along the drift fence and then to staple the plastic sheeting to the
stakes. A stake is needed on either side of each bucket, and then at least four
to support the area of plastic sheeting between consecutive buckets. The line
does not have to be straight, and probably will have to curve in places in order
to avoid trees, large rocks, and other obstacles.
iv) It is important to clear away vegetation that gets in the way of the
plastic drift fence. The plastic sheeting must rest flush with the ground; if vegetation props the bottom open, animals will move underneath the fence. Once
the fence is in place and properly stapled, it is time to mound up a little soil on
both sides of the fence (to further inhibit animals from pushing underneath).
v) It is good practice to number each separate pitfall line, and then, within each line, number each bucket. This is best done with flagging tape attached
to a nearby stick. Try to map the pitfall line exactly using a GPS (Global
Positioning System) or use longitude and latitude coordinates to allow surveyors to come back to the exact spot and repeat the sampling. You also may
wish to establish permanent markers indicating the sites of your pitfall line.
25
vi) Remove litter such as leaves and soil from buckets daily. Check
buckets regularly for stones or branches that may have fallen in as these may
allow animals to climb out. To ensure rain water drains from buckets, puncture
the bottom of each, and the sides if necessary (this also reduces the attractiveness of the buckets to local residents!).
vii) Important note: When checking pitfall lines in early morning and late
afternoon or at dusk, or any other stage when the light is deteriorating and visibility is poor, always use a torch when examining the contents of the pitfall
buckets. Scorpions, centipedes and venomous snakes may be in the bucket in
addition to the frog you are about to pick up. Look carefully before you put
your hand in the bucket!
viii) After you have finished your trapping regime and removed the pitfalls and drift fence, fill in the holes that were dug for the buckets. This ensures
that no animals will accidentally be trapped and no larger animals will injure
themselves when walking in the area. This will also enable the site to recover
quickly, an important point if you wish to sample the same area at another time.
Recording
i) Detailed notes should be kept on local habitat, soil type, amount of leaf
litter, ground cover, etc. for each pitfall line (Form 3.2); those describing the
exact surroundings of each bucket may also be taken.
ii) The number of animals captured per night in each bucket should be
carefully recorded; these data can then be combined to calculate the trap success of each pitfall line. It is important to record from which bucket each animal
came, rather than recording just catch per line. This permits later analysis,
which may indicate which features of the microhabitat are related to the
capture of particular species.
iii) Information on captured species should be recorded on the standard
form (Form 3.1).
Data analysis
i) Most general survey work involving pitfalls will simply record trap success, i.e. how many captures per number of (bucket) trap nights. This may then
be compared with similar trap success for other types of traps, such as breakback traps in the cases of small mammals.
ii) Trapping success of pitfall lines at different elevations, or in different
habitats, may also be compared.
iii) If adequate data are kept over a long period of time, it may also be
possible to study microhabitat features by comparing trap success of buckets,
for example, which are located near fallen logs and those which are not.
iv) Simple graphs can be plotted of cumulative number of species (CNS)
and cumulative number of individuals (CNI) against cumulative number of trap
nights. If the CNS curve flattens out by the end of the sampling period, with few
or no species added during the last nights of trapping, then sampling likely has
detected most of the species which are detectable using that method.
26
Advantages/limitations
i) The advantages of this technique are that it is easily repeatable, can
easily be modified to suit local conditions, and can be used to sample mammals, amphibians and reptiles simultaneously. It is also one of the few techniques that can be used to sample apodans and burrowing reptiles that
occasionally emerge on the forest floor.
ii) It can be used as a non-destructive technique, and permits the markrecapture method of population assessment (see below). However, this technique only samples members of the forest floor community, and so will not
sample tree frogs, for example.
iii) Occasionally, animals such as bushpigs or small antelopes may wander through the drift fence, necessitating repairs. It is good policy to check your
pitfalls first thing in the morning, and then again in late afternoon. A quick check
an hour or two after sunset will also allow you to detect early arrivals, and
these can be removed so that they do not spend the night exposed in the
bucket; in dry, cold forest, some amphibians may perish overnight from dehydration and/or exposure, thereby necessitating more frequent checks.
Fig 3.2: Drift net fence
3.3.3
Canopy walkway trap
A method of setting traps on walkways in the canopy. It involves
constructing a runway of mosquito mesh into which is sewed a funnel-shaped
bag – the funnel trap. The entire construction is then raised by means of rope
and pulleys into the canopy (see Vogt, 1987 for details and a photograph). This
method works on the principle that reptiles will make use of walkways to travel
through the forest canopies.
27
Equipment
●
●
●
●
●
●
●
plastic mosquito gauze (also called mosquito mesh or window
screen)
galvanised wire
metal cutting scissors or tin snips
pliers and wire-cutters
steel rods (diam: 5mm; length: 1m), two for each walkway
pulleys (x 4); several walkways can be tied at different heights to the
same rope and pulley assembly)
nylon or other non-rotting rope to fit pulleys
Site selection
This technique requires a site where the walkway will be touching as
many trees and branches as possible, but will still permit the use of pulleys to
raise and lower it.
Procedure
i) The basic feature of this method is a walkway made of plastic mosquito
mesh (window screen) (Fig. 3.3). Simply use this material in its standard width
(approx. 1m), and in 15-m lengths (or any other length you can conveniently
handle in the field). Metal wire (galvanised if possible to prevent rusting) is
threaded along the entire length of the plastic window screen on both edges; a
length of the same wire is also inserted crosswise at 1-m intervals. These
cross-wires serve to give support to the walkway. A 1-m length of steel-rod
(diam. 5mm) is tied at each end of the screening to ensure a flat entrance onto
the walkway.
ii) Two funnel traps (1m x 0.8m) are then constructed of 8mm x 8mm
galvanised wire mesh and are sewn onto the walkway using galvanised wire at
5-m intervals. The mouths of the funnel traps are as wide as the walkway, so
that any animal that moves along it is directed into the trap. A guide line of
string or rope is attached to both sides of each funnel trap; when the walkway
is raised to its desired height these can be pulled tight and tied to trees or
rocks to prevent it from inverting during winds and rains.
iii) Ideally, walkways should be used at three different levels on the same
set of ropes and pulleys: 3m, 10m, and 15m. The pulley system allows regular
checking of the traps. This is accomplished by lowering both ends of the walkway at the same time.
iv) The funnel traps should be checked regularly, ideally early morning,
midday, and late afternoon. Depending on the trap success and the size of
animals captured, it may be necessary to increase the depth of the funnel
traps, especially if large snakes are encountered.
28
Recording
Information on captured species should be recorded on the standard
form (Form 3.1).
Advantages/limitations
Aside from climbing into trees and capturing by hand, this would appear
to be the only effective method for sampling species which live in the canopy,
or even just above ground level in the forest. However, it is labour-intensive
and requires much experience to perfect. Furthermore, care should be used
when setting and dismantling the trap; always have at least one and preferably
two other people present in case of falls and related injuries.
Fig 3.3: Forest canopy walkway trap
3.3.4
Snake trapping
Fritts (1988) developed a simple trap for snakes made of mosquito mesh
wire. The trap is baited with bird droppings or feathers, and might be effective
for arboreal species that feed on birds. Some snakes detect prey mainly by
olfaction, whereas others respond to visual stimuli. For this reason, it would be
necessary to experiment with different baits. This technique is aimed at assessing populations of a particular species rather than for general survey work (Fig.
3.4). However, it has proved useful even without bait and it can be used as a
simple funnel trap for both lizards and snakes, and seems to work best when
placed along a natural barrier, such as a log, large rock, and other obstacles. It
might also be possible to use it with a drift fence, in an area with hard or rocky
ground which would be unsuitable for pitfall traps.
29
Fig 3.4: Construction of a snake trap
B
A
C
Steps in construction of a snake trap
A)
B)
C)
make funnel from screening and cut 2.5cm – 5cm opening in apex
make cylinder by rolling over the screening and stapling ends;
insert funnel into cylinder and attach two cylinders together with plastic
screening
Site selection
Unless one is setting the traps in a particular grid or other arrangement,
traps should be set in spots which look likely to have sufficient cover to attract
the snake species which are to be trapped. For example, a trap set out in a
completely or relatively open area would probably be less successful than one
set along a natural barrier or hiding site, such as a fallen tree, a rock or a dead
log. Small mammal tracks and paths may also be used by snakes when hunting prey, and these might also make good setting sites.
Procedure and Recording
Information on captured species should be recorded on the standard
form (Form 3.1).
Advantages/limitations
This technique is labour-intensive and extremely time consuming.
30
3.3.5
Capture, mark, recapture
When animals are captured (using one of the methods described above),
marked, and released, the population can be sampled again using the same
methods of original capture to estimate population size. The details of this
method are discussed in Heyer et al. (1994), and summarised in the next chapter (section 4.3.5).
Individual marking of amphibians and reptiles has been done traditionally
by digital clipping: the number and position of digits clipped provides each animal with a unique number with which it can be identified if recaptured. It is
important to be especially careful in the use of methods involving mutilation,
and these should not damage the animal such that it is rendered incapacitated.
Other workers have used tags and even simply tied thread or elastic
bands around the waist of an amphibian to mark it (Muze, 1976), while for
snakes, particular ventral scales may be notched or clipped (Ferner, 1979). The
particular method of marking and numbering is carefully recorded in a notebook, and the animal released (Ferner, 1979; Waichman, 1992).
Marking animals raises ethical issues, especially because much pain
and suffering may be inflicted upon individuals if great care is not taken, and if
appropriate methods are not used. Marking methods should therefore be discussed with experienced surveyors before carrying out fieldwork.
3.3.6
Forest litter plots
In this method, a measured area of 2m x 2m (or any convenient size) is
cleared of every bit of leaf-litter and the amphibians within the area identified
and counted. A portable ‘fence’ of plastic or metal may be used to enclose the
area for ease in sampling. Scott (1982) used this method to sample leaf-litter
anurans in Cameroon.
Equipment
●
●
●
●
●
●
portable plastic or metal fence to help enclose the area to be
searched (made of corrugated sheeting or other material such as
plastic sheeting used in drift fences (see above), c. 15cm high by
1m long, or varying lengths)
short-handled rake and/or hoe
cloth/plastic bags in which to hold sampled animals
spring balances (50g, 100g, 500g, etc.)
tape measure (30m)
preservation material for voucher specimens
31
Site selection
Select sites to be sampled; these will depend on your reasons for sampling. For a general survey, try several different habitat types within the forest,
such as dry, hilly; moist, valley; disturbed versus undisturbed, and so on. It is
important to adequately describe, using standard methods, the habitat and
microhabitat of the area searched. If you are attempting to compare different
sites or habitats, or to assess altitudinal differences or differences between
disturbed and undisturbed areas, then you may wish to randomise your sample
areas within a particular habitat type.
Procedure
i) Measure out the area to be searched and enclose with a suitable
‘fence’. Carefully search through the leaf-litter, using a small hoe or short-handled rake to move the leaf-litter away from a patch of ground in case snakes,
scorpions, etc. are also present. Collect animals by hand and place in cloth
bags.
ii) It is best to sample as many sites as possible; it is likely at least 20
sites with animals present will be needed to meet the requirements of statistical
tests.
Recording
Information on captured species should be recorded on the standard
form (Form 3.1).
Data analysis
This method permits calculation of precise density figures. By measuring
mass it is also possible to calculate biomass per unit area. Depending on how
the sampling was done, it may be possible to compare counts made in different
habitats, at different altitudes, etc. Measures of standard error must then be
calculated to assess the reliability of population estimates.
Advantages/limitations
The method samples only small forest leaf-litter anurans; it is labourintensive and will usually require more than one searcher. In some forests,
herptile densities may be so low as to make assessment by this technique difficult. Microhabitat requirements and/or seasonality factors may result in situations arising in which an area sampled may yield no herptiles, while a plot
immediately near that one might have high numbers. Thus, it is generally
unsuitable for a species with extremely narrow microhabitat requirements.
32
3.3.7
Time-constrained searches
In a time-constrained search, the observer attempts to exert a continuous sampling effort over a particular area or transect for a limited period of
time. For most reptiles and amphibians, this method is difficult to use because
some are extremely cryptic when not calling, and many hide under vegetation.
Nevertheless, this technique may prove useful when animals are conspicuous,
such as at breeding aggregations.
Equipment
●
●
●
stopwatch (or watch which indicates seconds)
plastic/cloth bags
collecting and preserving material
Site selection
Unless you are using a randomised approach, then in practice the
observer picks what would be regarded as a ‘typical’ situation, site or habitat. If
you are sampling an entire study site, then there is a need to identify all of the
major habitat types present. These need to be characterised using standard
methods of habitat and vegetation description.
Procedure
i) Determine an area that is going to be surveyed, and then set a block
of time (5–25 minutes), during which full concentration can be maintained for
searching (in a standardised way). Take rests between search blocks (5 minutes or so). The observer should move slowly along survey transects and other
paths, making every effort to look all around, up and down.
ii) Heyer et al. (1994) describe a procedure for time-constrained searches
of amphibians, and note that variables such as time spent on the survey, and
using each collecting technique, number and experience of fieldworkers, topography and size (area) of site to be surveyed, local weather and climate, season, date and time of day all need to be considered and controlled for.
iii) For amphibians, the most efficient time to survey is usually at night. It
is useful, however, both in the interests of biology (it is possible to collect eggs,
larvae and adults in the daytime) and safety (it is easier and safer to move over
often difficult topography at night if you have seen it during the daylight hours)
to make a preliminary survey of the area to be sampled during the day.
Recording
i) The observer carefully records the time spent searching a particular
site; if more than one person is searching, it is important to record the number
of searchers.
33
ii) General information on the site should also be recorded, such as
heavy herb cover, any fallen logs present, etc. to give a picture of the situation
and to allow for possible later comparisons. A detailed habitat description of the
site is especially important.
iii) The number and species of animals encountered and/or captured is
recorded. Information on captured species should be recorded on the standard
form (Form 3.1).
iv) It is also important to note (in a notebook or on Form 3.2) the weather
conditions, phase of moon (if field work is done at night), habitat, number of
fieldworkers, time spent searching, etc.
v) For both reptiles and amphibians, it is often necessary to search by
turning over fallen logs, searching under bark, etc. The time spent using these
different methods by each worker is carefully recorded.
Data analysis
The time spent searching is multiplied by the number of searchers to
give the ‘total hours spent searching’; this, in turn, is related to the sightings per
hour. Time species counts may be used either to detect number of species or
the number of animals collected.
Advantages/limitations
This technique is probably best suited to sampling animals which are
fairly visible from a distance, and therefore not applicable for many forest situations except when amphibians have congregated for breeding. It may be useful
for reptiles that are ‘sit and wait’ predators, such as geckoes, which often
occupy relatively conspicuous sites at night; it may also be applicable for nighttime counts of chameleons.
3.3.8
Transect counts
Such counts might be used for conspicuous species, such as skinks,
which scuttle away from a path as an observer walks it. The transect methods
are discussed in Chapters 5 and 6. Jenkins et al. (1999) describe the use of a
modified line transect count method for surveying chameleons at night in
Madagascar.
3.3.9
Territory mapping
This technique can be used for lacertid lizards and for agamas, which
are markedly territorial. The locations of individual territorial males are determined and then plotted on a map of the study site. However, it is very timeconsuming and labour-intensive, and probably would be used only if you were
concerned with a particular species or population.
34
3.3.10
Sound recording surveys
Parker (1991) has argued convincingly for the use of tape recordings in
avifaunal surveys, and his arguments also hold for surveys of amphibians.
Tape recordings have been made of many frog vocalisations (Schiotz, 1999;
Passmore & Carruthers, 1995; Rodel, 2000); Heyer et al. (1994) suggest protocols for recording of amphibian calls. This technique is not applicable to reptiles, because none of the African species vocalise with sufficient volume and
regularity to be useful for such an approach. For additional information on
using sound recording surveys see sections 6.3.2.c and 7.3.9.
Equipment
●
●
●
●
●
high-quality portable tape recorder or mini-disc player
microphone and batteries
blank tapes or mini-discs
recorded tapes/CDs of frog sounds
plastic bag or similar for protecting equipment against moisture
Site selection
Tape recording may be conducted in the form of a general survey, or
sampling might be randomised to meet a particular experimental set up.
Remember that some anurans may be photophobic and thus may not call as
much or with the same intensity on a night with a bright, large moon as on a
dark, moonless night.
Procedure and Recording
i) Two approaches are possible. One is to record individuals as heard,
and try to approach and capture these animals for identification; preferably a
specimen with its field number noted on the recording of its call. A second
approach is to place the tape recorder at a particular site and record 5–10 minutes of the general calling sounds of amphibians. When recording species
which are sensitive to the approach of an observer/recorder, a useful approach
is to have a long microphone cable; the microphone is left near the animal
which has been vocalising, and the observer/recorder simply retreats to a
certain distance, and records using the long microphone cable.
ii) Give full habitat data, time of day, exact locality, name of surveyor, air
and water temperature, and other relevant details. Effectively, the tape is a
specimen, so it too must have as much precise data on it as possible. Long
periods of natural anuran sounds are valuable and lacking in most sound
libraries.
35
iii) A sample recording data sheet based on that of the Macauley Library
of Natural Sounds at Cornell University is provided (Form 3.3).
Data analysis
i) By collecting detailed data on individual as well as community vocalisations, a record is built up which will enable most species to be identified by
voice alone. Well-documented recordings also serve as valid records of a
species.
ii) Copies of these recordings should be deposited in a professionallymaintained sound collection where they will be available for researchers. Such
institutions include national museums, the British Library of Wildlife Sounds, or
the Macauley Library of Natural Sounds at Cornell University, Ithaca, New York,
USA.
Advantages/limitations
Because sound is so important in anuran biology, this technique adds
considerably to our knowledge of the species concerned. The human ear is
very fallible; the tape recorder, however, records all sounds (within the limitations of its microphone and the tape response), thus creating a permanent
record that can be assessed by others at a later date. It also permits identification of species that were not heard or seen by the recorder or other collectors,
and detailed sonographic study is possible in the laboratory.
3.4
Specimen handling
Given our rudimentary understanding about forest amphibians and reptiles, specimens are needed to allow accurate identification by experts, and for
future reference in the event of taxonomic revisions. Specimens that are collected, therefore, need to be preserved in an appropriate fashion (Knudsen,
1966; Broadley, 1973; and Heyer et al., 1994, provide detailed instructions),
and lodged in a suitable institution, museum or collection (see section 4.4).
The collecting of voucher specimens, or larger series of specimens
where necessary, also permits other data, such as reproductive condition, to be
assessed, and one can also obtain information important to population biology
(such as number of eggs per female). Careful labelling of specimens, with
cross-reference to field notes and photographs, is essential.
In addition to the whole specimen, many recommend that tissues of animals routinely be taken and fixed separately so that DNA may be analysed
later. Similarly, it is extremely useful to collect tissues fixed in such a way that
these may be used later for analysis of pesticides, metals, and other pollutants,
as has been done to assess insecticide spraying in Zimbabwe (Lambert, 1993).
36
3.5
Health and safety
Both amphibians and reptiles may harbour ectoparasites and endoparasites, and also may be infected by fungi and bacteria. While usually these have
been of little concern to those working with them, recently in some countries
there has been concern expressed that freshwater chelonians sold as pets
may carry the Salmonella bacterium and cause disease. It is therefore
advisable to take normal precautions when handling live animals as well as
dead specimens, such as using gloves and/or carefully washing hands with
soap and disinfectant.
All amphibians have a glandular skin and some of the secretions are
toxic and if ingested, potentially fatal. Most toads (family Bufonidae), for example, have specialised glandular areas on the skin, the secretions of which contain powerful toxins. Other anurans, such as members of the genus
Phrynomantis (formerly Phrynomerus) also secrete extremely irritating substances from their skin glands. Although in both the toads and other frogs
these substances are not usually a problem for those handling them, if the
worker has a cut or abraded area of the skin, irritation will result. Similarly, if
the secretion is transferred to the eye, nose or mouth, severe pain and irritation
may result (Howell, 1978). Simply rinsing with water or other diluting liquids is
the best first aid.
As ably described by Cansdale (1962) in his book on West African
snakes, and contrary to popular belief, very few people get bitten by snakes.
Those that do seldom suffer severe consequences – it is more likely that someone will be killed in a bus, or on a bicycle, than by a snake bite.
The venom of only a relatively few species is potentially fatal to humans.
Despite the low risks, however, it is still important to take precautions to avoid
being bitten by snakes, since surveying them does greatly increase contact.
Sensible, strong field boots (canvas, leather or rubber) are important, and can
be supplemented with thick socks and denim trousers for the areas between
ankle and knee (where most snakebites occur). Safety gloves (e.g. gardening
gloves) as well as a snake stick are important when catching and handling. In
the case of spitting cobras, which spray their venom at the eyes, safety goggles should be worn. All these precautions will reduce the chances of being
bitten by snakes.
In the unlikely event of a snake strike, every effort should be made, without risking further injury, to capture the snake (dead or alive) to show to firstaiders and medical staff. Snakes should be handled with extreme caution and
readers are strongly advised to learn to recognise the local venomous forms
and to avoid handling them. Details of venomous snakes and snakebite treatment can be found in Spawls & Branch (1995).
37
3.6
Conclusions
Our knowledge of amphibian and reptile biology and population cycles in
African forests is so rudimentary that substantially more survey work is needed
before forest management actions can be taken to reduce the risks of herptile
losses.
General surveys and pitfall traps are probably the first survey methods to
use at any site, supplemented with other methods outlined above where time,
resources, and interest allows. Until more specialists are trained, and more
funding is available for detailed studies on populations, biologists will continue
to carry out general surveys that indicate presence of amphibians and reptiles,
rather than the much-needed detailed population surveys and studies. Species
lists are useful, especially those which are annotated and provide information
on the conservation status of the fauna of an area. It is important for forest
managers to recognise when they have herpetofaunal assemblages of high
diversity and/or endemic, rare or endangered species of amphibians and
reptiles in their area. They can then encourage individuals as well as organisations with specialised training and experience to address the issues of amphibian and reptile populations in more detail than is currently the case.
38
3.7
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actuelles du genre de lizards Lygodactylus (Sauria, Gekkonidae). Dumerilia 2: 1–21.
Pitman, C.R.S. (1974). A Guide to the Snakes of Uganda. Revised edn. Wheldon and Wesley. 290pp.
40
Rodel, M.O. (2000). Herpetofauna of West Africa, Vol.1: Amphibians of the West African Savanna.
332pp, including CD.
Schiotz, A. (1999). Tree Frogs of Africa. Edition Chimaira, Frankfurt am Main, Germany.
Scott, N.J. Jr. (1982). The herpetofauna of forest litter plots from Cameroon, Africa. In:
Herpetological Communities. (Ed. N.J. Scott Jr.). U.S. Dept. Int. Fish Wild Ser. Wild. Res. Rept. No.
13: 145–150.
Spawls, S. (1978). A checklist of the snakes of Kenya. J. E. Afr. Nat. Hist. Soc and Nat.Mus. 3 (67):
1–18.
Spawls, S. & Branch, B. (1995). The Dangerous Snakes of Africa. Blandford, Cassell Group,
London.
Spawls, S., Howell, K.M., Drewes, R.C. & Ashe, J. (2002). A Field Guide to the Reptiles of East
Africa. Academic Press, London.
Stewart, M. (1967). Amphibians of Malawi. State University of New York Press, Albany, USA.
Stewart, M. & Pough, F.H. (1983). Population density of tropical forest frogs: relation to retreat
sites. Science 221: 570–572.
Vogt, R.C. (1987). Techniques. You can set drift fences in the canopy! SSAR Herp. Rev. 18: 13–14.
Waichman, A.V. (1992). An alphanumeric code for toe clipping amphibians and reptiles. Herpetol.
Rev. 23: 1992.
Western, D. (1974). The distribution, density and biomass density of lizards in a semi-arid environment of northern Kenya. E. Afr. Wildl. J. 12: 49–62.
Wyman, R.L. (1990). What’s happening to the amphibians? Conserv. Biol. 4: 350–352.
Yalden, D.W. (1977). The Identification of Remains in Owl Pellets. Occasional Publication of the
Mammal Society. Reading, UK. 8pp.
41
Form 3.1: Herptile Catch Records (instructions see p52)
Surveyor:
(total observers):
Field sheet ref:
Date:
(dd/mm/yy)
Altitude:
Aspect:
Address:
Survey site:
Latitude:
Longitude:
UTM (if available):
Vegetation:
Human disturbance:
Soil type:
Leaf–litter/ground cover:
Season:
Weather:
Lunar phase:
Temperature:
Other:
Trap line
& no.
Microhabitat
Water
Topography
association
42
Species and Other
specimen
sheet ref.
Form 3.2: Specimen Records: herptiles
Specimen sheet ref:
Field sheet ref:
Collector:
Date:
(dd/mm/yy)
Time:
Address:
Collecting site:
Latitude:
Altitude:
Longitude:
Slope:
Species:
Field no.:
Sex (if known):
Pregnant:
Eggs:
Breeding condition:
Additional notes:
Colour/markings:
Wounds:
Ectoparasites:
Endoparasites:
Measurements:
HB
TL
mm
mm
Material Preserved:
Skin
Skull
Skeleton
TV
mm
Snout-vent
mm
Other
mm
Stomach Faeces Blood
Stomach contents:
Component:
Percentage:
Remarks/Other
43
Age:
Liver
W
g
Kidneys
Form 3.3: Sound Recording Form
Species, Sound or Subject:
Recordist(s) and Address:
Date:
Time:
Weather:
Place:
Latitude:
Longitude:
Species/id
No. of individuals
Sex/Age
Breeding status
Sound Category
Response to playback
Notes:
For calls www.birds.cornell.edu
Contacts:
Curator
Library of Natural sounds
Corne Laboratory of Ornithology
159 Sapsucker Wood road
Ithaca, New York 14850, USA
www.bl.uk/collections/sound-archive/nsa.html
Curator
NSA Wildlife Section
The British Library
National Sound Archive
96 Euston Road
London NW1 2DB, UK
44
4.
Small mammals:
bats, rodents and insectivores
golden-rumped elephant shrew (Rhyncocyon chrysopygus)
Glyn Davies and Kim Howell
4.1
Biology
Small mammals are a disparate collection of flying and non-flying
species that have been grouped together because of their relatively small size,
despite obvious anatomical and ecological differences. In this chapter, we
consider three groups: rodents, bats, and insectivores (including elephantshrews). All groups are elusive and difficult to survey because, in order to avoid
predators, they have evolved dull colouration, secretive behaviour and, in many
cases, nocturnal habits. These characteristics, along with their small size,
make field identification difficult – a problem exacerbated by the very high
diversity of African small mammal species (for example, there are about 190
bats and some 380 rodents in Africa). These problems are no less acute for
insectivorous small mammals – there are about 165 African mainland species
(many of them in the genus Crocidura alone). Mammal lists of the world
(Corbet & Hill, 1991; Wilson & Reeder, 1993; Nowak, 1999), and regional
checklists, may help to give a rough idea of the species present in an area, but
only surveys and collecting carried out over different seasons will permit a
more accurate assessment of the species present in a given forest.
45
Bats (Order Chiroptera)
Bats are divided into two sub-orders: the fruit bats (Megachiroptera),
sometimes termed ‘megabats’, which use their large eyes and relatively long
noses to locate fruit and nectar/pollen food sources, and do not use highfrequency echolocation for navigation; and the insect-eating bats
(Microchiroptera), or microbats, which make use of echolocation and hearing to
find insects and small fruit foods, as well as nectar and pollen. Species from
both groups roost in the daytime, sometimes in large congregations, and are
most active soon after sunset, unless it is raining. Some are active during the
day as well as at night, and during the night different species may show activity
peaks at different times.
Rodents (Order Rodentia)
The rodents are usually divided into two sub-orders: the Sciurognathi,
which includes the squirrels, rats, and mice; and the Hystricognathi, represented in Africa by the porcupines, mole-rats, cane-rats and dassie-rat. Some
members of this diverse order are large (e.g. cane rat: 7+ kg; crested porcupine: 15+ kg) and all have powerful front teeth for gnawing. The mice and rats
mostly live in holes and forage for fruits, seeds, arthropods, etc. on the forest
floor, or under/along fallen logs. Most rats and mice are terrestrial, and most
squirrels are arboreal – however, there are some rare exceptions to this rule:
dormice and climbing-mice climb quite extensively in under-storey trees, while
some large squirrel species are ground-dwelling.
Insectivores (Orders Insectivora and Macroscelidea)
The insectivores belong to two mammalian orders: Insectivora, which
includes such diverse groups as the shrews, otter-shrews and hedgehogs, and
the Macroscelidea – the distinctive elephant-shrews (although there have been
recent taxonomic revisions). The shrews are distinguished from rodents by
their protruding snout, usually tiny eyes and elongated lower incisors. Most forage in leaf-litter for live arthropods and other invertebrates.
An important characteristic of small mammals is that many have the
reproductive ability to undergo large population increases during favourable
periods, and suffer substantial losses at other times. For species that show
these boom-and-bust cycles, estimates of population sizes are difficult to
extrapolate from year to year. There are also considerable differences between
different seasons, so surveys need to take careful account of this potential
bias; comparing dry season and wet season results will give a poor understanding of population differences between forests. There may also be differences in behaviour depending on weather conditions (e.g. mice sheltering
during rainstorms) and lunar phases (e.g. dark nights affecting fruit bat activity),
so these factors should be recorded during surveys.
46
4.2
Management issues
Small mammals, especially the more abundant species, are important
components of forest ecosystems. All small species are preyed upon, and
therefore support populations of many groups of carnivorous and omnivorous
mammals, birds and reptiles. Rodents that are not eaten are responsible for
the destruction of many plants’ seeds, but they can also play a key role in seed
dispersal; for example, when squirrels cache (hide) seeds in stores that they
fail to relocate before the seeds have germinated. Bats also play a very important ecological role in the forest, through pollination of flowers and dispersal of
seeds from fleshy fruits.
Small mammals may also be good indicator species of habitat change,
and some are pioneer species. Recent studies in southern Africa of small
mammals colonising disturbed coastal sand dunes have indicated the usefulness of rodents and other small mammals, as indicators (for example in regenrating coastal dune forests: Ferreira & van Aarde, 1997, and in central African
forests along logging roads: Malcolm & Ray, 2000).
In their relationships with humans, there are a number of rodent species
that do considerable damage to crops and stored grains, and fruit bats that do
substantial damage to soft fruits. As a result they are killed, often by trapping
rather than shooting, to reduce crop losses. An important by-product of these
pest control operations is bush-meat – including polythene-wrapped fruit bats
for sale in supermarkets (e.g. Mickleburgh et al., 1992) and road-side carcasses of cane rats (grass-cutters). Many other species have a neutral impact on
agriculture, and some are beneficial in pollinating fruit and vegetable crops.
Recent conservation reviews indicate that rodents (Lidicker, 1989), bats
(Mickleburgh et al., 1992; Hutson et al., 2001) and insectivores (Nicoll &
Rathbun, 1990) are all declining in Africa. In the case of fruit bats, disturbance
or destruction of roosting sites, over-exploitation of useful species and conflicts
with fruit-growers have been cited as the main causes of declines (Mickleburgh
et al., 1992). Schlitter (1989) listed some 67 species of African rodents (representative of eight families) as being of special conservation concern, while
Nicoll & Rathbun (1990) listed 58 species of insectivores, including six of the
15 elephant-shrew species, which need special conservation attention. For all
three groups, the most consistent cause of declines is modification, fragmentation and loss of habitats, especially forest environments (see the 2000 IUCN
Red List of Threatened Species (Hilton-Taylor, 2000) www.redlist.org, for recent
information).
Another consistent comment in conservation reviews is that very little is
known about these groups, either in terms of where they are found, or their
ecology and population biology (most work having been done in temperate
47
zones). In this chapter, therefore, a summary of basic survey principles is
given, along with an overview of the wide range of methods that have been
developed, many of which need to be adapted for particular species, or
particular forests.
4.3
Methods
General
The methods used vary according to the particular group; obviously, bats
must be surveyed using techniques which differ from those used for rodents.
Yet the general approach is similar and many of the factors to consider are
similar or the same. A first principle is to obtain the maximum amount of
information about an individual detected or captured. This may be a relatively
straightforward procedure when dealing with a specimen, but obtaining information on flying bats or rodents glimpsed only briefly is challenging to say the
least.
Identification
As mentioned earlier, many small mammal species can be very difficult
to identify, and sometimes it is only possible to identify specimens to the level
of genus. There are few field guides available to aid in the identification of
African small mammals, although Kingdon (1997) is an exception; however,
even this guide is limited in its discussion and representation of the smaller
mammal species. Regional works, such as Rosevear (1965, 1969), Happold
(1987) and Kingdon (1974), may be useful for identification, but they are all
hefty tomes and cannot be carried into the field. In most cases, identification
will need to rely on the use of identification keys, many of which are only available for individual families or genera and are not widely available.
Furthermore, the identification of small mammals, especially shrews and
rodents, to species level, usually requires a detailed examination of the skull
and teeth. This effectively means that some animals must be sacrificed to
serve as voucher specimens, and sent to museums outside of the region for
examination and study by specialists. Thus, the preservation of voucher specimens (at least 10 individuals of each sex per species) is a necessary and vital
part of any small mammal study.
However, a new effort aimed at students of mammals in Tanzania is just
bearing fruit. W. T. Stanley of the Field Museum of Natural History, Chicago,
Illinois, U.S.A., with financial support from the MacArthur Foundation, has
created a key to African mammals using either skulls or skins. While still in a
preliminary stage, this can be accessed at: www.devdirection.com/tanzania/
48
4.3.1
General surveys
General surveys can be used to start plotting the distribution of species,
in different habitats and at different altitudes, and to select sites for more
detailed investigation. All the information gathered during general surveys can
be mapped to show species’ distributions (section 6.3.1).
For bats, dusk-time walks near forest streams, potential roosting sites
(e.g. caves) and fruiting/flowering trees provide an indication of bat numbers.
Checking caves, hollow trees and fallen logs may also be rewarding, even in
the daytime. For rodents and insectivores, searching under fallen logs for runs,
where tiny feet have left a distinct path, as well as for signs of discarded food
remains or faecal pellets, may help identify sites that could be sampled later
with traps. In the case of elephant-shrews, spherical nests of grassy material in
the leaf-litter, as well as runs, are indicative of their presence.
Other indirect signs of small mammal presence include their teeth, skull
and other skeletal remains in owl pellets (regurgitated by owls underneath their
resting sites) and carnivore scats and skulls may also be found by searching
rubbish tips near villages (Barnett, 1992). Hair analysis is another useful
means of identifying small mammals indirectly; indeed, sampling of carnivore
scats in order to identify the remains of small mammal species is a proven
technique. In Central African Republic, Ray & Hutterer (1996) found that there
were 16 species of sympatric shrews in one 35km2 study area just by analysing
carnivore scats collected over a two-year period. They attributed this highly
unusual diversity less to some incredibly feature of the site, but rather because
carnivores, as a moving trap, represented a more efficient capture technique
than conventional pitfalls. With detailed information on hair size, colour and
structure (e.g. scale patterns), one can even design fur traps with sticky tape or
tiny snags placed on tubes through which animals pass, to enable the sampling
of hairs for subsequent identification to species.
For bats, high-frequency bat detectors can be used to investigate the
presence of insectivorous bats, and indicate where future trapping might focus.
However, a reference collection of bat calls is needed to relate the calls to a
particular species (see Wilson et al., 1996).
4.3.2
Bat roost surveys
When a bat roost has been located, there are two approaches that can
be taken to estimate the numbers present, namely emergence counts and
roost counts. The emergence points from caves, for example, need to be
located, and observers stationed at each in the late afternoon so that they can
count how many bats emerge at dusk. Each observer should have a watch and
49
tally counter. All bats exiting and entering should be counted in convenient time
units (e.g. five-minute intervals), and those that return to the cave (presumably
to come out again) are deducted from the total. Care needs to be taken to distinguish between different species leaving the same roost. This may be feasible
when only a few easily-distinguished species are present at a roost, but might
be extremely difficult or impossible when closely related species, similar in size,
shape and behaviour are present. If there are several hundred bats emerging
then counts become less accurate, and more observers (coupled with photographic techniques) can be used to improve the accuracy of the counts
(Barlow, 1999).
Counting bats that are roosting in enclosed areas (e.g. in buildings) can
be done using low lights and binoculars to make total counts, and tree-roosting
fruit-bats can be counted directly in the daylight (Kunz, 1988). As the colony
size gets larger, counting becomes more difficult, and sub-sampling of different
sections of the roost (with different concentrations of bats) may be needed. For
example, numbers of fruit bats in many trees may be estimated by counting a
sample of trees and multiplying up by the number of occupied trees once a
mean (plus standard error) number of bats/tree has been established.
4.3.3
Live-trapping: rodents
and insectivores
There are numerous reviews of this method of census (Delany, 1986;
Barnett, 1992; Wilson et al., 1996) and this section summarises the main
methods as they relate to forest survey work in Africa.
Equipment
●
●
●
●
●
●
●
string and flagging tape
specimen bags and polythene bags
sedation materials
gloves
equipment for marking animals
spring balances
traps (see below) and bait
There is a wide range of live-traps to select from (Fig. 4.1):
● At the smaller end of the range, Longworth and Sherman live-traps
are mostly made of aluminium, and measure approximately 230mm x
95mm x 80mm in size when set up. These traps are very lightweight,
and Shermans have the added advantage that they can fold flat for
storage and easy carrying in the field.
50
Fig 4.1: Live Traps
Havahart
Sherman
Longworth
●
●
●
●
Havahart live-traps (available from international suppliers) are effective
for sampling species such as African giant rat, and hyrax (dassie), and
are convenient and easy to use. However, they are not collapsible and
thus rather bulky.
Pit-fall traps are important to catch mammal species that may not be
caught in other types of live-traps. This includes species that do not
like the baits on offer and/or species that forage widely and do not
follow runs (including shrews and other insectivores). Shrews are
probably better surveyed using pit-fall trapping (section 3.3.2).
In the case of elephant-shrews, animals can be driven out of their
nests into encircling nets (2m-wide fishing nets), once the nests
have been located (see details on antelope drives – section 5.3.2).
The presence of nests along transect surveys has been developed as
an indirect index of abundance (Fitzgibbon and Rathburn, 1994), using
the same principles as described in the next chapter (section 5.3.3).
Site selection
i) Rodents tend to move around the edge of clearings, and beneath fallen logs and rocks. They also follow runs which may be visible, including along
low branches and lianas, and their holes are often at the base of trees and
rocks. They also use places to gather, store and consume foods, and to
shelter. All these are potential trapping sites.
ii) Once a trapping system has been developed, then every effort should
be made to keep the same site selection procedures, and the number and
types of traps consistent between different trapping periods (e.g. over consecutive years), or between sites in the same period. For example: 20% on lianas,
80% on the ground; 50% box traps, 50% break-back traps (see below).
51
Procedure
i) Traps are generally placed in clusters, termed ‘trap stations’, spaced
regularly (5–10m) along a transect or in a regular grid. Each trap station can
have a number of traps, although three per trap station is probably a minimum.
ii) The traps have to be baited, and particular attention needs to be paid
to standardising the baits. There are a number of baits that have been successfully used: peanut butter works well, and can be mixed with other items
(e.g. banana, maize meal, oats, raisins, forest fruits, chunks of manioc root,
dried fish, etc.). In Tanzania, KH uses pieces of fried coconut, mixed with local
peanut butter. This fits onto the trap bait-hook well, is attractive to rodents, and
seems to survive the threats posed by rain and ants. The selection of bait will
have a major impact on the species that will come to the trap, so the same bait
needs to be used if trapping is to be standardised between sites.
iii) If it is rainy, then some bedding (pieces of old newspaper) can be
added to the box traps to reduce the risk of hypothermia. However, care must
be taken in the process of preparing traps not to leave human scent which may
deter animals from entering – rubbing other smells (e.g. meat fat) onto the trap
is one option, but minimising handling and airing traps is always wise. If previous trapping has left urine or blood on traps, it is advisable to wipe/wash this
off. Indeed, it is good practice to thoroughly wash traps to remove old bait,
rodent urine, etc. prior to storage (see also the traps described in section 4.3.6).
iv) The traps can now be placed in suitable trap sites, and need to be
secured with strong string or stakes so that they are not moved either by
trapped animals or, on rare occasions, by predators trying to get to the trapped
animals. Trap entrances/surfaces should be flush with the substrate, so that
animals do not have to go uphill to be caught, and they must not be easily
flooded (or washed away) if there is sudden rain.
v) Mark each trap site with flagging tape, and give each trap, trapping
station and trap-line a unique number.
vi) The traps must be inspected in the early morning, midday and late
afternoon. If it is cold or wet, then more frequent inspections are advised.
Ideally standardise the procedure so that all traps are baited and set between,
say, 18:00 and 19:00, and are inspected between 06:00 and 07:00 the
following morning.
Recording
This section applies to all small mammals, including bats, caught in
live-traps.
i)
The following should be recorded on a standard trapping record
form (Form 4.1) at the beginning of each transect:
52
full name of surveyor; sheet reference, which could refer to the field
notes recording system (e.g. 3 or 12); date (dd/mm/yyyy); and address
of institution that has a copy of the field records and specimens collected; collector number.
● survey site: the name of the region/forest area, and site within the forest, where the survey was conducted (e.g. Kakamega Forest Reserve,
Ischeno area); altitude (in metres above sea level); aspect (e.g. is the
terrain steep or flat; valley-side, ridge-top or valley-bottom; facing
north, south, east or west); latitude and longitude, in degrees, minutes
and seconds (if available, using GPS), and the UTM (metric grid) can
also be added here (two letters, followed by six numbers).
● season: wet or dry season.
● lunar phase: what quarter of the moon is it, and is it getting larger
(waxing) or smaller (waning).
● vegetation: use terminology that is accepted internationally, in particular make use of White’s (1983) phytogeographic regions of Africa.
Other national and regional categories can also be used.
● any indications/signs of human disturbance.
● weather: a statement about the weather during the trapping period
(e.g. clear, clouds, rain, overcast, windy).
● temperature: typically the minimum night-time temperature.
Record all the traps that were set off during the night, making a
note of the following:
● trap lines/trap no.: the trap location can be cross-referenced to a map
of the survey site.
● trap type/bait: type of live-traps/nets or snap traps successful, and
what bait was used.
● microhabitat: this refers to details of the trap location – beneath a log,
at the base of a tree, on a low branch, in burnt land, tied to a liana, in
leaf litter, etc.
● water association: whether the trap is situated near water bodies (e.g.
5m from stream edge) and the type of water association (e.g. stream,
river, marsh, pond, dry river bed, etc.)
● topography: e.g. ridge top, halfway up hill, bottom of hill, valley, path,
plain, and so on.
● species captured and corresponding specimen sheet no (see iii). Use
the scientific name of the species where identification is certain and
record the English name where possible. Follow a standard list when
using Latin names.
● If the trap has been set off but no species has been captured, this
should be recorded under ‘Other’. Note whether bait has been
●
ii)
53
removed or partly eaten and if traps have been moved. If a species has been
captured, use the Other column to record information such as dominant plants
in the immediate vicinity or any other important observations.
iii) When an animal is caught, it is important to record as much information
about the animal’s condition as possible on standard forms (Form 4.2; occasionally, specimens may be collected for preservation purposes, see section
4.4).
iv) Care must be taken not to injure or traumatise the animals during this
process, and to minimise risk of disease or infection spreading to surveyors
(see section 4.5). Thick gloves are important, and surveyors should learn how
to hold captured animals without injuring themselves or the animals. Captives
can be sedated by carefully emptying the trap into a large polythene bag containing a small piece of cotton wool soaked in chloroform or ether. The animal
should be drowsy, but not unconscious, when it is picked up for inspection.
Data analysis is discussed in the subsequent section.
Fig 4.2: Handling small rodents
4.3.4
Live-trapping: bats
Although the same equipment will be required as for the live-trapping of
rodents and insectivores, the trapping system for flying mammals obviously is
entirely different. There are three basic bat-catching techniques:
Hand nets
Hand nets (made with mosquito mesh if necessary), with long handles, a
deep net, and firm rim can be used to catch bats. This can be done by holding
it over a small hole through which they are emerging, or placing them over
roosting bats on ceilings and cave walls (Barlow, 1999). Hand nets can also be
used to catch flying bats by bringing the net quickly around the bat from behind
(Wilson et al., 1996), although this method should be used infrequently
because it runs the risk of damaging the bat’s wings.
54
Mist nets
Mist nets for catching Microchiroptera should have a mesh size of about
36mm but stronger nets, with larger mesh sizes, are needed for
Megachiroptera. Mist nets come in varying lengths of 6–18m. Monofilament
nets should not be used for catching bats (Barlow, 1999). Discussions about
mist netting are given in the chapter on bird surveys (section 7.3.8), including
details of all the equipment needed.
Mist nets tend to be most effective in catching medium and large bats,
especially plant-visiting species travelling in the understorey of the forest.
Smaller insectivorous species tend to evade mist nets, and quickly chew their
way out when caught.
The advantage of mist nests is that the nets are easily transported in
bags to the field site, as long as large numbers of lightweight bamboo or aluminium poles are not needed. In addition, the surface area for catching can be
enlarged by stringing a number of nets together.
The main disadvantage of mist nets is that they are hard to move once
set up. It is also a slow and tricky business removing bats from the nets, during
which time both the bats and the nets can get damaged.
Harp traps
Harp traps have been developed in the last 30 years, and operate on the
principle that bats have difficulty in seeing – either visually or by means of
echolocation – thin strands (Kunz et al., 1996). They are most effective in
catching smaller, insectivorous bats.
To make a harp trap, a rectangular frame (approx. 2m x 2m) is constructed, and vertical lines are attached at the top and bottom, 25mm apart (the
harp). Monofilament fishing line (about 300g strength) is readily available for
this purpose, although steel wires have been used. A second frame, with the
same layout of lines, is fitted 70–100mm away from the first frame, with the
vertical lines on the second frame corresponding to the gaps between the lines
on the first frame (see Fig. 4.3). Bats fly into the trap and get blocked between
the two sets of lines, causing them to fall or flutter into a canvas bag at the
bottom of the trap. The canvas bag needs polythene flaps on either side of the
entrance, leaving an open slit through which bats will fall, and under which the
bats can rest in a dry place.
Trapping efficiency can be increased by having three or four layers of
lines on a single trap (Francis, 1989), and the traps can be made as large as
construction materials and access to forest survey sites allows; a trap used to
capture flying foxes was 15m high and 17m wide (Wilson et al., 1996). Some
traps have legs to stand them up on the forest floor, but others are hung from
tree branches using ropes and pulleys.
55
The advantage of harp traps is that they can easily be moved about to
other catching sites within the survey area, and bats can be removed from
them quickly. The disadvantages are that they generally offer a small surface
area for trapping, and can be bulky to carry into the forests in the first place.
Fig. 4.3: A harp trap
Site selection
i) For mist nets and harp traps, the entrance to roosts is an obvious
place to survey, although the roost exit should not be completely blocked and
care should be taken not to catch more bats than can be safely removed from
the nets/traps.
ii) Other suitable sites include beside, or stretched over, small pools and
streams, or any flyways that bats appear to be making frequent use of. The
best places are where there is a gap in the vegetation that funnels bats into a
narrow area where nets/traps can be placed. Placing traps/nets at right angles
to each other, or in a V-shape, may improve catches.
iii) Catching bats in the upper strata of the forest, or above the tree
canopy, obviously requires nets/traps to be hung from branches, or from aerial
walkways that have already been constructed. Time is needed to fire strings
into the canopy trees (with bows, cross-bows or sling-shots), and to haul up the
nets/traps in such a way that they hang securely and do not get caught up in
twigs and branches. Safety and specialist equipment are needed if climbers
are clambering up the trees to set the nets/traps.
iv) Bats learn to avoid places where traps/nets have been set, so
traps/nets need to be moved periodically (every 2–3 days), or as soon as there
is an obvious decline in the number of catches.
56
Procedure
i) Nets and traps should be set up well before sunset, so that they are
ready for the initial surge in bat activity at around dusk. In the case of mist nets
this means that any birds caught before dusk need to be removed.
ii) Nets and traps should be checked at least every 30 minutes. If too
many bats are being caught then traps/nets should be closed so that bats don’t
get damaged. They should also be closed if it starts to rain – bats die very
quickly if they get cold and wet.
iii) Although trapping efforts should be concentrated around dusk and
early evening, it is important to keep going throughout the night, or at different
periods on consecutive nights until dawn, in order to cover all periods of
potential peak activity for different bat species.
iv) Once a trapping/netting system has been established, it should be
kept consistent between survey sites and periods (e.g. same number and size
of nets/traps; same arrangement of traps/nets; same number of hours and
periods of the night sampled).
Recording
Follow the same procedures listed above for rodents and insectivores
(section 4.3.3; Form 4.1) being particularly careful while handling live bats.
Fig 4.4: Handling bats
Data analysis
This section applies to all small mammals, including rodents and insectivores, caught in live-traps.
At a most basic level, a list of the number of species caught can be used
as an indication of biological richness for those species that can be trapped.
Species lists can be built up over time, and supplemented with records from
other trapping/survey procedures.
Some rudimentary indices of abundance have been developed to make
use of trap records. These indices present data in terms of the trapping success for a given trapping effort, often expressed as catches per trap-night (trapnights = number of traps multiplied by the number of nights set), or catches per
trap-hour, etc. In the case of bats, reasonably accurate population estimates
can be obtained if a sample of 350–500 bats is caught (Barlow, 1999).
57
Advantages/limitations
i) For all but the largest species, there is little option but to trap small
mammals to carry out surveys. The constraints on this approach are the effectiveness of different types of traps to catch the full range of species present,
and the ease/difficulty of getting the traps into remote forest areas.
ii) At the level of generating a species list, the results reflect the presence of those species that are prepared to enter traps (for that bait). The
results are therefore limited to giving information on the species richness of
only those species for which the methods are suitable.
iii) The same applies for population estimates. However, once an effective trapping system (including trap-siting, bait, etc.) has been developed for a
species, then mark-recapture methods can be used to estimate absolute population densities, and make comparisons over time or between sites.
4.3.5
Capture, mark, recapture
If a long-term study is planned, then mark-recapture techniques can be
used to make better estimates of population size. In this approach, animals are
captured (using one of the methods described above), marked, and released,
and the population sampled again after some time, using the same trapping
methods. The population estimates are based on the equation:
Total population =
total first catch x total second catch
number of recaptured marked animals
However, a number of key assumptions must be met for this to follow
(after Kunz, 1988):
●
●
●
●
●
●
survival rate of marked individuals is representative of the
population as a whole;
the probability of survival between capture periods is equal for
marked and unmarked individuals;
the permanent loss of individuals from the population is a result of
deaths, and not long-term emigration (or dispersal);
marked individuals have an equal probability of being captured as
unmarked animals;
marks are not lost;
the intensity of trapping (number of traps, number of days trapping,
etc.) is the same in different surveys.
These requirements are often not met, especially during a general
survey of many species in a short period.
58
More detailed ecological research, with reference to other survey books
(e.g. Wilson et al., 1996), should be made before attempting this detailed level
of analysis. The references give details of the mathematics of the survey
approach, as well as different ways to mark animals before they are released
after capture (e.g. clipping rodent toenails; fitting bands onto bat forewings;
using luminous dyes and permanent markers on fur, etc.). Reference should
also be made to computerised data analysis systems, such as CAPTURE
(Pollock et al., 1990; obtainable from http//www.mbr.gov/software.html).
4.3.6
Removal or dead-trapping
Fig 4.5: Snap trap
Equipment
In addition to the equipment necessary for live-trapping (section 4.3.3),
the following should be borne in mind regarding the use of traps for
dead-trapping:
● Important considerations when selecting traps include: whether
their different parts are susceptible to rust, or rotting of wooden
parts; whether the spring is too strong, and is therefore likely to
destroy the specimens (loosening springs by one turn can resolve
this problem); whether they have serrated edges which can
severely damage specimens; whether they are too small to make
a clean kill of medium to large species.
● Rat-size traps take up space and are heavy. If packed in such a
way that they become bent or the triggers are damaged, they will
not be effective. It is therefore important to pack them as compactly and as securely as possible.
● When storing traps, metal traps can be painted with red oxide
primer to reduce rusting, and wooden traps can be dipped in linseed
oil, which reduces their tendency to soak up water in the field (and
increases trap life); as far as is known, the strong smell of this oil
has no negative effect on capture rate.
59
●
●
There is a wealth of locally-made traps which can also be used,
and which can improve the range of species being trapped in an
area. Although there are also local trappers adept at operating
these traps, the variability of trap construction usually precludes
using these traps for systematic surveys in different forests.
Try to select a type of trap which is available in large numbers and
which is likely to be available for purchase in the coming years.
Procedure and recording
The principles described above for live-trapping rodents and insectivores
(section 4.3.3) all apply to trapping with break-back traps.
Advantages/limitations
Break-back traps are much lighter and more compact to transport than
live-traps. The standard break-back traps used to kill pest species such as rats
(larger size) and mice (smaller size) are widely available, and can generally be
purchased in the country where surveys are to be carried out. They generally
catch more than live-traps, thereby providing specimens for identification and
museum reference collections.
However, they are indiscriminate in what they catch (i.e. they are not
species-specific); usually, many individuals of one or two common species will
predominate. Thus, many individuals are killed for a minimal amount of information that may be useful for management, a problem exacerbated when
doing surveys in conservation areas where protection may be a focus of management. The catch is also strongly influenced by the baits that are used, and
the ecology of the species in the forest site.
4.4
Specimen handling
Specimens collected from break-back traps can be supplemented with
those from live-traps. If an animal has been live-trapped, and examined, the
animal may be killed by cervical vertebrae dislocation, thoracic compression or
any other humane means. Barnett (1992) has offered some guidelines on when
animals might be killed:
● when the animal is injured (physically or mentally) in live-traps and
mist nets, including wet/cold animals that are hardly moving;
● to obtain reference specimens (voucher specimens) that can be used
for the later identification of species;
● where specimens of identified species are needed for reference
collections (for example, if it is found in a new region).
60
There is a wealth of information that needs to be collected from dead
specimens. Some of this can be done in the field, but further research may be
required back in the laboratory (Wilson et al., 1996). Since specimens are
required for accurate species identification, it is very important that surveyors
take time to visit museum or university specimen collections in order to become
familiar with hair/skin colouration, and other diagnostic features for species
identification, especially cranial/dental anatomy. Discussions should be held
with curatorial staff to get advice on what needs collection, how to measure
small mammals accurately, how to prepare specimens, and get copies of their
standard specimen record sheets and identification guides.
Equipment
●
●
●
●
●
●
●
●
dissecting kit: scissors (fine and thick), scalpel (including different size
blades), forceps (fine and thick), syringes (with fine and thick needles),
surgical mask and gloves
ruler/callipers
Pesola weighing scales
waterproof specimen labels
thick thread and sewing needles
plastic screw-top storage jars
muslin/paper towels
alcohol (70% ethanol) and/or formalin
Recording
i) Confirm the identity of the species and give the animal a field number.
Unless these are supplied by your institution, it will be most convenient if you
use a series of numbers that is preceded by your initials (e.g. CAM 305). Enter
this on the data sheet (Form 4.2) and, if you are not using pre-numbered label
tags, on a tag. A specimen without a label indicating the date, place of collection, and collector, has little value.
ii) It is critically important to use label paper that will withstand field and
storage conditions. If the specimen will be prepared as a study skin, standard
dry label tags are available. If it is to be preserved in fluid (formalin or alcohol)
then special water-resistant paper must be used for the labels. Furthermore, it
is critical to use either a hard pencil or waterproof ink (use either Indian or
Pigma felt-tip pen) on the label. If ink is used, make certain that it will not dissolve in the fixative. Be certain that it is completely dry before immersing it in
liquid. It may be necessary to dip the label in fluid first, and then dry it before
immersing the specimen.
iii) Examine whether the animal is male or female (if possible), try to
assess age (e.g. infant, juvenile, subadult, adult, old) from size and/or tooth
61
wear, and note other features such as: pregnant or lactating females; breeding
condition (i.e. is the vagina perforated); colour and markings (such as stripes
and spots, including variations); presence of wounds on ears, tail, and elsewhere; dental formula; mammary formula; and parasitic infections (collect specimens if required); etc.
iv) Take standard length measurements in millimetres: Head and Body
(HB); Total Length (TL); Tail Vertebrae (TV), Ear (E) and Hindfoot (HF) (see
Fig. 4.6). The hindfoot measurement usually includes the claw, i.e. HF/cu (cum
unguis) but a few workers measure the hindfoot excluding the claw (sine
unguis); we include the claw in our measurements. For bats, two additional
measurements may be used: Length of Forearm (FA), and Length of Tragus
(TR) – the latter is a prominence in front of the exterior opening of the ear.
Body mass in grams (W) is measured using a spring balance of the appropriate scale. Make a note of any material that is preserved (e.g. skin, skull, blood,
muscle tissue).
Fig. 4.6: Measurements for small mammals
Procedure
Proper specimen preparation in the field is necessary to ensure that any
mammal that dies, either as part of the process of collection for voucher specimens or incidentally by injury in a trap, being eaten by safari ants, or rotting in
hot temperatures, is preserved, labelled and the data used. A specimen is of
little value without a good label, so it is critically important to prepare your
specimens carefully and label them well.
Wet specimens
i) If the specimen is to be prepared as a fluid specimen (i.e. fixed in
formalin and later stored in alcohol) then a small numbered tag is usually tied
on the left hind foot.
62
ii) After the measurements have been taken and the number tag
attached, the body cavity is cut open using scissors or a scalpel; this allows the
fixative to enter the body cavity and gut as quickly as possible. If the animal
has a very full stomach, it may be necessary to inject formalin or alcohol into
muscle masses and into the stomach and/or intestine. Ideally, this is the time to
carefully examine the reproductive tracts of females and record the condition of
the ovaries and uterus, number of foetuses, and uterine scars.
iii) Because the skull is so critical to the identification of many small
mammals, some workers at this stage remove the skull from the carcass and
store it in 70% ethyl alcohol. The skull should be tagged with a small label
bearing the same number assigned to the animal, and kept with other such
skulls. Later, when dermestid beetles are used to clean the skull, they will happily devour the skin and muscle off such a specimen. Such is not the case for
material preserved in formalin, which the beetles do not seem to like the taste of!
iv) Information on what animals have been eating can be obtained from
the stomach contents, and other parts of the intestine or the faeces. The stomach contents should be analysed one by one, and proportions of volume attributed to different seasons (e.g. 50% seeds; 20% insects; 30% plant fibres).
v) Wrap specimens in muslin or paper towels before putting them into
the storage jars to reduce the risk of damage during transport. Make sure that
the preserving fluid is topped up and of sufficient strength; it is necessary to
have a large volume compared to that of specimens.
vi) If there is an opportunity to send tissue samples to laboratories for
genetic and cellular analysis, then the laboratory will give clear instructions
about how to prepare the samples.
Dry specimens
i) Small mammal skin preparation is a standard procedure, and involves
removing muscles and other tissues which are likely to rot, and stuffing the
body with material (such as dry cotton wool) so that the body retains a normal
shape.
ii) Skins need to be pinned out and dry on both sides, but they should
not be smoked (this will affect both skins and labels). Cover with cheesecloth to
keep flies from laying their eggs on the skins. Beware of potential predators,
such as insects, dormice, and other rodents, as well as birds of prey such as
kites and ravens; the latter have even been known to remove covers of tins,
etc. to get at specimens! Once skins have been dried (if they are sufficiently
dry, the skin will crinkle and the ears will be stiff) then they can be packed for
transport.
63
iii) Drying skins in forest conditions is very difficult as they are liable to
insect attack and rot very quickly. If wet specimens cannot be prepared, then
construct a drying oven using hurricane lamps and metal tins or buckets. This
will ensure that specimens are quickly dried, but care must be taken not to char
or smoke the skins. They can then be packed into plastic bags to prevent them
absorbing the damp, along with some naphthalene crystals (mothballs) to
reduce risks of insect attack.
iv) It is usual to preserve some specimens of each species as skeletal;
these have most of the large muscles removed, and are then dried. Or, if they
are in a very wet situation, as may arise in a rain forest, the skeleton can be
labelled and placed in 70% alcohol.
4.5
Health and safety
The close proximity of surveyors to small mammals during trapping work
means that care has to be taken to avoid the spread of infection or diseases.
Rabies is a risk in Africa, and there are probably many arboviruses (arthropodborne viruses) that might potentially be found in small mammals and their
ectoparasites. Plague, a bacterial disease transmitted by fleas, is endemic in
parts of Africa.
For these reasons, field workers should take care to avoid being bitten
by small mammals, and, if surveyors are bitten or scratched, lacerations should
be treated immediately with antiseptic and bandages. Even with dead animals,
care needs to be taken not to get scratches during specimen processing.
Always wear a face or surgical mask and protective gloves when collecting
trapped animals and preparing specimens (to avoid being bitten by any
ectoparasites, such as fleas, ticks and lice), or when doing carnivore scat
analysis (for indirect evidence of occurrence).
4.6
Conclusions
There is a wealth of methods that can be used, and adapted, in order to
survey small mammals. All require capturing the subjects of a survey, so a
combination of methods should be selected to ensure that those mammals that
avoid one method are captured with another.
64
4.7
References
Barlow, K. (1999). Expedition Field Techniques: Bats. Royal Geographical Society, London, UK.
Barnett, A. (1992). Expedition Field Techniques: Small Mammals (excluding Bats). Royal
Geographical Society, London, UK.
Corbet, G.B. & Hill, J.E. (1991). A World List of Mammalian Species. 3rd edn. Oxford University
Press, Oxford, UK.
Delany, M.J. (1986). Ecology of small rodents in Africa. Mammal Rev. 16: 1–41.
Ferreira, S.M. & van Aarde, R.J. (2000). Maintaining diversity through intermediate disturbances:
evidence from rodents colonising rehabilitating coastal dunes. Afr. J. Ecol. 38(4): 286–294.
Fitzgibbon, C.D. and Rathburn, G.B (1994). Surveying Rhynhocyon Elephant-Shrews in tropical
forest. Afr. J. Ecol. 32(1): 50–57.
Ferreira, S.M. & van Aarde, R.J. (1997). The chronosequence of rehabilitating stands of coastal
dune forests: Do small mammals confirm it? S. Afr. J. Sci. 93(5): 211–214.
Francis, C.M. (1989). Comparison of mist nets and two designs of harp traps for capturing bats. J.
Mammal. 70: 865–870.
Happold, D.C.D. (1987). The Mammals of Nigeria. Clarendon Press, Oxford, UK.
Hilton-Taylor, C. (compiler) (2000). 2000 IUCN Red List of Threatened Species. (Including CDROM). IUCN, Gland and Cambridge.
Hutson, A.M., Mickleburgh, S.P. & Racey, P.A. (Eds.) (2001). Microchiropteran Bats: Global Status
Survey and Conservation Action Plan. IUCN, Gland, Switzerland.
Kingdon, J. (1974). East African Mammals: An Atlas of Evolution in Africa. (Vols 2A & 2B).
Academic Press, London, UK.
Kingdon, J. (1997). The Kingdon Field Guide to African Mammals. Academic Press, London, UK.
Kunz, T.H. (1988). Ecological and Behavioural Methods for the Study of Bats. Smithsonian
Institution Press, Washington, USA.
Kunz, T.H., Tideman, C.R. & Richards, G.C. (1996). Capturing mammals: small volant mammals.
In: Measuring and Monitoring Biodiversity: Standard Methods for Mammals, pp 123–146. (Ed. by
D.E. Wilson, F.R. Cole, J.D. Nichols, R. Rudran, & M.S. Foster). Smithsonian Institution Press,
Washington, USA.
Lidicker, W.Z. (1989). Rodents: A World Survey of Species of Conservation Concern. IUCN SSC
Occasional Paper no. 4. IUCN, Gland, Switzerland.
Malcolm, J.R. & Ray, J.C. (2000). Influence of timber extraction routes on central African small
mammal communities, forest structure, and tree diversity. Cons. Biol. 14: 1623–1638.
Mickleburg, S., Hutson, A.M. & Racey, P.A. (Eds.) (1992). Old World Fruit Bats: An Action Plan for
their Conservation. IUCN, Gland, Switzerland.
Nicoll, M.E. & Rathbun, G.B. (1990). African Insectivores and Elephant-shrews: An Action Plan for
their Conservation. IUCN, Gland, Switzerland.
65
Nowak, R.M. (1999). Walkers Mammals of the World. 6th edn. John Hopkins University Press,
Baltimore.
Pollock, K.H., Nichols, J.D., Brownie, C. & Hines, J.E. (1990). Statistical inference for capturerecapture experiments. Wildl. Monogr. 107: 1–97.
Ray, J.C. & Hutterer, R. (1996). Structure of a shrew community in Central African Republic based
on the analysis of carnivore scats, with the description of a new Sylvisorex (Mammalia: Soricidae).
Ecotropica 1: 85–97.
Rosevear, D.R. (1965). The Bats of West Africa. British Museum (Natural History), London, UK.
Rosevear, D.R. (1969). The Rodents of West Africa. British Museum (Natural History), London, UK.
Schlitter, D.A. (1989). African rodents of special concern: a preliminary assessment. In: Rodents: A
World Survey of Species of Conservation Concern. (Ed. by W.Z. Lidicker). IUCN SSC Occasional
paper No. 4. IUCN, Gland, Switzerland.
White, F. (1983). The Vegetation of Africa. UNESCO, Paris, France.
Wilson, D.E. & Reeder, D.M. (eds). (1993). Mammal Species of the World: A Taxonomic and
Geographic Reference. 2nd Edition. Smithsonian Institution Press, Washington, USA.
Wilson, D.E., Cole, F.R., Nichols, J.D., Rudran, R. & Foster, M.S. (Eds.) (1996). Measuring and
Monitoring Biological Diversity: Standard Methods for Mammals. Smithsonian Institution Press,
Washington, USA.
66
Form 4.1: Small Mammal Catch Records (instructions see p52)
Surveyor:
(total observers):
Field sheet ref:
Date:
(dd/mm/yy)
Altitude:
Aspect:
Address:
Survey site:
Latitude:
Longitude:
UTM (if available):
Vegetation:
Human disturbance:
Season:
Weather:
Lunar phase:
Temperature:
Other:
Trap line
& no.
Trap type
& bait
Microhabitat
Water
Topography Species &
association
specimen
sheet ref.
67
Other
Form 4.2: Specimen Records: bats, rodents and insectivores
Specimen sheet ref:
Field sheet ref:
Collector:
Date:
(dd/mm/yy)
Time:
Address:
Collecting site:
Altitude:
Latitude:
Longitude:
Slope:
Species:
Field no.:
Sex (if known):
Pregnant/lactating:
Embryos:
Breeding condition:
Additional notes:
Age:
Colour/markings:
Wounds:
Dental formulae:
Mammary formulae:
Ectoparasites:
Endoparasites:
Measurements:
Bats:
FA
mm
TR
mm
E
mm
HF
mm
W
g
HB
mm
TL
mm
TV
mm
Material Preserved:
Skin
Skull
Skeleton
Stomach Faeces Blood
Stomach contents:
Component:
Percentage:
Remarks/Other
68
Liver
Kidneys
5.
Large and medium mammals
Helen Newing, Glyn Davies and Matthew Linkie
zebra duiker (Cephalophus zebra)
5.1
Biology
This chapter will concentrate on the ungulates and the carnivores. Some
species are sufficiently abundant in African forests to allow direct counting of
animals to estimate popuation sizes, but many others are rarely seen, and
therefore surveys rely on signs to assess their presence and gain a rough
index of their abundance. The signs include conspicuous footprints in soft
ground; large or persistent dung piles; diggings, and broken or trampled vegetation. This applies to many of the larger ungulates (see below), carnivores,
pygmy hippo (Hexaprotodon liberiensis), and the pangolins or scaly anteaters,
which live in burrows or tree-holes and feed on ants and termites.
Ungulates (Orders Proboscidea, Perissodactyla, and
Artiodactyla)
Forest ungulates (mammals which walk on the tips of their toes) fall into
two distinct size-groups. The small-bodied species (5-70kg) include duikers,
chevrotain and bushbuck, which live in well-defined, stable home ranges.
Larger species (>100kg) such as bushpig, giant forest hog, bongo, okapi, buffalo, rhinoceros and elephant are often wide-ranging or even migratory. In general, ungulates have a keen sense of hearing and smell, but their eyesight is
relatively poor.
Duikers are the most commonly seen terrestrial mammals in many
African forests, although daytime sightings all too often consist of a quick
69
movement and rustle in the bushes before you hear a whistle as they bound
away. Indeed, their shy and reclusive habit is one of the reasons why they are
so poorly studied. For many years they were thought to be a homogeneous
group of solitary, nocturnal, monogamous fruit-eaters, but research since the
1980s has revealed that they vary considerably in ecological characteristics
(Dubost, 1984; Feer, 1989). They have a varied vegetable diet including leafy
browse as well as seeds and fruits that fall to the forest floor. Some species
such as the blue duiker (Philantomba monticola) and the related Maxwell’s
duiker (P. maxwelli) are active during the day. Others such as the bay duiker
(Cephalophus dorsalis) are nocturnal, and the larger species (yellow-backed
duiker, C. sylvicultor; Abbott’s duiker, C. spadix and Jentink’s duiker, C. jentinki)
are active both by day and by night. Some species are solitary, some live in
pairs, and others have been recorded occasionally in groups with one adult
male and a number of adult females (e.g. Maxwell’s duiker: Newing, 1994;
Peter’s duiker, C. callipygus: Feer, 1989). All appear to have territories that are
marked with dung piles and musk from scent glands.
Large-bodied species such as suids (pigs), bongos, okapis, buffaloes,
elephants and rhinos have lower population densities than duikers. They may
also engage in seasonal migrations. Surveys of these species are therefore
based mainly on sign rather than direct sightings, as explained above.
Carnivores (Order Carnivora)
All carnivores range widely relative to their body size – the larger the
species the further they range – and they live at low population densities compared with the herbivorous mammals on which they prey. African forest carnivores range in size from the mongooses (300g to 5kg), genets and linsangs
(500g to 3kg), otters, and the African palm civet (3kg) to the civet (c. 15kg),
golden cat (c. 15kg) and leopard (c. 60–90 kg). Some open forest formations in
East Africa are also home to striped hyenas (c. 40kg). All carnivores have good
senses of smell, hearing and sight and are seldom seen as a result. Population
surveys of smaller species depend on trapping animals using fish and meat
baits (see previous chapter), whereas survey methods for larger cats include
recording pug-marks (tracks), scats, scrapes and kills, and the use of
photo-traps.
5.2 Management issues
There are a number of important management reasons to survey larger
mammals. From a conservation perspective, it is important to know how many
animals are in different areas so that management plans can take account of
migration routes and important locations for food or for refuge, as well as
70
identifying areas with concentrations of animals that have potential for ecotourism. Where animal populations are harvested, the effects of harvesting
need to be monitored to ensure that harvesting is sustainable. Furthermore
there are often conflicts between large terrestrial mammals and humans.
Solutions to all of these management issues need to be guided by information
from biological surveys.
At a time when deforestation is accelerating across Africa, survey information is particularly important to assess and monitor the long-term effects of
habitat changes. These range from complete loss of forest to minor vegetation
changes due to intermittent use. Forest clearance leaves fragmented islands of
forest containing small populations of ungulates that are often not viable in the
long term. In contrast, selective logging can create patches of secondary vegetation that benefit a large proportion of forest ungulates that are grazers or
mixed browser-frugivores (although a few species do appear truly dependent
on old growth forest).
Hunting and trapping heavily affect many forest species. Showy species,
such as leopards and bongos, are hunted for their skins. Forest elephants,
despite having smaller tusks than their savannah relatives, have long been
hunted for ivory. Duikers have been hunted and trapped for food for centuries
and are still the main source of fresh meat in many forested areas of Africa.
Hunting and trapping have increased dramatically over the past few decades –
partly because of rural population growth and partly because of increased trade
to supply growing markets in urban centres, facilitated by improved access
along logging roads. As a result, although the smaller duiker species reproduce
quite quickly, their populations have been eliminated from many forest areas
near large human settlements and roads (Wilkie & Finn, 1990; Muchaal &
Ngandjui, 1999; Noss, 1999); larger-bodied mammals reproduce the slowest.
In addition to human impacts on wildlife, large mammals can have a serious impact on humans. Elephants are major crop pests and the cause of frequent complaint from communities near forest areas. Forest pigs and buffaloes
also cause problems for farmers, especially in terms of trampling and digging,
and bushbucks eat vegetables in fields near villages. Leopards may prey on
goats, sheep and cattle. There must be a balance between wildlife conservation and the control of animal pests, and to accomplish this we need effective
monitoring of animal populations (Bell, 1984; Hill, 1998, 2000; Naughton et al.,
1999).
On a more positive note, large mammals are an important resource for
tourism development, and forest populations of elephants, bongos, rhinos, and
to a lesser extent buffaloes, can be attracted to waterholes and saltlicks near
lodges for high-quality tourist viewing. However, surveys and monitoring are
important to assess impacts of tourism on wildlife. A concentration of large
71
herbivores at waterholes can cause serious damage to the surrounding vegetation. Tourist trails can affect animal distributions in different ways – large
animals, such as elephants and pygmy hippos will actually use these trails,
because, like people, they find it easier than pushing their way through the
undergrowth, but heavy tourist use and inappropriate behaviour by tourists (or
by survey teams) may frighten animals away from the area. Conversely,
species that are hunted may congregate in areas where there are tourists,
because hunters are less likely to come there.
5.3
Methods
General
Mammal surveys can provide three levels of data for managers. At the
most basic level they can determine the presence or absence of different
species at different sites in order to build up distribution maps. Information from
such distribution surveys (see section 6.3.1) is most valuable for rare or endangered species or for species that can be used as indicators of forest condition.
At the next level of detail, simple sampling can be used to determine the relative abundance of a species at different sites, or at a single site over time. At
the third and final level, much more rigorous sampling, more extensive data
collection, and thus use of robust statistical analyses makes it possible in some
cases to arrive at a quantitative population density estimate.
Surveys of terrestrial forest mammals are hampered because many animal species are shy and secretive, hiding in the undergrowth. However, several
successful survey methods have been developed to overcome this problem for
some groups. They can be divided into direct methods, which are based on
sightings of the animals, and indirect methods, which are based on counting
their signs. The rest of this chapter describes the various methods and
indicates the strengths and weaknesses of each of them.
Seasonal variations in climate can result in dramatic changes in animal
behaviour, in visibility (according to density of undergrowth), and in the length
of time that tracks and signs remain visible. Therefore basic surveys to determine presence or absence of species may benefit from short visits in different
seasons, but any comparative studies should be restricted to a single season.
Identification
A number of excellent field guides are available for identifying the larger
mammals of Africa. Dorst & Dandelot (1983), Haltenorth & Diller (1984) and
Kingdon (1997) all provide detailed information on identification, distribution
and ecology. Other useful guides include Stuart & Stuart (1995, 1997) and
72
Estes (1991). Although not a field guide, Rosevear (1974) is a useful reference
for identifying West African forest carnivores.
5.3.1
Hunters’ calls, attractants
and observation points
Hunters traditionally use a variety of snorts, calls and whistles to attract
different species of animals. The best example is the nasal bleat used to attract
duikers, and researchers have used hunters’ calls to check for the presence of
different duiker species (e.g. Wilson, 1990). The results can be impressive:
within a few minutes animals will often come running to within a few metres of
the caller. This technique is most successful if experienced hunters are
employed to do the calling, and they should not be accompanied by more than
two surveyors. Calls should be made at distances of not less than 250m from
each other. The surveyors should position themselves in an inconspicuous
place, such as between the roots of a tree buttress, and remain still and quiet
while the hunter calls.
Other attractants include natural or artificial salt licks for herbivores and
meat or scent stations for carnivores (see Blum & Escherich, 1979, for the latter). It may take a few weeks for animals to find a newly-sited attractant, so
they are not suitable for quick, one-off surveys.
Equipment
●
●
camouflage-netting and string
machete, for construction of temporary hide
Site selection
Strategic observation points include: natural salt-licks, waterholes and
wallows, heavily fruiting trees, tree-fall gaps with a flush of new foliage, forest
glades, logging roads, and areas with regular signs of tracks.
Procedure
i) A simple hide can be built either with camouflage-netting hung
between trees or buttress roots, or by cutting the fronds of a palm tree to form
a see-through wall. In protected areas, check to make sure this is not prohibited. The hide should be located downwind of the observation site. Make sure
there is a comfortable sitting place so that you don’t fidget. Alternatively, rather
than build a hide, one can sit on a low branch in a tree or on a ridge or rocky
outcrop overlooking the forest floor below – few terrestrial mammals notice
stationary objects above their heads.
73
ii) Once a hide has been constructed it should be left for at least a day
before being used, so that animals become accustomed to it.
iii) The best time to start watches for most species is just before dawn
(so that you are settled down before the first light) or a couple of hours before
dusk. Approach the hide quietly from the opposite direction to the observation
site. Settle in a comfortable position so that you can keep still (use mosquito
repellent!).
iv) It is sometimes helpful to visit the ‘observation area’ to look on the
ground for footprints and other signs (hairs, dung, spoor, etc.), especially if
watches are not producing many sightings. This can be done in the midday
hours so that dawn and dusk watches are not disrupted.
v) A reasonable length of time for a first watch at a site is two to three
hours. Leave the hide quietly, and in the opposite direction from the observation area.
Recording
i) Fill in the survey data in the top section of the recording sheet (Form
5.1) before commencing the observation period. Give each survey site a name,
and give observation points within each site numbers or codes (e.g. Survey
site: Gouleako; observation point 3). Record the type of vegetation, the degree
of human disturbance (which you may know from archival information or from
direct observation), and any special features that may be relevant (e.g. riverine
forest, mature lightly-logged, many-fruiting figs). Include altitude if you are
working across an altitudinal gradient.
ii) When one or more mammals are seen, note the time and watch quietly for a few minutes, even if you can identify the species immediately. If they
remain at the site, begin to fill in the recording sheet (Form 5.1) very quietly
noting the time at the start of the observation, the species and the total number
of animals. Additional observations include the number of males, females and
young animals, if known, and their behaviour. Make a note of any food eaten,
and take a sample if necessary. If you cannot identify the animal species, write
a detailed description in your notebook including an estimate of height, the
shape (especially of the head and muzzle), horns (if present) and the coat pattern. Make a sketch of it.
iii) Remember to note down the time at which the animals leave. When
they have gone you can expand your observation notes and consult a mammal
field guide to check any species identifications you’re not sure about. Also
check the observation area for footprints, hairs, fallen fruits, etc.
74
Advantages/limitations
This is a time-consuming method, and should be undertaken only at
sites where there is evidence that animals are frequent visitors. Some skill is
needed in identifying suitable sites, and consulting local hunters and others
knowledgeable about local wildlife can save much time and effort. Within these
limitations, successful watches are a valuable and rewarding way to record the
presence of different species, to study behaviour, and to determine whether
sites hold any potential for regular viewing by tourists.
There are several potential negative impacts of longer-term feeding
sites. Animals may come to rely on being provisioned at the site, or they may
be placed in acute competition for the food at the feeding site. Alternatively,
hunters may learn of the site.
5.3.2
Net drives
Net drives are used both for traditional hunting, for example in the
Central African Republic (Noss, 1999) and Zanzibar Island (Archer, 1994); and
also by researchers to catch small deer and antelope (e.g. Bowland, 1990;
Newing, 1994).
There are inherent biases in the use of this method for determining population abundance. For example, radio-tracking has confirmed that Maxwell’s
duikers and red duikers sometimes move away from the nets or drivers before
they are observed (Bowland, 1990; Newing, 1994). Some duikers, especially
infants, will be missed because they freeze in thickets and are not flushed out
of their resting places. Nonetheless, net drives are sometimes the best option
to survey secretive ungulates, especially where thick vegetation makes direct
sightings difficult. The biases probably differ for different species, but can be
assumed to cause an underestimate.
Net drives can also be extremely noisy and disruptive, and there has
been some concern about impacts on resident animal populations. However,
evidence from radio-tracked animals has shown that they quickly return to their
territories and resume their usual activities once the drivers have departed.
Equipment/personnel
●
●
●
●
tape measure
hunting nets (e.g. 50m x 2m; mesh 25–50mm; dark-coloured, elastic,
ideally with a breaking strain of at least 100 kg)
60cm lengths of strong nylon cord attached to top of nets at intervals
of about 4m
machetes
75
●
large team (minimum of ten) of drivers/field assistants (with or without
hunting dogs)
Site selection
Within a survey site the region is stratified as described for transect surveys (see below) and sample units are selected to cover the full breadth and
range of habitats.
Procedure and recording
i) If experienced hunters are taking part in the survey, it is best to follow
their normal method (see Noss, 1999), since it is likely that they are successful
at finding animals. Hunters usually enclose a large area (typically 4–5ha) with
nets linked together.
ii) Where hunters are not involved the procedure will vary according to
the thickness of vegetation, the amount of netting available, and the numbers
and knowledge of field assistants/drivers. Each drive usually covers 0.5–1.0ha.
If the forest is quite easy to walk through and visibility is good, it may be sufficient to set up a single net-line immediately before the drive takes place, on
one side of the block to be searched. Where vegetation is very thick, a grid of
trails (50m x 50m) should be cleared a few days before the drive takes place.
This will allow the nets to be erected quickly and quietly and provide a sighting
line for the monitors. In thick vegetation, it is advisable to net at least three
sides of the drive area to make sure animals don’t escape unobserved. The
more nets used, the greater the time needed per drive, but the smaller the
number of people needed to monitor the edges of the block.
iii) At the beginning of the drive, the field surveyors should surround the
block to be surveyed as quietly as possible. The 2m-high x 50m-long nets
should be erected by tying the nylon cords to trees at a height of 1.5–2 m,
leaving enough slack on the ground to stop animals diving underneath. Once
the nets are up, people should be stationed along three sides of the block with
most people on the sides that are not netted, close enough to each other so
that they can see clearly along the whole length of each side. This will be a distance of between 15 and 30m, depending on the thickness of vegetation (they
usually need to be much closer together on the open sides). These people are
the monitors.
iv) The rest of the assistants form a line at one end of the block, opposite
a netted side. These are the beaters. Once the nets are set up, the beaters
enter the area and noisily dislodge animals from their hiding places by shouting
and banging trees, bushes and fallen logs with sticks. Dogs may also be used
for this purpose, but they must be kept under strict control at all times.
76
v) Some animals typically try to break back through the beaters, and so
beaters should be positioned closer together than the monitors (10–15m apart).
The more people involved, the larger the area that can be included in a single
drive. Depending on team size and conditions, each drive (including setting up
nets) can take anything from 30 minutes to two hours.
vi) Whenever an animal is detected the species and, if possible, age and
sex should be noted. The sighting is called out to the neighbouring monitors to
avoid animals being counted more than once. Any animals that are caught
should be restrained and examined, noting age/sex and condition. Specimens
may also, under certain circumstances, be collected (see section 4.4).
vii) At the end of the drive, the team comes together to compare observations and confirm the total number of animals of each species they have
seen. Basic information on the survey site, vegetation, weather and time of
drive should also be noted; Form 5.1 can be used, omitting the first and last
columns.
Data analysis
The population density is computed as the number of duikers counted
divided by the area of forest sampled during the drives. During fieldwork, the
cumulative density can be estimated at the end of each day of drives (by summing results from all previous drives), and a graph drawn to get an idea of
when the density estimate stabilises and sample size is sufficient.
Advantages/limitations
Net drives are only feasible if a large labour force can be organised and
transported for a few days to the survey sites. If this is possible, the method
gives a large number of direct sightings and offers one of the most accurate
ways of getting population information for management purposes. In areas of
thick, secondary vegetation, it is sometimes the only option for surveys of terrestrial mammals.
5.3.3
Survey walks: reconnaissance
and transect
The use of observation points or net drives is most suitable for concentrated surveys in small areas of forest. To survey a larger area with relatively
small survey teams (two or three surveyors) the only realistic option is to carry
out survey walks through the area. Survey walks are used in two ways: either
for a ‘quick and dirty’ first assessment (a reconnaissance survey), or for a more
methodical evaluation of relative abundance or population density, through the
use of carefully positioned transects (straight trails). They can be based on
77
either direct encounters with animals or indirect signs (footprints and dung –
see section 5.3.4). It is not possible for a single surveyor to search thoroughly
for both at the same time, but different members of the survey team can
concentrate on different aspects in order to maximise data collection from each
study site. Surveys should be carried out by night as well as by day, because
a) nocturnal species will be seen that otherwise might remain undetected; and
b) many diurnal species such as blue and Maxwell’s duikers freeze when
caught in the beam of a strong torch, thereby allowing the surveyor to determine age and sex of individuals.
To carry out transect surveys, new transects should be cut that are carefully located in order to sample different vegetation types and levels of human
disturbance in proportion to their estimated occurrence in the study area. The
perpendicular distance of each animal or group of animals (or each dung pile
or group of piles) from the centre of the transect is measured, so that an estimate of population density (or dung density) can be made. For population estimates, a minimum of 40 sightings per species in each habitat is necessary, and
ideally over 100 sightings should be used (Plumptre, 2000). Therefore, transect
surveys can only generate population estimates for species that are seen relatively often. In practice, sightings of all species are recorded, and different techniques are used to analyse data for each species, depending on the amount of
information gathered.
The procedure for reconnaissance surveys is similar to that described
below for transect surveys, but with two major differences – firstly in the sampling, and secondly in the lack of recording of perpendicular distances from the
transect. Reconnaissance surveys differ from transect surveys in that they ‘follow the line of least resistance’ through the vegetation in order to cover as
much ground as possible. They may use existing human or animal paths, follow streambeds or concentrate in areas of sparse undergrowth where it is possible to walk in a straight line without clearing vegetation (Walsh and White,
1999). They consist simply of recording all encounters with animals and sign
for a given distance walked. Vegetation types and levels of human disturbance
can be recorded during an initial reconnaissance survey.
Equipment/personnel
To set up transects
● 30m tape-measure or topofil (hip-chain)
● fluorescent vinyl flagging tape & marker pens
● two machetes
● team of four or more people (including two or more line-cutters)
● maps, GPS, altimeter and clinometer if you are also undertaking
mapping
78
To carry out transect surveys and reconnaissance surveys
● one or, at most, two people
● optional: optical range finder or survey laser binoculars
Site selection
i) As a general rule, transects should cover the main habitats present in
the same proportions as they occur in the study area. For studies in undisturbed forest, this is usually done by using the bottom of the valley as the main
axis and cutting transects perpendicular to it. For surveys of very large areas, a
series of baselines can be cut parallel to the valley bottom – for example, at
intervals of 5, 10 or 50km – and transects can be cut perpendicular to each
baseline. Transects should be a minimum of 2km apart (preferably more), and
should not cross each other. (See White & Edwards, 2000, Chapter 3, for further discussion of stratified sampling).
ii) Surveys that aim to determine the abundance of animal populations at
the regional level must usually include areas with different levels of human
activity and habitat disturbance (farmbush, secondary forest, logged forest,
undisturbed forest). If disturbance is likely to have a greater effect on mammal
populations than watersheds (for example, where hunting or farming is very
intensive), it is more appropriate to use a road as the primary axis or to balance sampling according to the distance from human settlements (e.g. Lahm et
al., 1998).
iii) Once the approximate survey areas are decided, transects should be
positioned at least 300–500m apart and at least 500m from the base camp,
because camp noises and smells often deter mammals (unless they are
searching your rubbish for food!).
iv) Large animals may use existing paths, so new paths should be cut for
surveying in order to ensure random sampling. However, cutting paths during
surveys would frighten the animals away. As a compromise, new transects can
be cut a day or so before beginning the survey. If the cutting of new transects
is not felt to be justified and old paths are used, it is better to use narrow trails
than wide tracks.
v) Using existing trails and roads is an efficient and useful way to check
for the presence of species. However, using long-established trails that hunters
and trappers follow, or logging tracks which have very different vegetation to
the rest of the area, will seriously bias survey results and influence population
estimates.
Procedure — cutting transects
i) Use a random number table to select a starting point and direction
(left or right) from the baseline for each transect. Alternatively, select the
79
transect direction to pass through habitats of survey interest. The choice of
options will depend upon the overall aims of the study and the degree of habitat specialisation of the animals you are surveying. Each transect should be of
a length that can be traversed in a single session (typically 3–5km).
ii) Each transect should be cut perpendicular to the baseline, using a
compass to keep it straight and the 30m tape or hip-chain to record the distance cut. Slight detours around obstacles such as tree-falls are acceptable as
long as the original direction of the transect is maintained. If the vegetation is
thick, two people should take turns at cutting. Record special features (hunters’
camps, streams, etc.) as they are encountered, so that they can be mapped
immediately.
iii) Cut only the minimum vegetation necessary. If transects are going to
be used only during the day for a period of weeks, it is necessary only to make
the slightest clearance to allow movement through the area following a compass bearing (e.g. Walsh & White, 1999). If they are to be used at night, they
must be visible enough so that they can be followed easily without distracting
from the search for animals during night censuses. If a long-term study site is
being created, trails should be cleared sufficiently so that they will need only
minor maintenance.
iv) Mark the distance along the transect every 50m. If transects are only
going to be used for a few months, write the distances on pieces of fluorescent
vinyl marker tape and tie to saplings by the side of the path. If permanent transects are being set up, paint the distances on trees, or nail numbered aluminium tags to tree trunks.
v) Allow newly cleared transects to rest for at least one whole day
before beginning surveys. This will let animals recover from the disturbance
and return to their normal haunts and habits. This is also a good time to draw a
sketch map of the transects.
vi) As a precaution against opening up new areas of forest for hunters
and trappers, the starting point of a transect may be disguised so as not to
draw attention to the new path, or may be started 50m inside the forest (from
a road or logging track). Some surveyors even cut transects with secateurs so
that no path is left after them. If the transect is not going to be re-used, all distance markers should be removed at the end of the survey period.
Carrying out surveys
i) Daytime surveys should preferably be carried out in the mornings from
just after dawn to about 11:00, when animals are most active. If time is short,
additional afternoon censuses can be carried out between 15:00 and 17:30,
after which visibility becomes very poor. Night-time surveys can be conducted
at any time during the night, but 20:00 is a common start time.
80
ii) Do not carry out surveys in the rain: it will be harder to pick up
sounds, and will affect the behaviour of animals (and surveyors!). If it begins to
rain, pause the survey until the dripping stops, or if it seems to be likely to
continue, discontinue the survey.
iii) Ideally, transects should be walked by a single observer in the daytime, or by two observers at night. Walk very slowly, looking from side to side
for movements and listening intently for sounds in the undergrowth, animal
calls or gnawing sounds. Aim for an average speed of about 1km per hour,
including a pause every 100m or so to stop and listen. Additional time will be
taken to record data when animals are sighted. Each transect should therefore
take between three and five hours.
iv) Accurate distance estimation is essential, and the use of an optical
range finder is recommended (see also section 2.5).
v) If possible, rotate observers between transect lines to cancel out idiosyncratic differences. It also makes it more interesting and gives everyone the
chance to see unusual tracks and signs, which can be marked with fluorescent
tape.
Recording
i) At the start of each transect walk, fill out the top part of the form below
(Form 5.2). When one or more mammals are sighted (and often this will be of
animals in flight), complete the columns in the second part of the table.
ii) The perpendicular distance is taken from the position at which the animal was first detected to the nearest point on the transect, thus it may be necessary to walk along the trail to reach the correct point. It also may be necessary to approach the animals quietly in order to get a clearer sighting.
Additional observations can include the number of males and females, and
presence of infants, activities and behaviour, and association or interactions
with other species.
Data analysis
i) Relative abundance: for species where sample sizes are too small to
allow estimates of population density to be made, the number of animals
encountered per kilometre walked gives a rough indicator of abundance.
ii) Estimating population densities from line transect censuses involves
complex mathematical modelling of the likelihood that animals are detected at
different distances from the transect. However, these statistical analyses can
be executed by the custom-made computer program DISTANCE, which is
downloadable from the internet (www.ruwpa.st-and.ac.uk/distance) and should
be used in conjunction with the accompanying book (Buckland et al., 1993).
81
Analysis rests on several assumptions:
● that transects are placed randomly with respect to the distribution of
animals;
● that all animals on the line (strip width) are always detected;
● that animals are detected at their initial location, i.e. prior to any
movement in response to the observer;
● that measurements of perpendicular distances (animal-transect,
observer-transect) are exact.
It is rarely the case that all of these assumptions are met perfectly, which
means that population estimates must be treated with some caution. For a full
review of the key issues on theoretical aspects of analysis, and how to deal
with discrepancies, see Buckland et al. (1993).
Advantages/limitations
The main advantage of reconnaissance surveys is that they are quick.
Also, they can be carried out during routine activities such as patrolling by park
guards, so lend themselves to monitoring. The main disadvantage is that samples are likely to be biased in terms of habitat and intensity of human use.
However, some studies of elephant dung and gorilla nests have compared
results of reconnaissance surveys and full transect surveys and have found a
high level of correlation. The general rule is that recce surveys should be
backed up by some formal transect surveys in order to evaluate any biases
(Walsh & White, 1999; White & Edwards, 2000, Chapter 13).
5.3.4
Indirect methods
When the survey subjects are not seen directly, or seen very rarely, then
indirect survey methods are needed. This means that surveys are made for the
signs left by the animals, and the population density of the animals producing
the signs is estimated. Signs include faeces (e.g. pellet piles of duikers, dung
piles of elephants and buffaloes, scats of cats), footprints or spoor, hairs, diggings and nests (for pigs), urine-marking sites (pygmy hippo, rhinoceros and
carnivores). In this section, attention is focused on three approaches: dung
counts, track counts, and photo-traps.
A. Dung counts
Animal population density can, in theory, be calculated from dung density
on the forest floor according to two variables:
● The number of dung piles produced per animal per day (defecation
rate).
● The length of time the dung takes to disappear (dung-decay rate).
Unfortunately these two variables are affected by several different factors, and
82
this introduces many potential sources of error. In addition, for groups such as
medium-sized duikers or small carnivores it is difficult to identify dung to
species level. For example, only biochemical techniques will enable identification between the scats of golden cats and mongooses. Defecation rates vary
with diet (e.g. White, 1995), and, in the case of big cats, with the oestrous
cycle of females. Decay rates vary with the weather, microclimatic conditions,
and with dung beetle activity. In Ugandan forests, for example, Nummelin
(1990) showed that duiker pellets were encountered less frequently when rainfall was high prior to surveys.
Any errors in estimation of decay rate and defecation rate will have a
radical effect on the estimation of population density (Plumptre, 2000).
Furthermore, territorial species such as duikers and carnivores use droppings
to mark their territories, so distribution of dung is not random, presenting complex sampling problems. In the case of migratory or far-ranging species such
as elephants, the survey area may not cover their whole range, so dung density will vary according to the passage of elephants through the survey area in
the period prior to the survey.
However, in spite of methodological difficulties, dung counts may be the
best option available for surveys, since dung is the most frequently encountered sign of many larger forest mammals. In an effort to address the constraints, detailed techniques have been developed to use dung counts for surveying forest elephants (Barnes and Jensen, 1987), and similar methods have
been used for species ranging from buffaloes to duikers. If dung density is very
high, it may be possible to do away with the need to consider decay rates by
surveying the same transects repeatedly and clearing them of dung after each
survey. The number of piles produced for the unit area surveyed within a
known time period (i.e between the two consecutive surveys) can then be
recorded (Plumptre, 2000).
For elephants, density estimates from dung counts have been shown to
correlate well with those from other methods (Barnes, 2001). In general, however, the smaller the species the less useful the method, because decay rates
are much more variable (see Plumptre & Harris, 1995, for discussion of
methodological issues). For this reason, dung counts for smaller species
should only be used with caution for a first indication of relative abundance.
Equipment/personnel
●
●
●
●
30m tape-measure or topofil (hip-chain)
steel tape-measure (1 mm gradations)
fluorescent vinyl marker tape and marker pens to mark distances, or
more permanent numbered aluminium discs, hammer and nails
team of four people
83
Site selection
Most aspects of site selection are the same as those for transect surveys
(section 5.3.3.). However, new transects should be used for dung transects.
These may be along newly cut trails or may simply be unmarked survey routes
following a compass bearing.
Procedure
i) It is advisable for every study to begin with dung decay trials to determine the length of time dung piles remain on the forest floor (but see ii below).
To do a decay rate trial, at least 50 fresh dung piles should be located and marked.
For elephants, each pile should be visited once a week and its state of decay evaluated according to the categories on Form 5.3. In north-east Gabon, an average
decay rate for elephant dung was calculated at 2.4% per day, with individual dung
piles lasting from a few days to many weeks (Barnes & Jensen, 1987).
ii) Barnes et al. (1997) showed that decay times for elephant dung are
inversely related to rainfall in the month of deposition, and dung densities are
affected by rainfall in the previous two months. However, this varies between
different geographical areas (Nchanji & Plumptre, 2001). Therefore, unless
detailed baseline studies have been done in a given country or region, further
surveys are necessary to estimate decay rates and calculate dung density per
elephant (see Form 5.3 notes on elephant dung decomposition states).
iii) The principles and procedures for dung surveys are similar to those
explained for transect surveys in the previous section (section 5.3.3).
iv) During dung surveys, one person should search the ground for dung
piles while the others maintain the compass route, measure the distance
walked, and cut a path. The searcher should advance slowly, scanning the
ground from side to side. This takes a lot of concentration, and a different
member of the team should take over as searcher every 250m or so. It may be
worth surveying shorter distances (subsamples of the main transect) more
slowly and carefully for the pellets of smaller species (e.g. duikers), at least for
presence/absence data.
v) For leopards and many other carnivores, cutting a transect through
the forest will yield little information, and it may be best to survey along roads
and trails. Distances can be measured by routing on a GPS.
Recording
i) When a dung pile is detected, record the distance along the transect
(with the 30m tape or hip-chain), the perpendicular distance from the centre of
the transect to the centre of the dung pile (with the steel tape-measure), the
state of decomposition of the boli (the individual spheres of dung), and the
vegetation type at that location. See Fig. 5.1
84
Transect route
ii) You can also record tracks
encountered incidentally on the
same sheet (Form 5.3), putting
track measurements and other comments in the general observations
column.
a
b1
Fig. 5.1: Dung counts
Transect measures for pellet/pile
counts. Measure the perpendicular distance from the centre of a duiker pellet
pile to the transect (a). For elephants,
piles may be more dispersed and need
to be measured in two ways: i) pile clusters on one side of the transect should
be measured to the outer (b1) and inner
(b2) limit, these added together and then
divided by two; and ii) for a dispersed
pile on either side of the trail, measure
the outermost perpendicular distance on
either side (c1 & c2), then subtract these
two distances and divide by two (after
White & Edwards, 2000).
b2
c1
c2
Data analysis
i) Calculating the width of the survey transect is done as for sighting
transects (above), using the perpendicular distances from the trail to each pile
detected (in the case of elephants, excluding E state bolus piles, Barnes &
Jensen, 1987). The mathematical calculations used to assess the variable strip
width are complex but can be done using the computer program DISTANCE
(section 5.3.3.). If possible, a minimum of 100 dung piles should be recorded
(Plumptre, 2000), and the absolute minimum for this method of analysis is
generally taken to be 40.
ii) The area of the transect is calculated as length multiplied by width,
and the density of droppings as the number of dung piles divided by area.
iii) Once dung density has been calculated, figures are required for defecation and decay rates. Unless you have been able to calculate a defecation
rate, use a standard rate of 17 boli/day for elephants (based on Wing & Buss,
1970). For duikers the situation is more problematic, because it is unlikely that
defecation or decay rates will be transferable between different species, forests
or seasons, and few have been studied (Koster & Hart, 1988).
85
Short-cut method for elephant dung counts
In an effort to reduce the time needed for detailed surveys, Barnes
(1988) describes a short-cut method, whereby an observer follows a compass
bearing without cutting a trail, and records the presence of all elephant dung
piles (decomposition states A to E). At the most basic level of analysis, the proportion of 500m sections along the transect which contain dung is fitted to a
calibration curve established during more thorough research efforts, and the
dropping density (piles/km2) read from the graph. The same data analysis procedures as described above are then used to derive population estimates. This
is a very coarse-grained method of estimating densities. However, as with
reconnaissance surveys, the advantage is that a great distance can be covered
relatively quickly. It provides distribution data and gives some indication of the
relative importance of different areas for elephants in different seasons.
Fuller use has been made of field data (the recce method) in elephant
surveys in Gabon. Unlike in the full method described above, distance to each
dung pile was not measured, but estimates were made from the number of
piles/km. This method is obviously less accurate, but it can cover about four
times more ground than the full method above (with the same effort). Walsh &
White (1999) suggest using both methods, and calibrating different estimates.
B. Track (footprint) surveys
Footprints or spoor (e.g. tracks of duikers, pug-marks of cats) give vital
information on the presence of species, including those that are rare or hard to
spot, and can be carried out alongside other types of survey work. However,
this method is less robust than dung counts for estimates of relative abundance
because track densities are affected by the type and dampness of the soil substrate, rainfall, and the movement patterns of animals through the survey area.
Also, track size and shape change with the animal’s gait, the soil substrate,
and the age of the track. Fresh tracks in an ideal soil type have well-defined,
vertical edges, making it relatively easy to measure them accurately, but most
tracks found will show some degree of spread as they fade. Edges become
sloped and poorly defined, making measurements difficult.
As a result of these variables, similar-sized species are hard to distinguish from their tracks. Also, young animals leave tracks that resemble those of
adults from a smaller species (e.g. tracks of young red duiker resemble those
of adult blue duiker). Some traditional hunters have been reported to be able to
distinguish the tracks of all species (Koster & Hart, 1988), but, so far, biologists
have been unable to come up with objective methods to do this, and most track
surveys lump forest antelopes together into two or three size categories.
Species identification is less of a problem for cats since only the leopard and
the golden cat are present in forests, and they are very different in size.
86
If it is possible to distinguish individual animals by their tracks, an estimate of population density can be made. Stander (1998) succeeded in doing
this for leopards in a semi-arid environment, with the assistance of experienced
San hunters and the advantage of being able to survey large distances from
vehicles (he only found an average of one spoor each 38.1km). However, as
with distinguishing ungulate species, biologists have found it very difficult to pin
down an objective methodology (see also Smallwood & Fitzhugh, 1993).
Equipment
●
●
●
●
ruler (marked in mm)
hand-rake
for tracing prints: sheets of acetate or glass and marker pens
for making casts of prints: plastic drinking straws, talcum powder,
plaster of Paris powder, mixing container, stirrer, paper casting frames,
water, scalpel/sharp knife, and fine brush. Vinegar can also be used to
make casts set faster
Site selection
Site selection can be:
i) Opportunistic – wherever tracks are seen.
ii) Strategic – search any area where there is a damp, soft or sandy
damp substrate which will take an impression of a light footprint. Ideal places
include damp, sandy or dusty areas on roads and paths and sandy stream
beds (in the dry season) or river banks.
iii) Systematic – set up track stations at regular intervals (e.g. every
50–100m) along a transect. Clear all leaves and debris and rake the ground so
that it is smooth and soft enough to take animal footprints (e.g. Wilkie & Finn,
1990).
Procedure and Recording
Site features and track details for different species/mammal groups
should be recorded on Form 5.4 (see White & Edwards, 2000, Chapter 10, for
more detail). These measurements should be taken for up to three footprints of
the same animal if possible. If unsure of the mammal group, make a sketch
indicating scale and dimensions measured. Tracing onto acetate or glass
sheets makes identification of individual cats from pug-marks easier (Panwar,
1979).
87
Identification
There are very few field guides that give details of footprint size and
dimensions for larger terrestrial mammals. Walker (1991) is a noteworthy
exception, but covers mostly savannah mammals. Stuart & Stuart (1995, 1997)
may be helpful for people working in East Africa, while the books by
Liebenberg (2000), although restricted to southern Africa, may prove useful to
anyone trying to master the art of identifying mammal or other spoor.
Fig 5.2: Footprints
bottom: leopard & blue duiker, top: bushbuck
& civet.
The basic footprint measurements (in mm) are length
and width – as shown on the
figures. For carnivores, length
of pad and claws should be distinguished, and for larger carnivores the length and width of
the large heel should be measured (note if claws included).
Length and width of toes can
also be taken.
Where possible, tracks of
captive animals should be measured (e.g. in zoos) to get a
clear idea of footprint shapes
and sizes. One study of
antelopes in the West African
Table 5.1: Footprint lengths of species in West
African forests
Max length (mm)
Species
80–100
Bongo
50–75
Large duikers
(yellow-backed, Jentink’s, Abbot’s)
18–45
Bushbuck (30–45mm), medium/small,
duikers, chevrotain
Below 18
Dwarf antelopes (Neotragus spp.)
88
forest zone (Newing, 1990), distinguished four, clear footprint size classes
(Table 5.1). In addition to the species listed below, tracks of the sitatunga are
distinctive because of their very long, splayed hooves.
Taking permanent records of tracks
When unusual tracks are found and cannot be identified immediately, it
is worth taking a record for identification back at base camp for future work.
This can consist of a photograph, a tracing of a footprint, and/or a plaster of
Paris cast.
The first step is to carefully clear any obvious debris obscuring the outline of the print with tweezers, making sure the edges of the print are not
altered.
Photographing prints:
i)
ii)
Place a ruler next to the print for reference and photograph.
Record the film exposure number, species name, collection date,
location, identification number and collector’s name in a notebook.
i)
Place a glass plate over the print, ensuring the plate is flat, which
can be done using adjustable screws as legs in the four corners of
the plate.
Trace the print outline, paying particular attention to its definition.
Record the species name, collection date, location, identification
number and collector’s name, either on the corner of the plate or in
a notebook if the print is then to be traced onto paper.
Tracing prints:
ii)
iii)
Casting Prints (in addition to photographs):
i)
Using the straw, blow talcum powder over the print to prevent soil
particles from sticking to the cast.
ii) Place a casting frame around the print (e.g. paper, cardboard, stiff
plastic).
iii) Prepare the plaster of Paris – add water to the powder stirring continuously until the mixture has a pancake batter texture.
iv) Slowly pour the mixture into the mould evenly, gently tapping to
remove any air bubbles, which may distort the impression.
v) Engrave an identification number onto the cast before it solidifies.
vi) Record the species name, collection date, location, identification
number and collector’s name in a notebook.
vii) Leave casts to harden for approximately two hours (cover with
plastic if rain is imminent).
viii) Remove casting frame and trim excessive edges, leaving a 10mm
border around the print.
89
ix)
x)
xi)
Brush any loose debris from cast.
Package in tissue or bubble wrap.
Store in a cool dry room.
Data analysis
For most species, analysis will be limited to presence/absence, or the
number of track sets and other signs recorded for each species per kilometre
walked. For large carnivores it may be possible to carry out multivariate analyses to identify individuals (e.g. Smallwood & Fitzhugh, 1993) if there are many
measurements.
C. Photo-recording
Photo-recording is expensive and requires patience to overcome malfunctions of cameras, but it can be invaluable in recording the presence of
hard-to-detect species. Setting cameras with automatic trigger mechanisms
allows low-labour monitoring of natural attractions (e.g. salt licks), baited sites
or commonly used thoroughfares. Camera-trapping can also be used to determine activity patterns (nocturnal, diurnal, crepuscular), reactions to disturbance
(e.g. Griffiths & van Schaik, 1993), seasonal movements and breeding patterns, and social structure. If enough cameras are used, it can also provide
some information on abundance. Seydack (1984) gives a good example in
South African forest, and Griffiths (1994) documents successful use in rainforest
conditions for carnivores in south-east Asia. A full discussion of camera-trapping is beyond the scope of this manual. Interested readers should refer to
Karanth & Nichols (1998) and Carbone et al. (2001).
Equipment
●
●
●
Photographic data-recording units, comprising: a) a camera with autowinder (or Polaroid camera), enclosed in weather-proof casing, and
mounted on a stand; b) a flash system with casing; c) a trigger device
such as a trip-plate (300mm x 400mm), trip/bait wires, or a movement
or heat sensor; and d) wires/other connectors between trigger and
camera.
Passive cameras have either a trip-plate or a movement/heat sensor.
A problem with movement sensors is that most types are triggered too
easily (for example, by falling leaves or fruit). However, a laser sensor
is available that can be set to send a beam at different pulses, and
when the beam is broken for a certain length of time it activates the
camera; thus, the pulse rate can be set for a specific species.
If a trip-plate is used, it is placed in a narrow place along a path. When
an animal stands on it an electrical connection is made, causing the
90
●
camera to expose a frame when the flash goes off, and the whole system automatically reloads for the next passing animal.
If bait is being used to attract carnivores, then a mechanical trigger
attached to the bait will set off the film and flash when tugged.
Site selection
The camera needs to be facing a path, track or road along which mammals commonly walk. A suitable position can be determined by finding animal
trails crossing paths and by the presence of dung, scrapes and tracks. It is also
important to find places where the track is narrow, and animals pass near the
camera. A set of camera lines can be established to cover the whole survey
area, or in the centre of several sampling units (e.g. Seydack, 1984). A suitable
alternative is to use a baiting station and set the camera so that it will record
any animals that come to the station. This would be preferable in cases where
trails get too much human activity, or to sample small carnivores and other animals that do not habitually travel along roads/trails.
Procedure and Recording
i) Each camera is positioned at a strategic point and can be systematically rotated to maximise the area sampled. If a single camera is used, it can
be moved to different sites at intervals of a few days. Also record weather.
ii) Some trials are necessary to get the best pictures. Film speed, shutter
speed, aperture, distance from the plate, etc. all need to be adjusted to suit
local conditions (e.g. Seydack, 1984).
iii) The majority of camera traps automatically record time and date upon
activation. If not, a board giving the camera number, location and date can be
placed within the field of the photograph, but without interfering with the subjects.
Data analysis
i) The photographs are developed and the species identified, along with
age and sex where possible. For rare species this gives good information on
presence, and sometimes information on population structure. However, be
prepared that the majority of photos will be of empty trails or individuals of a
large group of a single species, such as mangabeys. A lot of film will be
required to obtain a few photos of rare species.
ii) For species where individuals can be distinguished by markings (such
as coat patterns), photos from camera lines or cameras placed in sampling
blocks can be used to count individuals, describe ranging patterns, and
calculate population densities. Plotting the number of new individuals caught on
film against the cumulative photographic effort will give an indication of when
91
the majority of individuals have been photographed in the sample area, and will
enable you to use mark-recapture analysis techniques to estimate densities.
5.4
Conclusions
All observations of animals or their signs should be recorded to build up
a broad picture of their distribution and abundance. For most species this is all
that rapid surveys can accomplish, especially where relatively few animals or
their signs are encountered. However, relative abundance can be determined
more accurately for elephants (with dung transect surveys) and duikers (with a
mixture of day and night transects and net drives). Long-term studies are
essential for reliable population density estimates.
5.5
References
Archer, A.L. (1994). A survey of hunting techniques and the results thereof on two species of duiker
and the suni on Zanzibar Island. Unpublished report to Zanzibar Forestry Development Project.
Barnes, R.F.W. (1988). A Short-cut Method for Obtaining Preliminary Estimates of Elephant
Abundance in Forests. IUCN/WCMC, Cambridge, UK. 9pp.
Barnes, R.F.W. (2001). How reliable are dung counts for estimating elephant numbers? Afr. J. Ecol.
39: 1–9.
Barnes, R.F.W. & Jensen, K.L. (1987). How to Count Elephants in Forests. IUCN African Elephant
and Rhino Specialist Group Technical Bulletin 1: 1–6. IUCN, Gland, Switzerland.
Barnes, R.F.W., Asamoah-Boateng, B., Naada Majam, J. & Agyei-Ohemeng, J. (1997). Rainfall and
the population dynamics of elephant dung-piles in the forests of southern Ghana. Afr. J. Ecol. 35:
39–52.
Bell, R.H.V. (1984). The man–animal interface: an assessment of crop damage and wildlife control.
In: Conservation and Wildlife Management in Africa, pp. 387–416. (Eds. R.H.V. Bell & E. McShaneCaluzi. US Peace Corps Training and Program Support.
Blum, L.G. & Escherich, P.C. (Eds.) (1979). Bobcat Research Conference Proceedings. National
Wildlife Federation Technical Report Series 6.
Bowland, A.E. (1990). The response of red duikers Cephalophus natalensis to drive counts.
Koedoe 33(1): 47–53.
Buckland, S.T., Anderson, D.R., Burnham, K.P. & Laake, J.L. (1993). Distance Sampling:
Estimating Abundance of Biological Populations. Chapman & Hall, London, UK.
Carbone, C., Christie, S., Conforti, K., Coulson, T., Franklin, N., Ginsberg, J.R., Griffiths, M.,
Holden, J., Kawanishi, K., Kinnaird, M., Laidlaw, R., Lynam, A., Macdonald, D.W., Martyr, D.,
McDougal, C., Nath, L., O’Brien, T., Seidensticker, J., Smith, D.J.L., Sunquist, M., Tilson, R. & Wan
Shahruddin, W.N. (2001). The use of photographic rates to estimate densities of tigers and other
cryptic mammals. Anim. Cons. 4: 75–79.
92
Dorst, J. & Dandelot, P. (1983). A Field Guide to the Larger Mammals of Africa. Collins, London,
UK.
Dubost, G. (1984). Comparison of diets of frugivorous ruminants of Gabon. J. Mammol. 65(2):
298–316.
Estes, R.D. (1991). The Behavior Guide to African Mammals: including Hoofed Mammals,
Carnivores, Primates. University of California Press, Berkeley and Los Angeles, California, USA.
Feer, F. (1989). Comparaison des régimes alimentaires de Cephalophus callipygus et C.dorsalis,
bovidés sympatriques de la forêt sempervirente africaine. Mammalia 53(4): 563–604.
Griffiths, M. (1994). Population density of Sumatran tigers in Gunung Leuser National Park. In:
Sumatran Tiger population and Habitat Viability Analysis Report. (Eds. R. Tilson, K. Soemarna, W.
Ramono, S. Lusli, K. Traylor-Holzer & U. Seal). Indonesian Directorate of Forest Protection and
Nature Conservation and IUCN/SSC Conservation Breeding Specialist Group. Apple Valley,
Minnesota, USA.
Griffiths, M. & van Schaik, C.P. (1993). The impact of human traffic on the abundance and activity
periods of Sumatran rain forest wildlife. Conserv. Biol. 7: 623–626.
Haltenorth, T. & Diller, H. (1984). A Field Guide to the Mammals of Africa, Including Madagascar.
Collins, London, UK.
Hill, C.M. (1998). Conflicting attitudes towards elephants around the Budongo Forest Reserve,
Uganda. Environm. Conserv. 25: 244–250.
Hill, C.M. (2000). Conflict of interest between people and baboons: crop raiding in Uganda. Int. J.
Primatol. 21(2): 299–315.
Karanth, K.U. & Nichols, J.D. (1998). Estimation of tiger densities in India using photographic captures and recaptures. Ecology 79: 2852–2862.
Kingdon, J. (1997). The Kingdon Field Guide to African Mammals. Academic Press, London, UK.
Koster, S.H. & Hart, J.A. (1988). Methods of estimating ungulate populations in tropical forests. Afr.
J. Ecol. 26: 117–126.
Lahm, S.A., Barnes, R.F.W., Beardsley, K. & Cervinka, P. (1998). A method for censusing the
greater white-nosed monkey in north-eastern Gabon using the population density gradient in relation to roads. J. Trop. Ecol. 14: 629–643.
Liebenberg, L. (2000). Photographic Guide to Tracks and Tracking in Southern Africa. New
Holland, South Africa.
Muchaal, P.K & Ngandjui, G. (1999). Impact of village hunting on wildlife populations in the western
Dja Reserve, Cameroon. Conserv. Biol. 13: 385–396.
Naughton, L., Rose, R. & Treves, A. (1999). The social dimensions of human–elephant conflict in
Africa: A literature review and case studies from Uganda and Cameroon. Report to IUCN African
Elephant Specialist Group, Human Elephant Task Force. Gland, Switzerland.
Nchanji, A.C. & Plumptre, A.J. (2001). Seasonality in elephant dung decay and implications for censusing and population monitoring in south-western Cameroon. Afr. J. Ecol. 39: 24–32.
Newing, H.S. (1990). Distinguishing antelope dung and tracks - a zoo study of Upper Guinean forest species, West Africa. Unpublished report.
93
Newing, H.S. (1994). Behavioural ecology of duikers (Cephalophus spp.) in forest and secondary
growth, Taï, Côte d’Ivoire. PhD Thesis, University of Stirling, Scotland.
Noss, A.J. (1999). Censusing rainforest game species with communal net hunts. Afr. J. Ecol. 37(1):
1–11.
Nummelin, M. (1990). Relative habitat use of duikers, bush pigs, and elephants in virgin and selectively logged areas of the Kibale Forest, Uganda. Trop. Zool. 3: 111–120.
Panwar, H.S. (1979). A note on tiger census technique based on pugmark tracings. Tigerpaper 6:
16–18.
Peres, C. (1999). General guidelines for standardising line transect surveys of tropical forest primates. Neotropical Primates 7(1): 11–16.
Plumptre, A.J. (2000). Monitoring mammal populations with line transect techniques in African
forests. J. Appl. Ecol. 37: 356–368.
Plumptre, A.J. & Harris, S. (1995). Estimating the biomass of large mammalian herbivores in a
tropical montane forest: a method of faecal counting that avoids assuming a steady state system.
J. Appl. Ecol. 32: 111–120.
Rosevear, D.R. (1974). The Carnivores of West Africa. Trustees of the British Museum (Nat. Hist.),
London, UK.
Seydack, A.H.W. (1984). Application of a photo-recording device in the census of larger rain-forest
mammals. S. Afr. J. Wildl. Res. 14: 10–14.
Smallwood, K.S. & Fitzhugh, E.L. (1993). A rigorous technique for identifying individual mountain
lions Felis concolor by their tracks. Biol. Cons. 65(1): 51–59.
Stander, P.E. (1998). Spoor counts as indices of large carnivore populations: the relationship
between spoor frequency, sampling effort and true density. J. Appl. Ecol. 35: 378–385.
Stuart, C. & Stuart, T. (1995). Southern, Central and East African Mammals. Struik Publishers,
Cape Town, South Africa.
Stuart, C. & Stuart, T. (1997). Field Guide to the Larger Mammals of Africa. Struik Publishers, Cape
Town, South Africa.
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Southern Africa. Struik, Cape Town, South Africa.
Walsh, P.D. & White, L.J.T. (1999). What it will take to monitor forest elephant populations.
Conserv. Biol. 13(5): 1194–1202.
White, L.J.T. (1995). Factors affecting the duration of elephant dung piles in rain forest in the Lope
Reserve, Gabon. Afr. J. Ecol. 33: 142–150.
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94
Observation point:
Address:
Longitude:
Date:
(dd/mm/yy)
Vegetation:
Altitude:
Time at end of watch:
Additional observations (behaviour, food eaten etc.)
Time at start of watch:
No. of animals
UTM (if available):
Form 5.1: Recording Sheet for Sightings from Observation Points
Species
Surveyor:
(total observers)
Survey site:
Latitude:
Weather:
Other:
Start time
of obs.
Male/ Sub
Juv/
Female adults inf
Field sheet ref:
End time of
observation
95
96
Distance
along
transect
Vegetation
Species
Longitude:
Juv/
inf
Cue
Field sheet ref:
Additional observations
Altitude:
Date:
(dd/mm/yy)
Group
spread
End time:
Weather:
Perpendicular
distance
UTM (if available):
No. of animals
Male/ SubFemale adult
Start time:
Vegetation:
Address:
Cue – H (heard) or S (seen)
Perpendicular distance = distance from nearest point on transect to position at which animal was first detected (in metres)
Group spread = spread of group of animals of a single species, recorded in a single sighting (in metres) Observations = behaviour, association with other
species; any other comments
Time
Other:
Transect length:
Latitude:
Survey site:
Surveyor:
(total observers)
Form 5.2: Recording Sheet for Sighting Transects
T/D
Weather:
End time:
Date:
(dd/mm/yy)
Altitude:
Field sheet ref:
Vegetation type and general observations (including description and max. width and length (mm) for tracks)
UTM (if available):
Distance from
transect (cm)
Vegetation:
Start time:
Bolus. state
& diam.
Longitude:
Address:
Form 5.3: Recording Sheet for Dung Transects
Surveyor:
(total observers)
Survey site:
Latitude:
Transect length:
Other:
Distance Species
(km)
Notes: Distance from start = from start of transect; T/D = tracks/dung; Bolus state: A – fresh, whole, moist and smelly; B = fresh, whole and odourless; C1 = > 50% boli intact;
C2 = < 50% boli intact; D = formless, flat mass; E = Decayed to a stage that it cannot be detected at a range of two metres, and would not be seen on a transect unless underfoot (adapted from Barnes & Jensen, 1987) Make measurements of the diameter of intact elephant boli (in cm)
97
Form 5.4: Recording Sheet for Tracks
Surveyor:
(total observers):
Date:
(dd/mm/yy)
Field sheet ref:
Address:
Survey site:
Vegetation:
Weather:
Latitude:
Longitude:
Altitude:
Transect length:
Start time:
End time:
Other:
Location Species
(transect
marker
number)
Soil
type
Soil Vegetamois- tion type
ture
Clarity of
print
Measurements
(mm)
Soil type: S = mostly sandy; C = mostly clay; St = stones; Si = mostly silt.
Use combinations where necessary, e.g. C+St = mostly clay + stones
Soil moisture: dry; damp; wet
Clarity of print: distinct = well-defined with clear edges; fair = mostly well-defined but some
edges ‘spread’ or confused by other tracks or debris; indistinct = clear enough for identification but measurement difficult because of spread, other tracks or debris.
98
6.
Primates
Glyn Davies
6.1
Biology
mona monkey (Cercopithecus mona)
African primates are divided into three taxonomic groups (Oates, 1996):
the small, nocturnal prosimians (20+ species); the monkeys (45+ species); and
the apes (3+
species). Like
humans, nonhuman primates
that are active in
the daytime generally have a poor
sense of smell,
moderate hearing
and excellent eyesight (nocturnal
species are obviously very different,
having weak distance-vision and
acute hearing).
Savannah species
(e.g. baboons) and
the lemurs of
Madagascar are not
discussed in this
chapter, but the forest survey procedures still apply to
these species
where they do
occur in forests.
Prosimians
These primitive primates are separated into two families: the galagos
(Galagonidae) and the lorisids (Loridae). All species are primarily nocturnal
(Charles-Dominique, 1977). Forest galagos are generally small (18+ species;
50–300g), although three species exceed 1,500g in weight. They live in small
family units, travelling and foraging in the understorey and middle canopy of
99
the forest, and make distinctive calls between group members to maintain contact. Loud calls are made when alarmed, and to signal to other groups/individuals. Recent taxonomic work has shown how these calls are important in distinguishing different species (Bearder et al., 1995).
The potto (genus Perodicticus) and two angwantibo species (genus
Arctocebus) are larger (400g–1,500g), mostly solitary, and move slowly along
branches or through liana tangles, often in the middle and upper canopies of
the forest. Angwantibos will also use shrubby undergrowth in clearings. When
not in direct contact, they communicate by scent-marking twigs and branches,
and do not make loud calls.
Guenons
Forest guenons (genera Cercopithecus, Miopithecus and Allenopithecus)
are relatively small-bodied monkeys (1–8+kg), which live in groups of about
10–30 individuals occupying stable home ranges that generally cover
20–100ha (Gautier-Hion et al., 1988). All species can be distinguished on the
basis of their species-specific facial colour patterns, and the loud calls given by
the adult males. Calls are made at various times during the day, especially
early morning and late afternoon, and when one group calls this often sets off a
sequence of calls and replies between neighbouring groups.
Many guenons have species’ ranges with a wide altitudinal distribution
and habitat use. Exceptions to this generalisation are: the l’Hoest/Preuss
species group, most of which do not occur in the lowlands (excluding the suntailed monkey, C. solatus, in the lowlands of Gabon), and species which concentrate in riverine/swamp forest environments (e.g. Allen’s swamp monkey,
talapoins), or in forest-edge vegetation (e.g. Sykes monkeys).
Most breeding groups have a single adult male, several adult females
and young. Young adult males tend to leave the group of their birth and travel
substantial distances, sometimes in the company of other adult males,
sometimes as lone males.
Colobus monkeys
There are three taxonomic groups of colobus monkeys: olive (one
species), red (14+ species/subspecies) and black-and-white (five species)
(Davies & Oates, 1997).
The black-and-white colobus species (9.5–13kg) generally live in small
groups (c. 5–15) and occupy small home ranges (20–50ha). Each group has
one, or sometimes two, adult males that engage in daily choruses of territorial
loud calls, often pre-dawn and in the early morning. Despite this noisy behaviour, however, they tend to remain silent and hide when alarmed by humans.
Two exceptions to this ecological model are Angolan pied colobus (Colobus
100
angolensis) in Ituri (Zaire) and Nyungwe (Rwanda) and Black colobus (C.
satanus) in Forêt des Abeilles (Gabon), which live in much larger groups
(sometimes hundreds of animals) in larger home ranges (not territories).
Red colobus (8.5–10kg) adult males lack loud calls, but can be detected
from their occasional noisy chatter and alarm calls on seeing humans. Red
colobus (Procolobus spp) live in groups of 10–50 individuals (sometimes even
larger) occupying home ranges of 50–100ha that are not defended as territories; there is considerable overlap between neighbouring groups. The diminutive olive colobus monkeys, Procolobus verus, (4kg) are very secretive, live in
small groups with one or sometimes two adult males, have a quiet, shrill call,
and often travel in the company of other monkey groups. They are difficult to
detect.
Mangabeys, mandrills and drills
The mangabeys (females: 6kg; males: 10kg), and drills/mandrills
(10–20kg) are large-bodied and live in large groups (drills up to 100;
mangabeys: 15–30+) that travel rapidly over wide areas of forest, often splitting
into smaller groups when foraging. Groups contain several adult males that
make loud calls which may be audible from distances greater than 1km, as well
as the noisy squabbles within groups which indicate a group’s presence within
100m or so. In rare instances, mandrills, Mandrillus sphinx, have been recorded forming hordes of over 500 animals, reflecting a dynamic social system that
can be maintained in large tracts of forest. Most time is spent travelling and
foraging on the forest floor, often noisily searching leaf-litter for insects and fallen fruits, but they also feed and sleep in large trees. Grey-cheeked
mangabeys, Lophocebus albigena, are exceptional in being largely arboreal
throughout the day.
Apes
There are four ape species: chimpanzee, Pan troglodytes, (30–40kg),
gracile (or bonobo or pygmy) chimpanzee, Pan paniscus (25–35kg), and two
species of gorilla (90–200kg), the western lowland gorilla, Gorilla gorilla, and
the mountain gorilla, G. beringei; all are large-bodied and travel long distances
along the ground (McGrew et al., 1998).
Chimpanzees live in fission-fusion communities, so group sizes vary
from small units comprising a mother and offspring to large congregations in
excess of 20 individuals around large food sources (e.g. fruiting fig trees). They
are very vocal, making noisy displays with hoots, shouts and drumming on tree
buttresses, all of which aid detection during surveys. Bonobos have a society
that is more cohesive and influenced by strong female-female bonds. They are
restricted to low-lying forest formations in the Congo Basin south of the Congo
101
River. Gorillas live in stable family groups of 5–30 animals, with a single, or
sometimes two fully adult males. They are less noisy than chimps, but males
do have clearly audible chest-beating displays.
All four ape species leave hindfoot and front knuckle prints when they
travel over damp/soft ground, make nests to sleep in each night (chimps and
bonobos in trees but sometimes on the ground, gorillas in the understorey and
middlestorey and on the ground), and produce large, long-lasting characteristically shaped faeces at sleeping and feeding sites. These signs are commonly
used during surveys, supplemented with evidence from areas damaged during
feeding and play, and records of sightings, loud calls, tree drumming, and
chest-beating.
6.2
Management issues
Primates are important components of forest ecosystems: gorillas can
have a major impact on plant regeneration; guenons pollinate flowers and disperse seeds; colobus monkeys commonly destroy seeds; and the combined
numbers of all primates account for the bulk of medium-sized mammalian biomass in many forests. Their unseen and often unrecorded influence on ecosystem function is an important consideration for forest managers. Moreover, the
loss of forest habitat is a key reason for primate species extinctions (e.g.
Cowlishaw, 1999; Oates et al., 2000).
Probably the most important use of forest primates is exploitative: hunting and trapping for food – or bushmeat. Bushmeat is important in rural communities both in terms of subsistence consumption, providing much needed
animal protein, and for trading activities. In West and Central Africa, where economic hardship has resulted in greater dependence on forest products, there
has been a marked increase in commercial exploitation of primates in recent
years. Large tracts of forest have been heavily hunted to supply primates, and
other species, to ever demanding urban centres. Hunting and trapping of primates is less common in the drier southern and eastern African regions where
cattle do relatively well and consumption of primate meat is often disdained on
religious or cultural grounds; however, it does still occur.
Larger species tend to be the main target of the bushmeat trade,
because these animals supply more food for each cartridge spent, and traditional taboos on hunting apes are increasingly being ignored, with the result
that these large-bodied animals are now used in trade. Smaller species are
taken when encountered, and when larger species have been eliminated. In
addition to hunting for food, some primates are consumed for other reasons
that can have significant localised impacts. These include: providing ceremonial
skins (e.g. black-and-white colobus); selling trinkets for the tourist trade (e.g.
102
gorilla hands); supplying animals for the pet trade; supplying biomedical
research centres (e.g. chimpanzees). All these activities obviously lead to
declines in the target species.
The size of forest primates is a less useful factor for predicting timber
extraction impacts. For all forest species, there is a risk that as forest habitat is
altered it will become less suitable, thereby eliminating the least adaptable
species first. Gathering of forest products has long affected forests throughout
Africa, and primates have continued to survive, but the scale and rate of recent
commercial timber extraction has radically altered forest quality. A recent
review of the effects of logging on primates (Plumptre & Johns, 2001) indicates
that very few African primates are actually lost as a result of habitat changes
following logging, with red colobus at some sites being an exception (e.g.
Skorupa, 1986). However, long-term effects of vegetation changes are hard to
predict (e.g. Chapman et al., 2000), and improved access for hunters and trappers along logging roads is a major secondary impact of logging.
A common problem that arises at the forest-farm boundary is that of crop
raiding by primates which refuge in the forest; this is a major management
issue. Guenons and mangabeys are common pests of cash and food crops,
and even galagos are considered as pests of cashew nuts on the Kenya coast.
Chimpanzees and gorillas are keen on bananas and plantains and can do substantial damage in a short time to these flimsy plants. The consequence is that
farmers kill the primates in order to protect their crops, which has resulted in
losses of even protected species such as gorillas on the periphery of the
Bwindi Impenetrable National Park in Uganda.
A positive attribute of primates is that tourists find them attractive and
interesting. In areas with a large number of primate species, ideally at high
population densities, there is ample scope for ecotourism development, even
where thick forest vegetation hampers viewing. In Uganda, this has been
developed for the two largest, and most tourist-attractive, species: the chimpanzee and the gorilla. In all cases, the animals have been habituated to
human visits, and this usually takes a long time. There is an associated risk
that animals that lose their wariness of humans become easy targets for
hunters, or become pests around farms, villages and tourist hotels. They also
become vulnerable to contracting human diseases from visiting tourists
(Butynski & Kalina, 1998).
Ecotourism and the maintenance of primate populations are obvious
complementary activities. In this context, the IUCN conservation action plan for
African primates (Oates, 1996) makes the point that dry forest and savannah
zone primates in Africa have wide distributions and occur in many protected
areas, whereas the populations of the majority of primates from the six lowland
forest and four upland/highland forest communities are under much greater
103
threat. Surveys of the distribution and abundance of primates are therefore
needed to guide conservation planning and action, as well as obtain facts to
inform forest management.
6.3
Methods
General
Survey methods for primates have been thoroughly reviewed in a 1981
publication by a subcommittee of the US National Research Council (NRC,
1981) on the Conservation of Natural Populations, to which reference should
be made. The interpretation of survey field data relies on an understanding of
primates’ reproductive biology, ecology and behaviour, which has been collected from long-term studies of primates. Examples of long-term study sites in
Africa include: Kibale and Budongo in Uganda; Tana River and Kakamega in
Kenya; Gombe and Mahale Mountains in Tanzania; Virunga Volcanoes in
Rwanda; Tiwai Island in Sierra Leone; Taï in Côte d’Ivoire; and Makokou and
Lopé in Gabon. Information from these and other sites should be consulted
before embarking on a survey.
Selecting a survey method involves a compromise between time/personnel available and the information needed for management planning. It is therefore important to write down clearly what questions the survey is to answer,
and then decide if there are sufficient resources to gather this information.
Before making a final decision on which methods to choose, a quick walk
through an area is important to make a general assessment of the populations
to be surveyed, and identify future transect survey sites.
Identification
The use of field guides, such as those discussed in section 5.3 for large
mammals, should be supplemented with information on the colour of animals,
based on examination of skin collections in museums, on live specimens in
zoos, and on an appreciation of the vocal repertoire of different species. There
are few primate call sound libraries, so it is helpful to visit an existing study
area where primate calls can be learned. Such visits also provide an opportunity to make inquiries about local names and develop a general understanding
about species’ ecology, abundance and interaction with human populations.
The survey team’s ability to identify primate species correctly is central to
obtaining useful results; time spent in training will pay good dividends during
surveys.
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6.3.1
Distribution surveys
One of the first things that should be determined is what primate species
occur in the area. This can be done by checking a range of sources, including
records from the literature and museum specimens, and by spending time with
local farmers and hunters, as well as with forest, wildlife, national parks and
other government officers. The interview information needs to be verified carefully (see section 2.6), and then recorded onto standard checklists (Form 6.1),
which can then be computerised and marked onto maps.
The information on distribution maps, which show where different
species occur, or have occurred in the past, can be presented on a range of
scales from local to global. To facilitate transposing information from one scale
to the next, it is important to use a standard mapping unit from the outset, such
as degrees (or quarter degrees) of latitude and longitude or the UTM global
metric grid. This allows countrywide maps to be drawn, onto which changes in
species distribution can be mapped over time (see Fig. 6.1).
At the local level, an accurate (1: 50 000 scale) topographical map is
needed, supported with recent aerial or satellite photographs if available.
These should be used to assess information on vegetation and altitude, and
proximity of villages, roads, urban centres, etc. Thereafter, visits can be made
to different areas, and by mapping all reliable sightings and other records a
preliminary assessment can be made of which areas are suitable for primates.
This information is very important to guide forest management, but it is insufficient to estimate population densities.
Fig. 6.1: Distribution of four primate species in Sierra Leone
(Grubb et al., 1998)
105
6.3.2
Line transects
Line transect methods for surveying vertebrate populations (review in
Buckland et al., 1993) have been adapted for forest primate surveys (see
reviews: NRC, 1981; Whitesides et al., 1988; Peres, 1999; Plumptre, 2000).
The main aim of these surveys is to determine the population density of primates in the area and to ascertain what factors play a role in affecting their
numbers.
Equipment/personnel
The details of general survey equipment, personnel and site selection
have been elaborated in the previous chapter (section 5.3.3). The same principles should be applied for primates, although direct surveys of mobile, groupdwelling species present their own problems that will be discussed in the section on data analysis.
Site selection
i) On an accurate map, select the places where transects should begin,
and the direction in which they should run. This can be done using random
number tables to select transect start points and bearings. Alternatively, transects can be laid out to sample particular areas of interest on a stratified sampling basis depending on the area and spread of forest habitats. Transects can
be cut to point in different directions and should be at least 1km apart at all
points, to gain an idea of population densities over a wide (and therefore representative) area (see section 5.3.3. for further discussion). Straight line transects
should be cut through the forest, following a compass bearing.
ii) Local hunters and guides can help in locating suitable campsites and
transect start points. As noted for ungulates, transects should not begin too
close to the camp noises and smells (over 300m away).
iii) The use of established roads, tracks and paths greatly reduces the
time spent in establishing a survey transect. However, this tends to introduce
serious bias to the survey, because: a) the roadside vegetation differs significantly from the rest of the forest, and/or b) primates change their behaviour in
relation to the road, track or path (e.g. if hunters commonly use them).
iv)Once the transects have been cut, ensure that the survey area has a
distinctive name, and that each transect is clearly distinguished from the others
by a unique number. After cutting the transect, wait at least 24 hours before
proceeding with the survey so that primates can recover from the disturbance
to the area.
106
A. Animal sightings
Procedure
i) Early in the morning (soon after dawn) or in the afternoon (after about
15:00), a surveyor (or small group of surveyors) should walk slowly and quietly
along the transect. For example, Butynski (1984) walked at less than 1km/hr,
stopping every 60m for 30–60 seconds to look around and listen, and others
(e.g. Peres, 1999) have described similar speeds of 1.25km/hr.
ii) Transects should not be crossed by other survey teams during the
survey period, since this will disturb groups which may leave the area to be
surveyed.
iii) The ability to detect primates may be affected by the weather: some
species call less on windy days and all are more difficult to see in windy and
rainy conditions. As a result, it is important to avoid surveys during rain, and
immediately afterwards, when the sound of dripping water obscures other
sounds.
iv)Other factors affecting survey results include: a) time of day –
primates tend to be more active in the early morning and late afternoon;
b) human activities – primates call less and are more wary in areas where
there is hunting; and c) the experience of the observer. These parameters all
need to be recorded (see top section of Form 6.1).
Recording
i) At the first encounter with a primate, the means of ‘detection’ (sighting,
branch movement, falling fruit, alarm calls, fleeing animals, etc.) should be
noted immediately, and the recording sheet filled out as fully as possible (Form
6.1). It is very important to make accurate measurements of the distance from
the transect to all individuals that are seen (see Fig. 6.2). The perpendicular
distance from the transect to each primate should be determined by direct
measurement, using a tape measure, marked (non-stretch ropes), or optical (or
laser) range-finder. As mentioned in section 2.5, estimating distance by eye is
fraught with inaccuracy and variability between observers, and, over time, the
calculation of perpendicular distance from the observer to animal and the angle
of sighting introduces two potential sources of error.
ii) It is often useful to put a field bag on the transect at the point from
which the first animal was seen, as a reference point from which other measurements can be made. The places where animals were first seen need to be
clearly recognised, and the transect marker nearest the observer should be
recorded.
107
Fig. 6.2: Line transect
iii) Information should be gathered about the primate group itself,
including: how many different individuals were seen (adult males, females,
monkey
infants, any special marks like bent
group
tails, etc.); estimated group size
(including those heard but not seen);
perpendicular
the area over which sighted animals
distance
are spread, as well as the overall
group spread. Time should be allowed
observer/animal
to move up and down the transect,
distance
and left and right, to gather this information, although it is important not to
sighting
move away from the transect for more
angle
than 10 minutes.
iv) Other behavioural details to record include: what the group was doing
when encountered (if feeding, what were the animals feeding on); the group’s
reaction upon seeing the observer (e.g. wary curiosity, panicked flight, indifference, etc.); at what height, and in what type of vegetation, they were found.
Transect
route
Data analysis
To calculate the population density in groups/km2, three sets of data are
required:
i) The length of transect surveyed, which is determined by multiplying the
length of the transect by the number of times it was surveyed.
ii) The number of groups encountered, which should include all those
groups containing both males and females, with a separate note of groups
which appeared to contain only adult males; solitary animals should also be
noted separately.
Using these two pieces of information the relative abundance of a
species (e.g. groups per kilometre walked) can be calculated. This was done in
Kibale, where Skorupa (1986) provided statistically robust data that showed differences in primate numbers between logged and unlogged forests. But this
can only be done if it is possible to determine differences in the probability of
detecting primates at either site (Skorupa, 1987).
iii) The width of the survey strip multiplied by the distance surveyed will
give an area of forest in which a certain number of primate groups were recorded; this, in turn, provides an indication of population density (groups/unit area).
However, the detectability of groups on either side of the transect line is not
fixed, i.e. it is not possible to say that all groups within 40m on either side of the
transect will be seen, and all those more than 40m away will not be seen.
108
The transect width is influenced by: a) the detectability of the species
(e.g. shy versus conspicuous behaviour); b) vegetation type; c) terrain; and d)
the spread of a group (Whitesides et al., 1988). All these parameters can vary
between sites, seasons and species, and to be able to estimate the transect
width it is necessary to gather enough information on species-specific and
habitat-specific observer–animal sighting distances (preferably 40–100 independent field records for each species at each survey site). With these data,
the effective strip width for sighted individuals can be calculated using the
DISTANCE programme (Buckland et al., 1993; see section 5.3.3).
A complicating factor in judging the width of a transect is the group
spread (the area occupied by a group of monkeys). This will influence how
many monkeys you see at a given group encounter, since the presence of one
group affects the locality of other groups, as well as the concentration of monkeys within an area (Fig. 6.3). Some surveyors have tried to address this problem by estimating average group spread for each species (from long-term studies), and adjusting transect width estimates accordingly to the anticipated centre of the group from the transect (Whitesides et al., 1988). However, others
advise against this approach, emphasising that it is necessary to use only
sighting data for all individuals seen (Plumptre, 2000), and calculating the
centre of the group spread from the centre of the sightings.
cumulative number of group sightings (%)
Fig. 6.3
The cumulative number of
sightings of groups of two
species of primates:
spot-nosed monkey [s],
Cercopithecus petaurista,
and Diana monkey [d],
Cercopithecus diana, with
increasing distance on
either side of the transect.
The two triangles show the
distance from the transect
within which 80% of all
group sightings were made
(adapted from Whitesides
et al., 1988).
100
80
60
40
20
s
10
20 30
d
40 50 60 70 80 90 100
perpendicular distance from the transect (m)
109
Advantages/limitations
i) Given the poor visibility in forest conditions, and the short time over
which surveys are conducted, obtaining detailed estimates of population densities is very difficult. However, clear estimates of the relative abundance of primates at different sites is often adequate for management purposes (for example, knowing that there are more primates of species X in forest A than in forest
B). Certainly it can give a clear indication of areas that need special management attention.
ii) The use of DISTANCE software to analyse survey results is based on
a number of basic assumptions (see section 5.3.3). Some of these factors are
outside the control of the observer, but the quality of field records is greatly
improved if time is taken to develop an understanding of the primates being
surveyed, and to do practice surveys (Peres, 1999).
iii) The number of times that surveys must be repeated depends upon
the length of the transect and the number of encounters per kilometre. As a
rough guide, 100 records were determined as a minimum sample size for
robust statistical analysis in Budongo forest (Uganda), which required over 200
km of surveys (Plumptre, 2000). Smaller sample sizes can be used, but statistical confidence limits associated with density estimates need to be shown
clearly.
iv)The line transect survey method can be used by a single observer (or
small survey team), which is a major advantage when manpower constraints
limit survey work. However, the observer needs to be experienced with species
behaviour for this method to be effective.
B. Nest counts
The nests that are made by gorillas and chimpanzees, both for sleeping
at night and also for resting during the day, persist on the ground or in trees
well after they were first made. These conspicuous signs of species’ presence,
which generally occur at low population densities, have long been used in surveys (e.g. Tutin & Fernandez, 1983). The same principles described for indirect surveys of ungulate signs along transects and recce tracks can be applied
(section 5.3.4), and are described in more detail by White & Edwards (2000) –
using Form 6.2.
As with dung surveys, the critical information needed to translate counts
of nests/km surveyed are: the rate at which nests are made/individual (taking
account of age differences), and the rate at which nests disintegrate until they
are hardly discernible any longer (which will vary with season, altitude, species
and so on). At sites where there are many nests, the need to calculate decay
rates can be avoided by doing repeat surveys (e.g. every one to three months)
and marking all nests seen on a map (or with flagging tape) – see
110
section 5.3.4A. It is then possible to record the number of new nests produced
in a given period of time, within a known survey area (km2), and then to convert
a nest density figure into an estimate of individuals/km2 using a calibration for
the number of nests made per day by different types of animals (males,
females, etc).
A number of studies have been carried out to look at these problems in
different African forests, and they should be referred to for more details
(Hashimoto, 1995; Tutin et al., 1995; Plumptre & Reynolds, 1997; Hall et al.,
1998; Blom et al., 2001).
In summary, the analysis of the results depends on the amount of background information available for the survey area during the season when the
surveys were carried out. If there is good evidence that the nests are from a
particular species, then species distribution maps can be drawn up. As information on nest building and decay rates is determined (by site and season), so it
will become possible to give reasonable estimates of gorilla and/or chimpanzee
populations’ decay rates (which are often variable).
C. Mapping calls
Loud calls can be used to detect groups from greater distances than is
possible with sightings. In areas where species are very vocal this provides a
useful survey method, but even quieter chatters and squeals, and movements
in the branches, can be used to detect primates over shorter distances. See
also sections 3.3.10 and 7.3.9.
Equipment/personnel
●
●
●
●
●
map-making equipment: 360o protractor, graph paper, ruler, pencils,
etc.
high-quality portable tape recorder or mini-disc player, microphone
and batteries, blank tapes or mini-discs (to record unidentified and
unusual calls, or to analyse calls and compare calls between areas
and seasons)
recorded tapes/CDs for playback experiments (to get resident groups
to call)
plastic bag or like for protecting equipment against moisture
surveyors with good knowledge of primate calls
Procedure
i) For diurnal species, the surveyor should start early (just before dawn
for many species) and walk slowly (1km/hr) and wait at marked points to listen
for calls. On hearing a call the surveyor should wait for between 15 and 30
minutes until the calling group, and any that are replying, seem to have
111
stopped. For nocturnal species, the start time of the survey should obviously
change: galagos commonly give loud calls around dusk and during the hour or
so before dawn.
ii) The survey should be repeated for a number of days, depending on
the species, site, season and weather conditions. For vocal species (e.g. blackand-white colobus), as little as three days may be sufficient to record all calling
groups in the survey area, but longer survey periods will be needed at sites
where fewer or quieter calls are made. In general, surveys need to continue
until the number of groups mapped in a given area becomes consistent.
Recording
On hearing a call, the following information must be collected (using
Form 6.3, or a separate sheet for calls): date, time, weather, etc.; species;
detection (type of call); bearing (of the call from the surveyor); observer–animal
(estimated distance to calling animal); map (the trail marker from where the call
was heard). Whenever the same group calls again, after the surveyor has
moved to a new position, new bearings should be taken again so that the
group’s position can be mapped more accurately through triangulation.
Data analysis
i) An accurate map of the survey area should be drawn (useful scale is
10mm: 100m) onto graph paper, including key topographical features (e.g.
streams, ridge tops, etc). Copies of the master map should then be made for
mapping each species separately (Fig. 6.4).
ii) Date and time are marked on a pencil line showing the bearing of the
call, starting from the observer’s position on the map. The distance from
observer to calling animal is estimated and also marked to scale, and special
attention should be given to triangulating calls of the same group that were
given at different times.
iii) Great care must be taken not to double-count groups, especially for
species which travel rapidly over wide areas in a short time and call from different places (e.g. mangabeys). Information on species’ home-range sizes, homerange overlap, travel and foraging patterns (gathered during long-term studies)
are important in determining how to reduce this type of error.
iv)Supplementary information can be added to the species’ maps,
recording those animals seen, but not recorded calling, to give a fuller picture
of all the groups present.
112
Fig. 6.4: Mapping calls and sightings
5/12
6/12
3/12
3/12
6/12
4/12
3/12
5/12
Map of sightings and calls of
Campbell’s monkey,
Cercopithecus campbelli,
during a four-day survey (3–6
December). Numbers refer to
dates. Groups sighted are
squared, and group calls are
shown by arrows indicating
the direction from the surveyor and the arrow-head indicates the estimated location
of the group.
For species with home ranges
of 20–50ha, surveys by small
teams for 20 days, over 6–12
months, give good spread
indications of group densities.
6/12
Survey trail with 100m markers
Advantages/limitations
Since most primate groups call at some time during the day, and the call
can be heard over distances greater than are detectable by sight, inclusion of
calling records greatly increases the sample size of encounters for a unit survey effort. For example, on three morning surveys by two observers in
Kakamega forest (Kenya), there were 86 encounters with primates (sightings
and calls) of which 63% were calls of animals that were not seen (Davies, pers.
obs.).
This method gives accurate information on the numbers of groups in a
given area for those species that are vocal during the survey period. Quieter
groups, species, and times of the year will all give lower quality results.
113
6.3.3
Sweep surveys
In practice, field workers make the most of all their field records by combining information on sightings and calls. This can be done during transect
walks, but even more information can be gained when the surveys are carried
out along parallel transects on a survey grid by a number of surveyors working
simultaneously. These are called sweep surveys (Whitesides et al., 1998).
Equipment/personnel
●
●
survey grid cut and mapped (see below)
at least three experienced field observers
Procedure
i) A rectangular survey area has to be prepared, with three or more survey transects running parallel to each other, spaced at 100-m intervals, and
extending for at least 1km. They should be linked at either end by perpendicular trails, to get surveyors to the start points quickly and quietly. All paths are
marked at 50-m intervals.
ii) Soon after dawn, the surveyors should assemble at the start of their
survey trails and travel slowly and quietly along the path, beginning at a prearranged time (having synchronised watches beforehand). The surveyors move
forwards in a single front, stopping occasionally to make field records. To keep
the line of surveyors coordinated, several pre-determined restart points should
be marked along the survey routes.
Recording
i) When a primate is sighted, its position and the group-spread are
marked on a scale map (e.g. 10mm: 50m). All primate group sightings and calls
are recorded (as noted in sections 6.3.2 and this section above).
ii) By noting the time of all records (sightings and calls), simultaneous
records of the same group by different observers can be mapped, thereby
avoiding double-counting of the same groups.
Data analysis
i) At the end of the survey, all surveyors reassemble and a map is compiled for each species from all records collected. Once the map has been completed for a number of repeat surveys, separate primate home ranges can be
marked, and the number of groups within the survey area and its vicinity can
be counted.
114
ii) Some groups’ home ranges will fall wholly within the survey grid, but
others will be partly outside. Whitesides et al. (1988) considered groups having
home ranges in excess of 80% inside the survey grid as being within the area
surveyed, groups having 80–30% inside the survey grid as half a group, and
groups with 30% or less of their home ranges inside the grid were regarded as
falling outside the survey area. By adding whole groups and half groups, the
number of groups/km2 can be calculated.
iii) Detailed information on the size of primate groups, and their age/sex
composition, combined with information on the body weights of different types
of animals (eg adult males, juveniles, females, etc.), can then be used to calculate population densities and biomass.
Advantages/limitations
This method provides very reliable and accurate estimates of absolute
group densities, plus solitary individuals, within a known survey area. It can be
verified by repeated sweep surveys over time to take account of seasonal
biases.
If the sample area is representative of the forest as a whole, then the
results from these surveys can be extrapolated to wider areas. The disadvantages of this method include the time taken to build up an accurate picture of
group densities, the large number of surveys required, the need for a team of
three or more experienced surveyors (although a team of just two can allow triangulation on calling groups), and clearing and maintenance of the transect grid.
Rapid sweeps
Using the same principle as the sweep surveys, but in circumstances
where there is only one surveyor, the system can be modified to a rectangular
survey area (1km x 500m, depending on the species being surveyed), in which
all sightings and calls of primates are recorded onto accurate maps. Over time,
a picture of the number of groups in the area builds up, although the possibility
of missing groups in the centre of the survey rectangle are higher than for the
sweeps, and groups on the edge may also be missed.
In Sierra Leone, data on relative primate abundance was gathered by a
single observer using survey rectangles of 1km x 500m (e.g. Davies, 1987).
Rapid sweeps have also been used in the small patches of forest along the
Tana River in Kenya (Butynski & Mwangi, 1994), where pairs of observers
searched in a zigzag fashion through parallel swathes of forest with each survey team’s route separated by about 100–150m. The survey routes were carefully mapped, and plenty of time taken to search for primates. At the end of the
survey, all teams met and discussed results before group encounters were
mapped and the numbers of groups in each patch calculated.
115
6.4
Conclusions
There are a range of primate survey methods that have been adapted
for particular conditions and resource constraints, many of which depend on
combining records of primate calls and sightings. Selection of any one method
should be determined by the question that has to be answered, and care must
be taken to allocate the necessary resources required (e.g. time, personnel,
transport, cash, etc).
Given the problem of resource and personnel constraints, line transects
are a useful and common survey method. They are practical for determining
the relative density of primates at different sites as long as there are sufficient
encounters to determine transect width. Sweep surveys are most useful for
determining primate group density in areas of about 1km2.
Whatever survey method is being used, a rule of thumb is to gather as
much field information as possible, during transect walks, when in the camp,
when meeting with local hunters and villagers, and so on. All of this will help
improve the interpretation of field survey results.
6.5
References
Bearder, S., Honess, P.E. & Ambrose, L. (1995). Species diversity among galagos, with special reference to mate recognition. In: Creatures of the Dark: The Nocturnal Prosimians, pp 331–352.
(Eds. L. Alterman, G.A. Doyle & M.K. Izard). Plenum Press, New York, USA.
Blom, A., Almasi, A. & Heitkonig, I.M.A. (2001). A survey of the apes in the Dzanga-Ndoki National
Park, Central African Republic: a comparison between the census and survey methods of estimating the gorilla (Gorilla gorilla gorilla) and chimpanzee (Pan troglodytes) nest group density. Afr. J.
Ecol. 39(1): 98–105.
Buckland, S.T., Anderson, D.R., Burnham, K.P. & Laake, J.L. (1993). Distance Sampling:
Estimating Abundance of Biological Populations. Chapman & Hall, London, UK.
Butynski, T.M. (1984). Ecological survey of the Impenetrable (Bwindi) Forest, Uganda, and recommendations for its conservation and management. Unpublished report to the Government of
Uganda. pp. 150.
Butynski, T.M. & Kalina, J. (1998). Gorilla tourism: a critical look. In: E.J. Milner-Gulland & R. Mace
(eds), Conservation of Biological Resources, pp 280–300. Blackwell Science, Oxford, UK.
Butynski, T.M. & Mwangi, G. (1994). Conservation status and distribution of the Tana River red
colobus and crested mangabey. Unpublished report to the Kenya Wildlife Service. pp. 67.
Chapman, C.A., Balcomb, S.R., Gillespie, T.R., Skorupa, J.P. & Struhsaker, T.T. (2000). Long-term
effects of logging on African primate communities: a 28-year comparison from Kibale National Park,
Uganda. Conserv. Biol. 14(1): 207–217.
Charles-Dominique, P. (1977). Ecology and Behaviour of Nocturnal Primates: Prosimians of
Equatorial West Africa. Duckworth, London, UK.
Cowlishaw, G. (1999). Predicting the pattern of decline of African primate diversity: an extinction
debt from historical deforestation. Conserv. Biol. 13(5): 1183–1193.
116
Davies, A.G. (1987). The Gola Forest Reserves, Sierra Leone: Wildlife Conservation and Forest
Management. IUCN, Gland, Switzerland.
Davies, A.G. & Oates, J.F. (1997). The Colobine Monkeys: their Ecology, Behaviour and
Conservation. Cambridge University Press, Cambridge, UK.
Gautier-Hion, A., Bourliere, F. & Gautier, J-P. (1988). A Primate Radiation: Evolutionary Biology of
African Guenons. Cambridge University Press, Cambridge, UK.
Grubb, P.A., Jones, T.S., Davies, A.G., Edberg, E., Starin, E.D., Hill, J.E. (1998). Mammals of
Ghana, Sierra Leone and The Gambia. Trendrine Press, UK.
Hall, J.S., White, L.T.J., Inogwabini, B.I., Ilambu, O., Morland, H.S., Williamson, E.A., Saltonstall, K.,
Walsh, P., Sikubabuo, C., Dumbo, B., Kaleme, P.K., Vedder, A. & Freeman, K. (1998). A survey of
Grauer gorillas (Gorilla gorilla graueri) and chimpanzees (Pan troglodytes schweinfurthii) in the Kahuzi
Biega National Park lowland sector and adjacent forest in eastern Congo. Int. J. Primatol. 19: 207–235.
Hashimoto, C. (1995). Population census of the chimpanzees in the Kalinzu Forest, Uganda: comparison between methods with nest counts. Primates 36: 477–488.
McGrew, W.C., Marchant, L.F. & Nishida, T. (1998). Great Ape Societies. Cambridge University
Press, Cambridge, UK.
National Research Council. (1981). Techniques for the Study of Primate Population Ecology.
National Academy Press, Washington D.C., USA.
Oates, J.F. (1996). African Primates: Status Survey and Conservation Action Plan. IUCN, Gland,
Switzerland.
Oates, J.F., Abedi-Lartey, M., McGraw, W.S., Struhsaker, T.T. & Whitesides, G.H. (2000). The possible extinction of a West African Red Colobus monkey. Conserv. Biol. 14(5): 1526–1532.
Peres, C. (1999). General guidelines for standardising line-transect surveys of tropical forest primates. Neotrop. Primates 7(1): 11–16.
Plumptre, A.J. (2000). Monitoring mammal populations with line transect techniques in African
forests. J. Appl. Ecol. 37: 356–368.
Plumptre, A.J. & Reynolds, V. (1997). Nesting behavior of chimpanzees: Implications for censuses.
Int. J. Primatol. 18: 475–485.
Plumptre, A.J. & Johns, A.D. (2001). Primate populations. In: Wildlife-logging Interactions in Tropical
Forests. (Ed. by R.A. Fimbel, A.Grajal, & J. Robinson). Colombia University Press, New York, USA.
Skorupa, J.P. (1986). Responses of rainforest primates to selective logging in Kibale forest,
Uganda: a summary report. In: Primates: the Road to Self-sustaining Populations, pp 57–70. (Ed.
K. Benirschke). Springer-Verlag, New York, USA.
Skorupa, J.P. (1987). Do line-transect surveys systematically underestimate primate densities in
logged forests? Am. J. Primatol. 13: 1–9.
Tutin, C. & Fernandez, M. (1983). Recensement des gorilles et des chimpanzés du Gabon. CIRMF,
Gabon.
Tutin, C.E.G., Parnell, R.J., White, L.J.T. & Fernandez, M. (1995). Nest-building by lowland gorillas
in the Lope-Reserve, Gabon – environmental-influences and implications for censusing. Int. J.
Primatol. 16: 53–76.
White, L. & Edwards, A. (2000). Conservation Research in the African Rain Forests: a Technical
Handbook. Wildlife Conservation Society, New York, USA.
Whitesides, G.H., Oates, J.F., Green, S.M. & Kluberdanz, R.B. (1988). Estimating primate densities
from transects in a West African rain forest: a comparison of techniques. J. Anim. Ecol. 57:
345–367.
117
Form 6.1: Primate Recording Sheet for Line Transects
Surveyor:
(total observers):
Field sheet ref:
Date:
(dd/mm/yy)
Altitude:
Aspect:
Address:
Survey site:
Latitude:
Longitude:
UTM (if available):
Vegetation:
Season:
Transect length:
Human disturbance:
Weather:
Lunar phase:
Start time:
Other:
Time
Species
Detection
Bearing
Transect-Animal
Distances (m)
Transect-Estimated
Group Centre (m)
MAP (m from start)
Estimated & Sighted
Number
Age/Sex
Group Spread
Activity
Reaction
Notes
118
End length:
Temperature:
Nest
Vegetation:
Start time:
Dimensions
Longitude:
Address:
Form 6.2: Recording Sheet for Nest Counts
Surveyor:
(total observers)
Survey site:
Latitude:
Species
Transect length:
Other:
Distance
from start
(km)
Weather:
End time:
Date:
(dd/mm/yy)
Altitude:
Field sheet ref:
Distance
Additional observations
from transect (m)
UTM (if available):
State/age
Notes: Distance from start = from start of transect; species (based on evidence from faeces, hair other evidence); nest – in tree or on ground; woody or herbaceous, etc; dimensions (widest and narrowest diameter in cms); state\age: A = fresh, still with animal odour; B = recent, still with green leaves, but no odour; C = old, intact but no green foliage;
D = very old and disintegrating (after White and Edwards, 2000); distance from transect – perpendicular distance from the transect (m)
119
Form 6.3: Primate recording sheet for mapping calls
Surveyor:
(total observers):
Field sheet ref:
Date:
(dd/mm/yy)
Altitude:
Aspect:
Address:
Survey site:
Latitude:
Longitude:
UTM (if available):
Vegetation:
Season:
Transect length:
Human disturbance:
Weather:
Lunar phase:
Start time:
Other:
Time
Species
Detection
Bearing
Observer–Animal (m)
MAP (m from start)
Age/Sex
Group Spread
Activity
Reaction
Notes
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End length:
Temperature:
7.
Birds
Jameson’s wattle-eye (Platysteria jamesoni)
Leon Bennun and Kim Howell
7.1
Biology
Birds are the best-known group of vertebrates. There have been numerous studies on forest birds of eastern Africa, and most species are readily identifiable using field guides and standard reference works. Birds play an important role in forests as pollinators of flowers and dispersers of seeds. Many of
the smaller species also eat large numbers of insects and other arthropods.
Birds, in turn, are preyed upon by reptiles, mammals, and other birds. The
African crowned eagle, Stephanoaetus coronatus, is an example of a top
predator in some forests, and may take prey as large as colobus monkeys.
Birds are often considered as a useful indicator group, either for monitoring environmental change (see Furness et al., 1993) or for assessing biodiversity importance (Thirgood & Heath, 1994; Stattersfield et al., 1998). Birds as a
group have many characteristics that make them good indicators: they are
well-studied, taxonomically stable, easily surveyed, widely-distributed across
almost all habitats, and include both generalised and specialised species.
There are enough bird species (more than 1,300 in East Africa; more than
2,170 in Africa and Madagascar) to make meaningful comparisons between
sites, but few enough that taxonomic and identification problems are rarely an
issue. However, there are few precise details and guidelines on how birds can
be used as indicators. Bennun & Fanshawe (1998) discuss bird surveys to
121
evaluate the effects of forest management, while Howard et al. (1998) demonstrate that information on birds can be used to select a set of priority sites for
biodiversity conservation, even if the distributions of birds and other animals
and plants are poorly correlated.
Categories of forest-dependence
About one-third of the bird species in East Africa are found in forest.
However, the extent to which they depend on forest differs. Bennun et al.
(1996) list forest birds in Kenya and Uganda, in three categories:
● FF species (forest specialists) are the true forest birds, characteristic
of the interior of little-disturbed forest. They may persist in secondary forest and
forest patches if their particular ecological requirements are met. Where they
do occur away from the interior, they are usually less common. They are rarely
seen in non-forest habitats. Breeding is almost invariably within forest.
● F species (forest generalists) may occur in undisturbed forest but are
also regularly found in forest strips, edges and gaps. They are likely to be more
common there and in secondary forest than in the interior of closed-canopy
forest. Breeding is typically within forest.
● f species are birds which are often recorded in forest, but are not
dependent upon it. They are almost always more common in non-forest
habitats, where they are most likely to breed.
These categories can be applied to forests elsewhere in Africa, although
the same species may fall into different categories in different parts of its range
(Bennun et al., 1996).
The forest-specialist birds tend to have smaller distribution ranges than
the other categories, and are more likely to be threatened with extinction
(Bennun et al., 1996). This is not surprising, because they are less tolerant of
habitat disturbance than other species. The exact ecological requirements of
most forest-specialist species are still poorly known, but many seem to use a
narrow range of habitats within the forest undergrowth or the canopy. Changes
in the forest structure, brought about, for example, by selective logging, may
make it difficult for them to survive and reproduce successfully. Removal of forest causes them to disappear entirely. In most cases, conversion to plantations
will have a similar effect: very few forest birds survive in plantation forest,
except where indigenous tree species are planted.
Some forest birds are long-distance migrants (for example, the African
pitta, Pitta angolensis), while others (such as some parrots, hornbills and barbets) may make long movements in search of patchy supplies of food. Many,
however, spend their whole lives within a small area of forest and may be
reluctant to cross even small gaps between forest patches (Newmark, 1991).
Forest species that migrate altitudinally between montane and lower-altitude
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forests present a particularly complex conservation problem, as forests at both
altitudes must be maintained.
Feeding guilds
If comparisons are to be made across space (i.e. between sites) or time
(i.e. monitoring at a particular site) then it is often useful to be able to subdivide
the data according to forest dependence and guild categories. Guilds are
groups of birds, not necessarily taxonomically related, that feed or behave in a
similar way – for example bark-gleaning insectivores or just insectivores are
both guilds. Bennun & Fanshawe (1998) show that these classifications can be
useful for understanding the effects of forest management, since different
guilds respond differently to particular structural changes. One advantage of
using guilds or forest-dependence categories is that they average out the idiosyncratic responses of individual species, so that a more general pattern
emerges.
Plumptre & Owiunji (unpubl.) have developed the following set of feeding
guilds for Budongo forest in Uganda (with codes for computerising data):
Feeding strategy
Code
Frugivore
Frugivore-insectivore
Insectivore
a. Sallying – from perch to flying insect
b. Ground – feeds on insects in leaf litter
c. Gleaning
c1: Gleans from leaves
c2: Gleans from bark
Gramnivore (seed-eater)
Gramnivore-insectivore
Nectarivore-insectivore
Omnivore
(eats many types of food)
Raptor
a: catches below canopy
b: catches at canopy mainly
FR
FRIN
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INsa
INgr
INglL
INglB
GR
GRIN
NEC
OM
RAPb
RAPc
Feeding height
Different bird species make use of different levels in the forest, so it is
important to record species that are being seen. Three simple categories can
be used:
1. feeds at or within three metres of ground level
2. feeds in the middle strata of the forest
or in understorey tree canopies
3. feeds at forest canopy height (in tallest trees)
GRD
MID
CAN
This classification provides a useful level of detail (Bennun & Fanshawe,
1998) and is recommended for application in other African forests.
If survey data are to be lumped into forest-dependence or guild categories, this may affect the survey methods that are chosen. Not all survey
methods produce data that can be pooled in this way (see section 7.3 below).
7.2
Management issues
Intact natural forest is a diminishing habitat everywhere. This puts forestspecialist bird species at risk. In places where large blocks of forest have
become fragmented, bird populations that were once continuous are now split
into isolated units that may have limited interchange with each other (e.g. Lens
et al., 1999). Fragmentation has other negative effects: fragments have relatively more edge and less interior than large blocks; they are especially vulnerable to habitat degradation; and they may be easier for predators or parasites
to penetrate. Local extinctions have already been demonstrated in small forest
fragments across East Africa (e.g. Tanzania: Newmark (1991); Kenya: Brooks
et al. (1998); and Uganda: Dranzoa (1993)). In the Taita Hills, the asymmetry of
birds’ plumage features (fluctuating asymmetry, a sign of stress) increases in
smaller forest fragments (Lens & van Dongen, 1999), and there may be concomitant effects on population sex-ratios (Lens et al., 1998).
Management strategies to mitigate the effects of fragmentation may
include restoration or maintenance of habitat corridors (e.g. forest strips along
river valleys) and more effective protection from human disturbance. Where
large forest blocks remain, zoning and control of forest exploitation should be
designed to prevent habitat fragmentation occurring in the first place.
Habitat degradation also has negative effects on forest birds. The populations of forest-specialist species decline as the structure of the habitat is
modified (see Bennun & Fanshawe, 1998 for a review). Mechanised logging is
the most conspicuous form of habitat degradation, but severe damage may
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also be done by non-mechanical methods such as pit sawing. On a small
scale, logging opens up gaps that mimic natural tree-falls and increase the
diversity of species – but at the expense of the sensitive forest-interior birds.
Exploitation for poles and fuelwood, and grazing by livestock, can cause
serious problems for forest-specialist species. Collection of fallen deadwood
affects insect populations, and thus birds too. Hole-nesting birds such as woodpeckers, barbets and hornbills rely heavily on standing deadwood or old, overmature trees where nest-sites can be found or excavated (Newton, 1994; Du
Plessis, 1995). A forest that is well managed for timber, with dead or dying
trees carefully removed, may be very badly managed for birds (and other biodiversity).
Tye (1993) reviews many of the relevant conservation issues with examples from Tanzania. Generally, arguments for the sustainability of these forms
of forest use must be critically assessed; in practice, sustainability usually
means a particular trade-off between economic benefits and biodiversity loss.
Deciding whether such a trade-off is acceptable or not requires detailed ecological knowledge about the species of conservation concern and a monitoring
programme to assess the effects of forest-use, both local (e.g. Hall & Rodgers,
1986) and commercial.
Some bird species are hunted for food. In East Africa at least, this is not
usually a concern for most forest species. However, it may be a problem for a
few, such as forest francolins; for example, hunting already poses a threat to
the Udzungwa partridge, Xenoperdix udzungwensis, which has a restricted distribution range in Tanzania. Capture of birds for the live-bird export trade affects
a small number of forest species, such as the grey parrot, Psittacus erithacus.
Any legal offtake of birds, for local use or export, must be controlled properly
and based on detailed distribution and population studies for the species
concerned. Such control measures do not currently exist.
Birds can themselves be used as a management and conservation tool
(Bennun, 1999; Bennun & Njoroge, 1999). At one level, they are likely to be the
easiest group to monitor if changes in forest biodiversity need to be assessed.
At another level, they provide an excellent focus for conservation education
and action. For example, site-support groups with a birdwatching emphasis are
already active around several forest Important Bird Areas in Kenya.
Birdwatching has great tourism potential in East African forests, and can provide a source of local employment and revenue generation. Although birds still
lack the public profile of large mammals, in East Africa they are receiving
increasing attention and increasingly high priority in conservation and management. For example, in Tanzania, the finding of a new species of bird (as well as
of other vertebrates) helped catalyse the establishment of that country’s first
forest National Park.
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7.3
Methods
General
Surveys of forest birds may be undertaken for a variety of reasons,
including:
● characterising the avifauna of a little-explored site;
● comparing the bird communities of different forests, in order to set
conservation priorities;
● tracking changes in bird communities in relation to forest management
(a form of monitoring: see below);
● investigating the distribution and status of particular birds of interest
within a forest, or among a set of fragments.
The different kinds of surveys differ in whether they require simple lists,
measures of relative abundance, or measures of absolute abundance. Simple
lists are the easiest kind of information to collect. However, with very little extra
effort it is possible to collect information on relative abundance. This allows
comparison of sites within and between forests and is generally much more
useful. It is at this level that most survey work is carried out. Assessing the
actual population densities of birds requires considerably more work, and
should only be undertaken if the extra information really justifies the effort.
This chapter provides only a brief outline of the survey methods most
useful for forest birds, many of which have been field-tested in Kenya and
Uganda. For more information and discussion, see Pomeroy (1992) and Bibby
et al. (1998, 2000).
Inventory versus monitoring
Inventory (finding out what species are in a particular site) and monitoring (tracking changes over time) are at opposite ends of a spectrum of survey
types. It is important to be clear about what kind of work you are doing, as
otherwise much valuable effort can be wasted.
Strictly, monitoring implies assessing changes against some target value
or threshold. With forest birds, we are more often involved with surveillance – a
series of surveys over time. In either case, it is important that data are collected in a highly standardised way, on a regular (though not necessarily frequent)
basis. You need to be able to repeat the same kind of data collection at the
same place at the same time. Some useful background and guidelines on surveillance and monitoring can be found in Goldsmith (1991), Stork & Samways
(1995), Tomas Vives (1996) and Bennun (2000, 2001).
The key feature of monitoring (including surveillance) is consistency.
Often, this means that you will only be able to survey a small portion of a
126
particular site. Entire bird communities can be monitored, but monitoring often
concentrates on one or a few key species or species-groups that are particularly significant. For example, depending on your interest or the threats and
changes facing a particular site, monitoring surveys might focus on a threatened species, or a particular feeding guild like large frugivores. Because monitoring aims to detect changes, it is important to minimise the sampling errors in
estimates (see below). This means careful sample design and high-effort, lowcoverage surveys. Suitable techniques for monitoring are those that can be
exactly repeated in the same places time after time, and that give accurate
estimates – for example, fixed- and variable-width transects and point counts.
With inventory, the concern is usually comparisons in space (with other
sites) rather than comparisons over time. The aim is to build up as complete a
picture as possible of a site’s avifauna. Because bird distributions are often
patchy, it is important to cover as much area as possible. Since inventory often
has to be rapid, this means that surveys at a particular location may be relatively superficial. To make sure the species list is complete, different techniques
(such as mist netting, playback and timed species-counts) may need to be
used together, and all available habitats investigated. Absolute abundance
measures are usually unnecessary for inventory work – relative abundance is
enough, so long as similar approaches have been used at the comparison
sites.
Good inventory techniques will thus cover large areas and produce long
species-lists quickly. Examples below include timed species-counts and
MacKinnon lists (and their variants).
Identification
To survey birds you need to be able to identify them, both by sight and
sound. This is not easy in forests. Building identification skills takes time and
effort, although going to the field with more experienced birders who are willing
to teach and encourage you is probably the best way to improve identification
skills rapidly. You can also build your knowledge of species by examining specimens in the collection of a museum and/or university, and through careful
study of reference books and other literature. The number of useful references
is increasing, including:
● illustrated field guides or checklists. For East Africa, the books of
choice are Stevenson & Fanshawe (2001), for the whole region
(except Ethiopia), and Zimmerman et al. (1996), an essential handbook for Kenya and northern Tanzania that includes many birds of
Ugandan forests. Many good guides are available for southern Africa,
such as Sinclair et al. (1997) and Newman (2000). Van Perlo (1999)
covers Zambia, Angola and Mozambique, omitted by most other
127
guides. In West Africa the choice is more limited: Serle & Morel (1992)
covers the whole region but it is out of date (and out of print in
English). There are a few field guides for particular countries, such as
SeneGambia (Barlow et al., 1997) and Sao Tomé and Príncipe
(Christy & Clarke, 1998).
● Birds of Africa, a multi-author, multi-volume handbook published by
Academic Press, and now into its sixth volume (Fry et al., 2000), with
one more volume due. Certainly not one for the field, since each volume weighs several kilograms, but an essential reference work.
● The African Handbook of Birds by Mackworth-Praed & Grant (1955–
1973; six volumes) provides detailed information and is very useful for
identifying birds in the hand, especially where no modern field guide
exists. The nomenclature is somewhat out of date, and the illustrations
are scanty and inadequate, but these volumes remain invaluable.
● Notes on particular difficult groups, in periodicals such as the African
Bird Club Bulletin and Africa: Birds and Birding, or regional publications like Scopus and Kenya Birds (e.g. Allport et al. (1996) on
illadopses, Turner & Zimmerman (1979) and Bennun (1994) on
Kenyan greenbuls).
There are now good commercial compilations of sound recordings for
each major region of Africa: West (by Claude Chappuis); East (by Brian Finch,
published alongside Stevenson & Fanshawe, 2001), and South (by Guy
Gibbon and others). These are very valuable reference sources for forest bird
survey work, and will amply repay study. Bear in mind that there is substantial
individual variation in calls, and that bird species do not always sound the
same across their entire range. Many researchers and birdwatchers also keep
their own sets of recordings and may be willing to loan them; other useful compilations are listed in Pomeroy (1992).
Learning the birds that you are likely to encounter in a specific area, by
sight and sound, will save much time and effort in the field. If you can reliably
detect differences between birds, so that the number of different species you
see can be recorded fairly accurately, this will enable you to collect meaningful
data even if you cannot be sure of all identifications. Indeed, if you find yourself
unable to identify a particular species in the field, even after having consulted a
field guide or birding companion, then it is important to note down important
features of the bird (e.g. general size/colour, beak colour/shape, eye colour,
etc.) or to make a rough sketch. Do not spend too much time doing this,
because the distraction may cause you to miss other sightings. With practice,
your ability to record features of birds in your notes will improve, allowing you
to identify more birds using the reference works.
128
Especially when you are starting off, it may be wise to note which birds
you identify on the basis of their calls alone. This will enable you to go back to
your data and correct your records (in the event of allocating the wrong name
to a particular bird call).
Ideally, you should identify all the birds you record reliably to the level of
species. If you are unable to do so, then try and identify them reliably to the
level of the group or genus (e.g. greenbul or flycatcher). Although birds are
much easier to identify than many other groups of animals, they are still challenging – especially when you are using calls. Always be cautious, and take
your level of experience into account. Never be tempted to name a bird unless
you are really certain of the identification and can justify it from your notes if
necessary. Write down doubtful cases as ‘Unidentified greenbul’ (or whatever),
or in the worst case, ‘Unidentified bird’. Failing to make an identification is
much preferable to making the wrong one.
A note on sampling
A detailed discussion of sample design is beyond the scope of this chapter, and more information on sampling for bird surveys can be found in
Pomeroy (1992) and Bibby et al. (1998). However, some general points are
discussed by Bennun & Fanshawe (1998):
i) Forest bird survey data tend to be noisy. If forests or forest blocks are
to be compared statistically, there must be an adequate number of sampling
units.
ii) This means trying to balance the number of replicates, the time and
effort needed to carry them out, and the size of the sample that can be collected in each case. For instance, if time allows you to run a total of 10km of transects in each block of forest, how should you divide these up? One 10km transect is probably not a good idea, but a hundred 100m transects might not be
useful either – the number of birds you would record along each one might be
very low. Most probably, something in between would be more suitable, with
transect length determined by the number of birds you expect to record and the
number of these transects determined by how much time you have.
iii) Survey results can be strongly influenced by season, time of day and
local habitat variation (including elevation). It is essential to minimise bias in
your data by taking these sources of variation into account (e.g. by conducting
counts at different sites during the same seasons, randomising count order
across the day, and stratifying your sample to take habitat and altitudinal
variation into account).
If you intend to do transect work, or carry out mist netting, you will need
to think about the location of your lines. Usually these should be randomised,
as far as possible, within each stratum of your sample (but if you are mainly
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interested in building up a species list then you will want to place mist nets in a
variety of micro-habitats – also see section 5.3.3). It is often desirable to use
existing small trails and paths, rather than destroying more vegetation by cutting your own. Be aware, however, that trails are themselves often aligned in a
highly non-random way.
Transect lines do not necessarily have to be entirely straight. Some
reconnaissance to map out trails may be necessary (and is almost always useful) before survey work begins. When trails are mapped they can be partitioned
into convenient sections of equal length. By giving each section a number, you
can select sections for sampling using random number tables.
Alternatively, especially if you do have to cut your own trails, you can lay
out transects or mist net lines systematically. For example, you might decide to
sample at every 500m alternately to left and right along a line bisecting the forest. Systematic sampling has the advantage of simplicity and of covering the
whole study site (by definition, random sampling does not always do this).
However, where there is a regular pattern in habitat variation, such as evenly
spaced ridges and valleys for instance, it can potentially lead to biased results.
See also section 7.3.11 for tips on suiting the method to the bird.
7.3.1
General surveys
A general survey consists of recording the species, and sometimes number, of birds seen and heard in an area. After a period of observation, a broad
indication of abundance, such as ‘regular’, ‘common’ ‘rare’, and so on, can be
given to each species.
Site selection, procedure and recording
A regular record is kept of bird species seen and heard during walks (or
at any other time, e.g. around a base camp or while watching a fruiting or flowering tree). Usually, observers try to cover as much of an area as possible and
investigate all major habitats and micro-habitats, in order to maximise the number of species recorded. Observers might also use play-back and mist netting
to try and detect inconspicuous undergrowth species. Preferably, habitat and
numbers (at least for flocking species) should be noted for each record.
Advantages/limitations
This is the least useful approach with respect to quantitative results and
comparative work, but it does allow an initial species list to be drawn up. It is
difficult to standardise observer effort, and impossible to make any but the
broadest comparisons with other sites.
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If a survey is being planned specifically for birds, then it is much better to
use a more systematic approach (such as timed species-counts). If the bird
work is being done as a side-line, perhaps while conducting botanical surveys,
then a general survey may be all that is possible. In any survey it is important
to record ad hoc observations of birds (i.e. casual records in addition to those
on scheduled counts) as these may add substantially to the species list.
7.3.2
Timed species-counts (TSCs)
The timed species-count technique provides a quick and simple method
for gaining a measure of relative abundance of canopy and mid-level bird
species in a fairly large, defined area. It has the advantage of covering a bigger
area than point counts or transects (see below), and it is not tied down to particular localities or lines. Thus it is possible to build up an overall species list
much faster.
TSCs are essentially repeated species lists, on which are indicated the
first time when each species is first positively identified by sight or sound
(Pomeroy & Tengecho, 1986; Pomeroy & Dranzoa, 1997). Species receive a
cumulative score according to when they were first recorded on each count:
species that are observed more frequently receive higher mean scores, as they
tend to occur early within a count as well as in a high proportion of counts.
TSCs were developed initially for use in open habitats, but have been modified
in Kenya for application in forests.
Site selection
As far as possible, TSCs should be well spread over the whole study
area being surveyed. They should also take in all the different micro-habitats
(such as different forest types on ridges and along streams). During the count,
there is no need to keep to a set path, and you can wander off to investigate
sounds of bird activity, fruiting trees, and so on. If you are surveying forest
birds, it is usually a good idea to avoid going into areas of entirely different
habitat, such as grassland or cultivation, as this could obviously give you misleading results. If you have a GPS, it is useful to record the start and end
points of each TSC.
If you work in more than one study site within a forest, you should carry
out the same number of TSCs in each.
Procedure and recording
i) The observer walks slowly and quietly along a path in the forest for a
fixed time period: 40 minutes has been used in Kenya, 60 minutes in Uganda.
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ii) In its simplest version, when the observer positively identifies a particular species for the first time during that count, the species is recorded along
with the time. In the modified version for forests, a note is also made, using a
simple code, as to whether the birds are above or below 3m from the ground,
and whether they are more or less than 25m from the observer’s present position or intended route. In this modified version, it is important to note the first
time the bird is recorded within these limits: i.e. above 3m from the ground and
within 25m from the trail. Only this information is used in calculating the TSC
index. Data may be entered on Form 7.1.
iii) The 3m limit excludes hard-to-detect understorey birds, which this
technique samples inefficiently. The 25m limit removes some of the bias due to
noisy or conspicuous species, which tend to be identified early in a count and
thus receive high scores (Bennun & Waiyaki, 1993). Records outside these limits are still valuable in compiling the overall species list. They can also be used,
if so desired, to calculate an overall occurrence index, i.e. the proportion of
counts on which the species is detected. The 3m limit was developed for use
where undergrowth birds are being sampled by mist netting (see below) and
may be ignored when mist netting is not being used.
iv) In Kenya, the typical procedure has been to carry out at least 20
TSCs for each study area (a particular sector of a forest). Several TSCs may
be carried out in a morning, separated by intervals of at least 10 minutes (in
time) and 100m (in space). Timed species-counts are undertaken by a single
observer, usually after the early peak of morning bird activity has decreased;
this makes the results more consistent, and also allows workers to deal with
the early activity expected at the mist nets (see below). For standardisation
purposes, the suggested count period is between 08:30 and 12:00, but this
may need to be adjusted for different sites. General records of weather conditions (including wind) should be made at the beginning of each count.
v) This exercise should also be repeated as many times as possible,
along different routes. Several people can conduct TSCs along different routes
at the same time.
vi) If using the modified method, you will need to use a simple system of
symbols, or a column on a form, to indicate whether or not the bird is above or
below 3m and within or outside the 25m limit. It may also be a good idea, as
suggested above, to indicate whether the bird was seen (‘s’) or only heard (‘h’).
Data analysis
In the modified method, the TSC index is based on only the records
above 3m and within 25m. To calculate this index, we need to know only the
first time that each species is recorded within these limits; once a species has
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been recorded above 3m and within 25m, there is no need to record it when it
appears again during the same count. For birds recorded outside the limits,
each species need only be recorded once and the time is unimportant. For
each count, each species is then assigned an index ranging from 0 to 4,
depending on whether it was recorded during the first 10 minutes (= 4), second
ten minutes (= 3), down to 0 for a species not recorded during that count. An
average score is then taken over all the counts. For an hour-long TSC, the
scores go from 0 to 6 in the same way. The scores for the two systems can be
made comparable by adding 2.0 to the scores for the 40-minute counts.
Advantages/limitations
The TSC is a good method for assessing relative abundance. It is not
necessary to record the number of birds detected, just the species, and you
can concentrate on detecting new species. This is an advantage for relatively
inexperienced observers who may need to spend more time on identification,
and also for more experienced observers visiting a new site for the first time
and still familiarising themselves with the local birdlife. It is also useful when
trying to cope with mixed-feeding parties, when many species may pass
through in a very short time. The TSC index is a useful comparative measure
of different sites and forests. It is not as good a method as the point count for
detecting shy birds of the forest interior, but appears to be just as efficient (perhaps more so) for sampling canopy species.
Pomeroy & Dranzoa (1997) show that species richness can be assessed
from TSCs either from species accumulation curves or regression estimates.
Measures of relative abundance for individual species from TSCs also correlate
well with those from transect counts (Pomeroy & Dranzoa, 1997) or timed transects (see below: Bennun & Waiyaki, 1993). TSCs produce data on more
species and in less time than traditional transects, thus making them more efficient. Because the TSC does not have to follow a set path over a set distance,
it is much easier to carry out in forests than is a standard line transect. If the
aim is to assess species richness (or the richness of a sub-group of species,
such as forest specialists), or the relative abundance of particular species in
different forests or compartments, then TSCs are a good method to use.
In the unmodified version of TSCs, scores strongly reflect detectability as
well as abundance. They thus cannot be used to compare even the relative
abundance of species that differ widely in their detectability (Pomeroy &
Dranzoa, 1997). This problem is partially overcome by the modified version
with a 25m distance cut-off (Bennun & Waiyaki, 1993). The relative abundance
(compared to other species) of flocking birds is underestimated by TSCs
(Bennun & Waiyaki, 1993), and TSCs do not adequately sample shy understorey birds.
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However, the main problem with TSCs is that the indices are not very
easy to handle mathematically. Each TSC index is a measure of relative
abundance for a particular species on a scale of 0–4 or 0–6. It is not clear
whether TSC scores can legitimately be summed to create a cumulative index
for forest-dependence categories or for guilds. If summed abundance measures for these sub-groups are needed, then it may be better to use another
method – perhaps a timed transect (see below). For this reason, in particular,
TSCs may not be very useful for monitoring purposes (see Bennun &
Fanshawe, 1998).
7.3.3
MacKinnon lists
and related methods
MacKinnon lists (MacKinnon & Phillips, 1993; Bibby et al., 1998) also
allow calculation of an index of relative abundance. In essence, you build up a
picture of the richness of the avifauna and species’ relative abundance by compiling a series of species lists – each with the same number of species. The
faster the total number of species rises as you add lists, the greater the overall
richness. The more lists a particular species occurs on, the more abundant it is.
Fjeldså (1999) developed this method further for use in rapid assessment of forest avifaunas, using a 20-species list.
Site selection
As for timed species-counts. Ideally, your effort should be well spread
across your study site and cover all micro-habitats. Simple MacKinnon listing
requires searching for birds in whatever may be the most efficient manner.
Different ground should be covered from one list to another. The minimum
number of lists needed for each study site is around 15.
The Fjeldså technique involves listing within a defined study site – in his
case, of area 1.5 km2 in a particular forest type. Within this, you walk randomly,
searching for and recording birds.
Procedure and Recording
In the simple version, you search for and record each new bird species
until you have a pre-set number of species on your list – usually between 8
and 20 (the more species-rich your forest, the higher the number on the list
should be). When the species total reaches the pre-set number, start another
list, on which the same species can appear again if you see or hear them.
Fjeldså’s method is similar, but you record every bird seen and heard
throughout the count. Fjeldså walked randomly within the study site from dawn
to dusk, recording throughout. However, the method can just as well be applied
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for shorter periods – the minimum on one day being the time taken to acquire a
list of 20 species.
Data analysis
Plotting the total number of species recorded against the number of lists
included gives a curve that rises rapidly at first and then levels out, finally
reaching a plateau. This plateau level gives the observed species richness,
which can be compared across sites (using the same number of lists, with the
same number of species in each list, for each site). This value is not the same
as the real, total species richness, but can be used to estimate it: Fjeldså
(1999) gives a formula for this, based on Colwell & Coddington (1994).
Relative abundance of species can be expressed as the fraction of lists
on which a species occurs (Bibby et al., 1998). However, since each species
can only occur once on each list, this will severely underestimate the abundance of common species. Fjeldså (1999) dealt with this problem by recording
every bird seen or heard, whether a new species for the list or not. The total
number of records for each species can then be expressed as a percentage of
the overall total. This is a similar approach to the timed transect method (see
below). Relative abundances calculated this way correlated very strongly with
measures derived from intensive point count observation in the same forests
(Fjeldså, 1999).
Advantages/ limitations
The simple MacKinnon list method does not produce reliable relative
abundances, which is a disadvantage for most studies. Fjeldså (1999) lists the
following advantages of the adapted method:
● time is used efficiently – all the time available is devoted to data
collection, rather than, for example, moving between transect lines or
point count points;
● more information is gathered than in a total list of species seen: data
can be standardised and total species richness extrapolated;
● it produces reliable information on relative abundances (provided that
all the birds seen or heard are recorded);
● it is less influenced by the relative skills of observers, compared with
timed species-counts. This is because you can take as much time as
you need to identify a particular bird, and it does not matter whether
you complete your list of 20 species in an hour or in a whole morning.
To obtain relative abundances with this method requires more effort than
with timed species-counts, since all birds seen or heard have to be recorded,
rather than just each new species. The reduced influence of relative skills is
only real if all observers can eventually identify all the birds they see or
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hear – no survey method will work well with very inexperienced observers. With
an experienced survey team, this approach differs very little from timed
transects (see below).
7.3.4
Timed transects (TTs)
Timed transects (TTs) were developed for use in Kenyan forests as a
simple method of assessing relative abundance that did not suffer from some
of the problems of the TSC. Timed transects measure the number of birds seen
in a set time, rather than along a set distance.
Site selection, procedure and recording
The timed transect technique is similar to the TSC, except that the
observer also records the numbers of birds seen or heard within the limits
described for the modified TSC (i.e. above 3m and within 25m), each time a
bird is identified (not just the time a species is first detected). Species detected
outside the limits are recorded separately in order to build up the species total.
Advantages/limitations
Timed transect and TSC scores are strongly correlated (Bennun &
Waiyaki, 1993), and the two methods share the same advantages of being simple and quick to perform. However, because the actual number of birds is
recorded, the timed transect method is less susceptible to the biases of the
TSC index in favour of conspicuous species and against flocking species.
Because the TT index is the actual number of birds detected for each species,
it is straightforward to produce cumulative scores for forest-dependence and
guild categories.
However, TTs require more effort than TSCs. All birds within the limits
must be identified and counted. It can be especially difficult to estimate the
numbers of birds that are only heard – some experience of the forest and the
species may be necessary before this can be done with accuracy.
Timed transects could, in principle, be used for monitoring. However, it is
difficult to repeat exactly the same series of counts in the same places, and to
tie these down to other aspects being monitored (such as vegetation). Point
counts or fixed-length transects are recommended for monitoring instead.
7.3.5
Fixed-width transect counts
Transect counts have been used extensively in open habitats, but, in
closed forest, visibility is poor and the viable transect width tends to be narrow.
It can also be difficult to lay down fixed-length transects in forest habitat. In the136
ory, line transects provide a measure of absolute abundance; in practice, this is
probably not the case, as many birds are probably missed – although the
results of fixed-width transects are expressed as a density.
See the discussion of line transects in the mammals chapters (sections
5.3.3 and 6.3.2).
Site selection
Because transects start and stop at specific points, it is usually possible,
and desirable, to randomise their locations, or to use systematic sampling (e.g.
at fixed distances along a grid). See the section on sampling above.
Procedure and recording
i) You can either use existing trails or grids, or cut your own. Along the
route you have selected, measure out and mark a trail of known length (a useful length might be 1km).
ii) The procedure is to walk the measured route quietly and slowly. The
best time to do this is in the early morning or late afternoon (when birds are
most active), but, in any case, counts should be made at consistent times
across different sites.
iii) Record all the birds you see within a fixed distance of each side of
the selected route: distances between 10m and 25m are feasible depending on
the nature of the habitat (use Form 7.2). If birds are in groups note the number
seen. Record the time and species of each sighting (making notes/sketches of
any birds that you cannot immediately identify). Continue walking the transect
and make sure that you look at all levels, from the ground to the tops of the
trees above the route.
iv) After completing the transect, go back over your notes and attempt to
identify any species you were unable to identify in the field using field guides
and other literature.
Data analysis
Transect data can be used to give a measure of species richness, to calculate diversity indices (see Magurran, 1988 and Pomeroy, 1992 for more information), and to give a density of individual species or categories/guilds within a
defined area of forest. This area is the length of all transects walked multiplied
by the width covered.
Advantages/limitations
Fixed-width transects provide a measure of density (although this will
usually be an underestimate, as many birds may be missed). They also allow
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various diversity indices to be calculated, as there is an abundance associated
with each species. However, this is rarely very useful in practical terms, and the
best measure of diversity is usually simply species richness.
Fixed-width transects are time-consuming and cover a relatively small
area. They are, therefore, not a very efficient way of building up species lists.
They take no account of differences in detectability of species between different habitat types (e.g. disturbed and undisturbed forest), and so can potentially
give misleading density estimates. If reliable density measures of particular
species are required, variable-width transects using distance sampling may be
more useful (see below).
Fixed-width transects can also be difficult to lay down, requiring at least
mapping and measuring, if not extensive cutting of trails. This takes a good
deal of effort and may lead to unnecessary forest disturbance.
7.3.6
Fixed-width point counts
Although excellent for surveys, TSCs and TTs are not really suitable for
monitoring purposes, and point counts have been used for this purpose
(among others) in Kenya. A major problem with this technique, however, is that
very few birds tend to be recorded, since point counts sample a relatively small
area.
Site selection
It is usually easiest to lay out point counts on a grid in a systematic way.
Random locations are also possible, but may be difficult and time-consuming to
find (and re-find) on the ground. You should attempt to make at least 50 point
counts in each study site. In Kenya, a simple method of spacing out counts
was devised. Counts were made along a cut transect every fifteen minutes, i.e.
the observer spent eight minutes walking (fast) along the transect, followed by
seven minutes waiting and counting at the point (see below).
Procedure and recording
i) The observer stands at a pre-determined point that forms the centre of
a count cylinder that extends from forest floor to tree tops. After a two-minute
settling-in period, the next five minutes are spent recording all the birds seen
and heard within a radius of 25m (Form 7.2 may be used). These times can be
varied if necessary. Theoretically, a point count is supposed to detect all the
birds around a point at the moment the count starts. Therefore, there must be a
balance between the time taken to search the area thoroughly, and the likelihood of birds not recorded in the count area moving into it during the count.
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ii) The species and numbers of individuals are recorded for all birds within the limits. Species detected outside the limits can be recorded separately to
build up the species list. It can be useful to record whether birds are above or
below 3m height (regardless of whether mist netting is also being used) so that
undergrowth and higher-level birds can be distinguished. Bird community
changes in response to habitat change can be different at these levels (Bennun
& Fanshawe, 1998).
iii) Point counts should be made over a standard period; for monitoring in
Kenya this has been defined as 09:00 to 11:15, after the main mist netting
activity of the morning (this would mean a maximum of eight counts per
observer per day, following the routine above). Usually, point counts are carried
out by a single observer, but it is possible to have an experienced observer
accompanied by a trainee.
Data analysis
Absolute densities for birds detected within the limits can be calculated
as the total number of birds recorded, divided by the total area covered by the
counts. It is also possible to calculate an occurrence index (the proportion of
counts where a species was recorded, for all birds inside or outside the limits).
Advantages/limitations
Point counts are useful for monitoring because they can be replicated
precisely: counts can be made in more-or-less exactly the same places, in the
same defined area of forest, on a future occasion.
Point counts also have the great advantage that habitat parameters can
be measured around each point, and related to the presence or density of the
birds. For example, Oyugi (1998) used point counts to assess bird abundance
in Kakamega Forest, Kenya. After measuring habitat parameters at each point,
he was able to develop predictive models for the density of various bird
species, and for particular guilds and forest-dependence categories. Similarly,
Fanshawe (1995) used point counts to compare birds in more- and less-disturbed habitats in Arabuko-Sokoke Forest, Kenya.
Point counts sample a relatively small area and the number of individuals recorded for most species on most counts will be zero. This makes it difficult to compare density estimates for particular species statistically. One
approach is to compare the proportions of counts where particular birds were
recorded. This loses important information, however. Another possibility is to
combine density estimates for guilds or forest-dependence categories, or to
sub-sample blocks so that a set of point counts are combined into a single data
point. The small area covered by point counts makes them unsuitable for most
rapid survey work, at least where the main objective is to draw up species lists
and obtain a general idea of the avifaunal composition.
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7.3.7
Distance sampling
Distance sampling provides a powerful set of methods for estimating
absolute abundance of particular species of interest (see Buckland et al.,
1993). Distance methods take into account the fact that many birds that should
be detected during a transect or point count will actually be missed. They also
take into account the fact that birds may not be equally easy to detect in
different forest types.
Owiunji (1996, 2000) used point counts with distance sampling to measure abundance of birds in different forest types in Budongo Forest. Kosgey
(1998) used transects with distance sampling to assess the densities of
Turner’s eremomela, Eremomela turneri, in South Nandi Forest. Similar methods were used by Musila (2001) to census Sokoke pipits, Anthus sokokensis,
and Mulwa (2001) to study Taita white-eye, Zosterops poliogaster. In the
Uluguru Mountains, Tanzania, Tom Romdal (unpubl.) played back calls of the
Uluguru Bush-shrike, Malaconotus alienus, at fixed points, and estimated the
distance of responses.
Site selection, procedure and recording
Distance methods may be used in conjunction with either transects or
point counts. The basic procedure is as described above for fixed-width
methods. However, in this case, there is no cut-off point at a particular distance. Rather, all records (with group sizes) of the species of interest are
noted, together with their perpendicular distance from the transect line, or the
point count observer.
Data analysis
Data are analysed using the programme DISTANCE (the software and
manual are available, free of charge, on the internet at
www.ruwpa.st-and.ac.uk/distance). DISTANCE uses the set of observed distances to model detectability functions (the way in which numbers of records
decline with distance from the observer) and to give estimates of actual densities. Different functions can be obtained for each species and for different habitat types (see also section 5.3.3).
Advantages/limitations
Distance sampling is a very effective and powerful method for a specific
purpose: obtaining reliable estimates of the actual abundance of focal species
(e.g. a particular threatened bird whose population size is unknown). It is
unlikely to be a method of choice for most biodiversity surveys. Obtaining distances for each observation is time-consuming and difficult. For species that
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are rarely encountered, there may not be enough data to model the
detectability functions. Densities can only be obtained for the more frequently
recorded species, and estimating densities for forest-dependence categories
and for guilds will not usually be possible.
Using playback of calls combined with distance sampling can be very
effective for birds (like the aforementioned Uluguru Bush-shrike) that are skulking, scarce, or hard to detect. This does assume, though, that the birds call in
response as soon as they hear the recording. If the birds come closer to you
before responding, the technique may provide biased estimates of abundance.
7.3.8
Mist netting and ringing
All of the above techniques will tend to miss or under-represent forest
understorey birds, which often tend to be difficult to detect and identify visually.
Knowledge of vocalisations can help considerably, but some species are largely silent and others sing only at certain times of the year (see section 4.3.5).
The only means of overcoming this difficulty is to use mist nets. Mist netting and ringing are powerful techniques for surveying and studying birds, and
have been used to follow weight changes, moult, breeding seasons and movement in individual birds. Employing capture-mark-recapture techniques, it can
also be used to estimate population size.
However, mist netting and ringing require considerable expertise and
extreme attention to detail, which can be acquired only through lengthy training. If you will be using mist nets to capture, identify and possibly ring birds,
special permission is required. You should contact the appropriate ringing
scheme (e.g. the Ringing Organiser, East Africa Natural History Society, P.O.
Box 44486, Nairobi) for advice. Mist netting and ringing should be carried out
only by competent and experienced persons and qualified ringers, who can
handle the nets and the birds ethically and safely. If birds are not handled properly, you may affect both the results of your study and, more importantly, the
long-term survival of the population. If you are not a qualified ringer, it is your
responsibility to ensure that at least one and preferably two qualified ringers
are members of your survey team, and that they train others in the proper techniques of netting, handling, and ringing birds.
The nets are called mist nets because they are made of extremely fine
nylon thread and therefore are almost impossible to see when stretched out.
They come in a variety of heights, lengths and mesh sizes, but all feature various numbers of shelves – a pocket of mesh suspended from a strong thread,
which runs along the net. If the nets are set correctly, birds flying across the net
line do not detect them. When they fly into the net, they drop into one of the
mesh pockets, and become entangled (Fig. 7.1). They can then be carefully
removed, identified, banded and measured.
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Fig. 7.1: Examples of mist nets
Equipment
●
●
●
●
●
●
●
●
●
●
●
1
2
mist nets
poles (straight bamboo poles about 40mm in diameter are ideal – light
but strong)
string
bird bags (cloth bags with a draw-string, in which to hold netted birds)
rings (variety of sizes)1
ringing pliers
ringing book (printed books2, or use a hardbound accounting ledger
and label the columns: these data must later be transcribed into the
schedules for the ringing scheme under which you operate; see also
the Ringing Form at the end of this chapter). A waterproof bag is
always advisable.
stop-end ruler
spring balances (sizes 50g max. and 100g max.)
tarpaulin or fly sheet to protect birds and ringers from the elements at
the ringing station
flagging tape (for marking net sites for location before dawn, etc.)
Available from: Ringing Organiser, Nature Kenya, PO Box 44486, Nairobi, Kenya
([email protected]); Ghana Wildlife Society ([email protected]);
Cameroon Ornithology Club ([email protected]).
Contact: Ornithology Department, National Museums of Kenya, P.O. Box 40658,
Nairobi; Kenya.
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Site selection
Mist nets work best when they are set against a background of vegetation. That makes them less visible to birds. Forests usually provide a good
habitat for netting, but open glades and canopy gaps should be avoided. Areas
with a very open understorey usually produce low capture rates too, while nets
close to streams or other water sources are often especially productive. If you
are trying to obtain a representative sample, however, you will need to lay out
your nets along randomly or systematically located lines, stratified according to
major habitat divisions, as explained above.
Procedure
i) To set mist nets, you could use existing (reasonably straight) trails, or
cut runs about 1m wide, if the vegetation will not permit the net to be set as it
is. The aim is not to clear a wide path, or to alter the vegetation, but simply to
let the net be set so that it is not in contact with branches or other vegetation.
The ground over which the net will be placed should also be cleared of any
vegetation or obstacles (such as rocks) that will entangle the net. For a wellillustrated explanation on how to set mist nets, see Howes & Bakewell (1989).
ii) A commonly used size of mist net is 12m in length and 3m high, with
four shelves and a mesh size of about 30mm (1.25in). Longer and shorter
lengths, and various mesh sizes, are also available. It is important to have the
bottom shelf of the net resting close to ground level. Many forest birds are
taken only in the bottom shelf, or the one above it. However, beware of ant
swarms and small mammal predators, which might attack birds trapped close
to the ground – frequent patrolling is important.
iii) The nets must be checked frequently at not less than half-hour intervals (preferably more often), and the birds removed (by trained extractors only)
and placed in cloth bags. The birds are then taken to a ringing station a little
way from the nets (close enough to be convenient, but far enough not to interfere with netting) where they are processed (identified, measured, weighed,
ringed, examined for moult, brood patch, etc.) before release.
iv) Metal rings (termed ‘bird bands’ in North American literature), come in
several different sizes, and the correct size must be fitted to the tarsus of an
individual. Each ring has its own number and instructions on it (e.g. in East
Africa, the message ‘Send Museum Nairobi’). Ringing is not an essential part
of bird surveys using mist nets. However, it is important that captured birds are
marked in some way, so that you can tell if you retrap them. This is usually the
most convenient (and by far the most informative) way of doing so.
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Suggested surveying procedure
i) This procedure has been used successfully for survey by mist nets
(with simultaneous timed species-counts) in Kenya.
ii) The exact number of net sites used and the length of net set up will
vary according to the time available, i.e. the survey schedule, and the particular
forest. The aim is to catch at least 40 birds per net site in order to have a representative sample. Since capture rates vary between forests, so will the netting effort required. For each defined study block, try to net over two sites, each
with between 120–200m of net. Each site is netted for two consecutive mornings. The nets are operated for four hours after dawn each day. This standardisation allows comparison of capture rates per net metre hour. The importance
of using the same time relative to dawn is that bird activity patterns vary greatly
between dawn, mid-day and evening. Experience has shown that capture rate
usually drops off dramatically in the late morning, and that evening capture
rates are usually lower than those of the early morning too.
iii) Nets are set in a straight line with no breaks, along transects cut
through the forest. When possible, it is useful to net along the same transects
as those cut for other studies, such as botanical work. This saves much time
and effort, but it will still probably be necessary to clear the transect further
(especially at ground level) to make it suitable for placing the nets. Mist nets
are set as close to the ground as possible. Nets 18m in length are preferred
(the fewer nets, the less effort), but 9m and 12m long nets can also be used as
needed. These nets have four shelves and are a small mesh size, suitable for
capturing passerine birds.
iv) The number of nets operated could always be increased to give a bigger sample, but this would mean more effort spent in clearing lines, setting up
and moving nets, and would not leave much time to collect important biological
data on the captured birds. The time spent handling each netted bird is obviously a critical factor. Processing very large numbers is usually not feasible for
a survey with limited time and people-power.
Suggested monitoring procedure
i) This procedure has been used for forest bird monitoring by mist nets
(with simultaneous point counts) in Kenya.
ii) For monitoring, one needs to obtain data that can be compared statistically between monitoring sessions. As with the survey, a combination of mist
netting and observation is employed.
iii) The sample unit is the net-line. Six to eight net-lines are operated in
each study area; the more the better, but time is usually a real constraint. Six
net-lines is probably the minimum for a study area.
iv) Each net-line consists of a straight series of nets, continuous along a
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line cut perpendicular to a survey transect (Fig. 7.2). The length of net is
adjusted to ensure a sample of at least 30 birds per net-line. Because of differences in understorey bird density, different lengths of nets will be required at
different localities. In Kakamega, 66m of net were found to be sufficient; in the
Mau forests, 102m were needed. The most suitable length requires some previous experience of the area. In any case, all net lines in a study area should
preferably be of identical length. Two lines are operated at once, which means
that they cannot be too far apart. In Kenya, lines have been cut alternately to
left and right, with around 200m between their starting points. The ringing
station is then based halfway between the two lines.
v) Nets are operated on a strict timetable, again for four hours from
dawn onwards. Records are kept of which site each netted bird comes from
(via a small piece of paper folded into each bird bag). In Kenya, netters have
found no records of birds moving between sites, suggesting that each line is
indeed an independent sample.
Fig. 7.2: Mist net set up line
net line
transect
200m
Recording
i) For each net site, the layout of the nets should be sketched and notes
made of the site location and habitat type and condition.
ii) For each netting session, record the date, the start and end time
(when nets were unfurled and furled), and the weather conditions (see Form
7.3).
iii) For each bird caught during a netting session, it is essential to record
the species, ring number and age and sex (if determined). A number of standard biometric measures are normally taken, including wing length, weight and
the status of moult in the primary wing feathers. Additional biometrics, such as
head and tarsus length, secondary feather, tail and body moult, are also often
recorded. For detailed studies, it can be useful to record in which net, and in
which shelf, particular birds were trapped. The easiest way to do this is to write
the information on a small piece of paper when extracting the bird, then to fold
this and place it in the bird bag. When the bird is removed from the bag so is
the paper, and the details are recorded in the ringing book.
145
iv) Some studies involve taking blood for DNA analysis, putting colour
bands on the birds’ legs to allow individual identification when resighted, or taking repeated measurements to assess fluctuating asymmetry. All this information can be recorded in the ringing book as well.
v) Recaptured birds need to be indicated, usually by means of an ‘R’ in a
circle by the ring number.
Data analysis
As far as survey work goes, the data from mist netting essentially consists of a list of species and the numbers trapped. These can be used as a
means of assessing relative abundance. Catch rates for individual species can
be compared between species and sites if they are expressed as individuals
per 100-metre-net-hours; see Pomeroy (1992) for examples. Within a study,
using a standard length of net for the same hours each day simplifies comparisons. Totals can readily be summed across feeding or nesting guilds.
Species accumulation curves can be drawn using mist net data, plotting
the cumulative number of species against a measure of effort (such as the
number of mist net sessions, or cumulative metre-net hours).
Advantages/limitations
Mist nets are important because currently they are the only method
available to sample birds of the understorey adequately. Mostly using mist nets,
Baker and colleagues (unpubl. data) added some 14 species of forest birds to
the Tanzanian list during fieldwork in Kagera Region, Tanzania. Almost none of
these species had been identified using binoculars, and the presence of many
probably would have gone undetected without the use of mist nets.
The main disadvantages of using mist nets are that they are expensive
to purchase, demand a high degree of training to use properly, and are very
labour-intensive to use requiring substantial time and effort, especially in
cutting net-lines and shifting nets.
Although mist nets allow a standardised approach to surveying understorey birds, they do not sample birds of the mid- and upper canopy. They also
have a number of biases. Capture rates are strongly affected by the time of
day, as mentioned above, so comparisons should be made cautiously if the
approaches have not been standardised. The type of nets and the way they
are set also affects capture rates. For monitoring, or collecting comparative survey data, nets should be of high quality with plenty of pocket, must be in good
condition (holes dramatically reduce the number of captures), and set in a consistent manner (stretched tight between poles, and just off-taut between
shelves). The condition of nets should be checked regularly (at least every half
hour, preferably more often) and any damage repaired (mist nets require
146
considerable maintenance).
Nets do not sample all birds (even small ones) equally. The standard
mist nets also are not suitable for very large, heavy birds, or fast fliers, such as
large parrots, pigeons, and birds of prey. Any ringer will be aware that some
species are more catchable than others. Remsen & Good (1996) showed that
small changes in bird behaviour, e.g. alterations in foraging height following forest disturbance, could potentially cause large changes in capture rates. This
does not invalidate the use of mist nets, but means that results must be
interpreted cautiously. It is another good reason for combining mist netting with
observational work, such as timed transects or point counts. Bear in mind,
however, that a team of at least four is needed if mist netting is to be combined
with counting of canopy birds using point counts.
7.3.9.
Sound recording
The use of tape recorders in bird surveys has not yet been developed as
a standard technique in East Africa, but it has many positive aspects (see
Parker, 1991, for a discussion). The human ear is notoriously selective and
often screens out sounds. However, the tape recorder documents all sounds
detected by the microphone. Recorded sounds can then be later used to identify birds, just as field notes and diagrams can be compared in field guides.
Recorded sounds can also be amplified and played back in order to
attract birds close enough to enable identification. This can be extremely useful
for surveying and monitoring shy and hard-to-see species, especially when
these are scarce and call infrequently. It can be used in an ad hoc way
(recording and playing back calls of birds you have detected but do not recognise) or more systematically (targeted at difficult-to-locate key species).
Small, inexpensive recorders are readily available and can be linked up
with a video-recorder microphone to form a handy, portable system. It is important to use a directional microphone, and to ensure that the system produces
loud enough playback. Though more expensive than tape recorders, mini-disc
systems work very well for sound recording. They are light and portable, store
sound digitally, and offer the great advantage that you can edit and copy your
material almost effortlessly.
Equipment
●
●
●
●
●
high-quality portable tape recorder or mini-disc player
microphone and batteries
blank tapes or mini-discs
recorded tapes/CDs of bird sounds
plastic bag for protecting equipment against moisture
147
Site selection, procedure and recording
For inventory of key species, playback of recordings can be applied in a
systematic way, for instance by playing a recording for a set length of time at a
set volume at a particular point. Any responses by the birds within a set time
period (and, if appropriate, their distance: see also above) can then be noted.
Virani (2000) applied this method to survey Sokoke scops owl, Scops ireneae,
though using a small flute rather than a recorder to imitate their whistled calls.
Systematic playback can also be used for monitoring of one or more target species: the exact points where it is carried out (and the exact time and
volume of playback) then remain fixed between surveys.
For inventories of whole bird communities, Parker (1991) makes the
following suggestions:
i) Get up well before dawn and be out in the area to be surveyed at
least 15 minutes before first light.
ii) Choose a different spot each morning from which to record, preferably
at areas at least 500m apart, and let the recorder run for 15 minutes or more
(depending on the amount of vocal activity). Point the microphone in the direction of louder sounds for at least 60 seconds. Try to record in all directions and
from the undergrowth up to the canopy. Cover as many types of forest and
microhabitats as possible.
iii) Find areas where mixed-species flocks are forming at dawn and
record them for at least 10–15 minutes. Get 5–10 minutes of sounds from any
large flock found at any time of day. (Note: mixed-species flocks are especially
conspicuous in South American forests. Not all African forests have many
mixed-species flocks, nor are these flocks always very vocal.)
iv) Once a comprehensive collection of recordings has been assembled
for a locality, attempt to obtain additional recordings of different individuals and
each species.
Data analysis
Just as for specimens, recordings need to be accurately documented,
and originals or copies deposited in institutions equipped to curate them. See
Form 3.3 for an example of a data sheet used by the Macauley Library of
Natural Sounds at Cornell University, Ithaca, USA. The recordings can be
analysed with respect to numbers of species, time of calling, season of
calling etc.
Advantages/limitations
Recordings (within the physical limits of microphones and tapes/minidiscs) represent a unique way to document avian species diversity. They can
easily be copied and sent to others for research purposes, and also make an
excellent teaching tool.
148
The main limitation is how to keep the equipment from being exposed to
excess heat and humidity. Sophisticated recorders and microphones are also
relatively expensive, but the costs are outweighed by their versatility and the
type of data they are able to collect.
Playback targeted at key species needs to be used sensibly and in a limited way. Birds responding to the tape (or imitated call) do so because they
think they have detected an intruder in their territory. This disrupts their normal
activities. While it is probably not damaging to carry out single surveys, or
repeated monitoring at long intervals, subjecting particular territorial individuals
to frequent playback is unethical and to be avoided.
Bird species respond differently to playback. Some call back but stay
where they are; others come toward the observer and either call or investigate
silently; yet others show no obvious response at all. It is important that you test
the technique on the species you want to target before embarking on a
systematic playback survey.
Using tape recordings for bird community surveys, as done by Parker, is
very time-consuming: you need to spend at least as long analysing the
recording as making it in the first place. Perhaps for this reason the technique
has rarely been used in Africa.
7.3.10
Territory mapping
For detailed population studies, it is, in theory, possible, but very timeconsuming, to map the territory of individual singing males. These are then
plotted on a map of the study site, and give precise information as to density
(e.g. Terborgh et al.,1990).
However, there are many practical difficulties involved. In eastern African
forests, it is sometimes difficult to detect singing males. Furthermore, breeding
seasons are not always as clear cut as in the northern hemisphere, where
there is strong, clear, seasonal breeding and where males are frequently more
visually and vocally conspicuous. Moyer (1993) provides a comparative study
in which densities of forest birds were estimated using territory-mapping, mist
netting and direct counts of non-territorial birds. He concludes that territory
mapping is the most promising method when estimates of territory size and
absolute density of breeding pairs are needed.
7.3.11
Special considerations
Forest birds present a number of challenges to surveyors. Remember to
plan carefully and think clearly about the purpose and objective of your survey,
as this will determine the information that you need to obtain, and thus the
149
methodology that is most appropriate. If you are mainly interested in, for example, shifts of guilds between different forest types, then it will not matter much if
you fail to detect certain cryptic or reclusive species; however, if your focus is
on population sizes of those species, then that is a different matter.
Ideally, you need to know something about the birds you are looking for
before you start. For example, many fruit-eating birds congregate at particular
fruiting trees. If there are only one or two such trees in your area, a standard
transect-based survey might under- or over-estimate abundance. A better
method might be to locate the trees and do a total count of all the frugivores
that are using them.
Very cryptic and silent birds can sometimes only be censused by mist
netting. Some reclusive species show strong seasonal patterns of singing (e.g.
East Coast Akalat, Sheppardia gunningi: Nemeth & Bennun, 2000). Unless you
find out when these times are, you might easily make erroneous comparisons
between sites. Nocturnal birds can often be censused by calls at night, but
again frequently show variations during the night, and within and between
months in their calling activity. This is one of the reasons why surveys need to
be standardised; for instance, all census work might be done during the early
hours of the evening, around full moon, during the dry season.
In tall forests, canopy species can be extremely hard to identify. A telescope can often help, but many birds might still be missed. You need to budget
more time for survey work in tall forests. You should also be careful of comparing population density estimates for canopy birds between low and tall forests.
Species that fly above the canopy are even more of a problem: they might
need to be censused using species-specific techniques, such as counts from
raised points. These are especially useful for birds that fly to and from roosts
each day, like parrots and hornbills.
In some forests, birds form mixed-species flocks – feeding aggregations
of several, often many, different species that move through the vegetation
together. Flocks may move very fast and range over large tracts of forest.
Where mixed-species flocking is common, survey techniques that cover relatively small areas, like point counts, may not work well. With transects or timed
species-counts, moving rapidly through the forest until you locate a flock may
be the best approach. Distance methods can be difficult to apply for mixedspecies flocks. One approach is to try to estimate the distance to the flock centre and calculate the density of flocks, rather than of individual species.
For some scarce species, such as large forest raptors, conventional census methods may be hard to apply. Where these species have big, conspicuous nests, one approach is to locate and count active nests rather than
individual birds.
150
7.4
Specimen handling
Casualties among mist-netted birds should be very rare if the nets are
properly handled, but they do sometimes occur. Although specimen collection
is not usually a goal of surveys, the value of the casualty is maximised if it can
be collected for a museum. Sometimes it may be necessary to take voucher
specimens (for instance, to confirm species identification or range extension, or
if a suspected new taxon is suspected). Specimen preservation is a topic in
itself, and cannot be covered properly here.
Equipment
If voucher specimens or net casualties are to be collected, specimen
collecting permits and material are necessary. For wet specimens:
● 10% formalin or 70% alcohol (c.5 litres)
● container for holding preserved specimens
● hypodermic syringe and needle
For collecting dry specimens, more elaborate equipment (e.g. dissecting
kit, needles and thread, borax powder) is required. Consult museum personnel
or a specialist text on specimen preparation (see Section 4.4).
Procedure and recording
Museums have traditionally favoured skins of birds, but more are now
realising the value of specimens preserved in fluid (10% formalin or 70% alcohol), which is a technique much more suited to the non-specialist. After washing the bird with soapy water to reduce the water repellency of the feathers, it
is immersed in 10% formalin of at least three times the volume of the bird.
A label on waterproof paper, with a numbered code for the specimen,
should be attached to the left tarsus. See Chapter 4 (on small mammals) for
additional information.
Before preserving the specimen, record biometrics and other information,
including soft-part colours (see Fig. 7.4), on the specimen record form (Form
7.4), or in a hardback book. If the specimen is dissected before preservation, it
is important to note the sex and the stomach contents. Specimens are very
valuable and it is worth recording as much information on each one as
possible.
151
Fig. 7.3: Standard measurements for birds
7.5
Health and safety
Very little work seems to have been done on the potential risk to investigators of birds as regards disease transmission, either direct or by arthropod
transmission. Birds do carry ectoparasites such as fleas, mites, and ticks, and
the latter are known to harbour tick-borne diseases that affect humans. It is
prudent for those handling birds to avoid their ectoparasites and to wear surgical gloves and a mask when dissecting specimens and/or preparing study
skins. After handling birds during mist netting and ringing, make sure you wash
your hands thoroughly before eating or drinking.
Bats sometimes become caught in mist nets and need to be carefully
freed. Follow the advice given in Chapter 4 on handling small mammals.
7.6
Conclusions
The following section is adapted from Bennun & Fanshawe (1998, p.16)
and summarises the advice given above on choosing the most appropriate
method:
Choose your methodology carefully. For most survey and monitoring
work, only relative abundance measures are required. Distance-sampling using
variable-width methods (Buckland et al., 1993) is difficult, demanding, and generally only useful for specialised purposes. Because density estimates can be
calculated for only the most common species, compiling data for guilds or forest-dependence categories is difficult. These methods do have the great
advantage that they take into account the relative ease or difficulty of detecting
birds in particular vegetation types. If bird calls are used in conjunction with
sightings, the problem of visual detectability is diminished. Also, if there are big
enough changes in vegetation between sites or monitoring visits to greatly
affect detectability, it is likely that changes in the bird community will be sufficiently large to be picked up with a simple method.
152
Traditional transects can be difficult to place in forests. Timed speciescounts, which do not depend on a straight-line route, are one solution, but they
have substantial disadvantages too. Some of these can be overcome by simple
modification. For comparative survey and monitoring, however, the biggest
drawback concerns the calculated abundance indices, which are not arithmetically tractable – therefore, one cannot simply calculate overall indices for, say,
feeding guilds. Timed transects have been tested in several Kenyan forests,
and combine the flexibility of timed species-counts with the additive indices of a
standard, fixed-width transect.
All of these visual/aural methods work best for canopy and mid-level
birds. For undergrowth species, standardised mist netting is appropriate for
survey and monitoring work, although it is labour-intensive and time-consuming. By confining point counts and timed transects to birds above a certain level
(3m has been used in Kenyan forests), it is possible to differentiate undergrowth and higher-level birds. As the results of these studies show, bird community changes can be different at these two levels. This is to be expected,
given that structural change after logging can affect high- and low-level
vegetation in very dissimilar ways.
153
7.7
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Form 7.1: Timed Species-count Records for Forest Birds
Surveyor:
(total observers):
Field sheet ref:
Date:
(dd/mm/yy)
Altitude:
Aspect:
Address:
Survey site:
Latitude:
Longitude:
UTM (if available):
Vegetation:
Human disturbance:
Season:
Weather:
Lunar phase:
Start time:
End time:
Other:
Time
Species
Within 25m? Above 3m?
Cue = H (heard) or S (seen)
158
Temperature:
Cue
Score
Form 7.2: Bird Recording Sheet for Transect Counts
Surveyor:
(total observers):
Field sheet ref:
Date:
(dd/mm/yy)
Altitude:
Aspect:
Address:
Survey site:
Latitude:
Longitude:
UTM (if available):
Vegetation:
Season:
Human disturbance:
Weather:
Transect length:
Lunar phase:
Start time:
Temperature:
End length:
Other:
Time
Species
No. of birds
in groups
Additional observations:
Write a description on the back of the sheet (noting things such as general size and colour, beak
colour and shape, etc.) for any species you cannot identify with confidence. This can be used later for
comparison with illustrations and descriptions in standard reference works.
159
160
Age
Sex
Wing Head Tarsus Weight
Other
Fat bp
biometrics
Longitude:
Net
Nets open:
Primary Secndry Tail Body
MLT
MLT
MLT MLT
Weather:
Date:
(dd/mm/yy)
Time Init
Notes
Time nets closed:
Time nets open:
If you re-ring a bird, record the original ring number in the Notes column.
Return this original schedule to the ringing organiser – do not send photocopies. The ringing year runs from 01 July to 30 June. All schedules, whether
complete or not, should be sent to the ringing organizer in early July each year but completed schedules may be sent at any time before this to ease the
end-of-the-year paper work. It is most useful if you can prepare and send in a species’ total list covering the schedules submitted.
Ring
#
Species
Latitude:
Location:
Other:
Address:
Collector:
Form 7.3: Bird Mist Netting and Ringing Sheet
Form 7.4: Specimen Records: birds
Specimen reference number:
Collection accession number1:
Collector:
Date:
(dd/mm/yy)
Time:
Address:
Collecting site:
Latitude:
Altitude:
Longitude:
Slope:
Additional notes:
Species:
Sex:
Ectoparasites:
Endoparasites:
Measurements:
Wing (mm) Tarsus (mm) Bill (mm)
Soft part colours
Iris
Bill
Age:
Tarsus
Other:
Moult:
Tissue sample(s) preserved:
Blood sample(s) preserved:
Stomach contents:
Component:
Percentage:
Remarks/Other
1
To be filled in by Museum
161
Foot
Responsible forest management requires accurate information about a
broad range of species. However, time is too short, and resources too
few, for all forest areas to be considered by specialist survey teams.
This manual provides an overview of the methods which can be used to
gather information. It is designed to be carried into the field to guide
survey work, and enable the user to consider the full range of
vertebrates, excluding fish, found in African forests. It also explains the
basic techniques and basic standards needed for the development of
essential inventory and monitoring programmes.
The manual is particularly aimed at:
• people carrying out short reconnaissance surveys and expeditions;
• undergraduate and graduate students carrying out project and
thesis work;
• research departments of forest, wildlife and national parks
departments;
• forest and wildlife managers and technicians with responsibility for
monitoring biodiversity.
Published by Earthwatch
57 Woodstock Road, Oxford, OX2 6HJ, UK
Tel: +44 (0)1865 318825, Fax: +44 (0)1865 311383, Email: [email protected]
www.earthwatch.org/europe
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ISBN No. 0-9538179-4-6
Publication of this manual has been made possible through a generous donation from Rio Tinto plc