Avian habitat and nesting use in the northeast region of the National

__________________
Avian habitat and nesting use in the northeast region of the National
Petroleum Reserve – Alaska
Ikpikpuk River site -2010 report
A report prepared by Joe Liebezeit and Steve Zack of the Wildlife Conservation Society for
The Bureau of Land Management, Alaska Department of Fish and Game, North Slope
Borough, U.S. Fish and Wildlife Service & other interested parties / stakeholders
This document is submitted as an interim report in fulfillment of BLM grant L10AS00057
December 2010
TABLE OF CONTENTS
TABLE OF CONTENTS............................................................................................................ ii
LIST OF FIGURES ................................................................................................................... iii
LIST OF TABLES..................................................................................................................... iv
Executive Summary.................................................................................................................... 1
INTRODUCTION & BACKGROUND..................................................................................... 2
OBJECTIVES ............................................................................................................................. 2
STUDY AREA ........................................................................................................................... 3
METHODS ................................................................................................................................. 3
Study area delineation, plot establishment and setup ................................................................. 3
Species richness and abundance, nest discovery, nest monitoring, and fate assessment ........... 4
Nest predator identification ........................................................................................................ 5
Potential predator abundance and microtine activity.................................................................. 6
Habitat use, vegetative concealment, snow cover, and weather assessment .............................. 6
Data analysis ............................................................................................................................... 6
RESULTS ................................................................................................................................... 8
Relative abundance and diversity of avifauna ............................................................................ 8
Nest density, nest age, nesting success, and nest initiation ........................................................ 8
Nest predator identification ........................................................................................................ 9
Nest predator abundance........................................................................................................... 10
Microtine activity and abundance............................................................................................. 10
Habitat use, vegetative concealment, snow cover, and weather assessment ............................ 10
DISCUSSION........................................................................................................................... 11
ACKNOWLEDGEMENTS...................................................................................................... 13
LITERATURE CITED ............................................................................................................. 13
ii
LIST OF FIGURES
Figure 1. The Ikpikpuk River study site and study plot locations, National Petroleum Reserve,
Alaska, 2010. “ASDN” = Arctic Shorebird Demographics Network.................................. 18
Figure 2. Pictures from the Ikpikpuk River study site, National Petroleum Reserve - Alaska. .. 19
Figure 3. Daily survival rates (± 1 SE) for the three most common nesting species at the
Ikpikpuk River and Prudhoe Bay Oilfield study sites in 2010, Arctic coastal plain, Alaska.
............................................................................................................................................... 20
Figure 4. Mean nest initiation date (± 1 SE) for the three most common nesting birds at the
Ikpikpuk River and Prudhoe Bay Oilfield study sites in 2010, Arctic coastal plain, Alaska.
............................................................................................................................................... 20
Figure 5. Photographic display of the remote camera system used to monitor tundra-nesting
birds for predation events and two images of recorded predation events, Ikpikpuk River
study site, National Petroleum Reserve - Alaska, 2010........................................................ 21
Figure 6. Location of camera-monitored nests and identified predators at subset of nests. ........ 22
Figure 7. Average number of potential nest predators (± 1 SE) detected in or near study plots / 30
min survey period at the Ikpikpuk River and Prudhoe Bay Oilfield study sites, Alaska
Coastal Plain, Alaska, 2010. “Other predators” include Red Fox at both sites and Arctic
ground squirrels at Ikpikpuk only. ........................................................................................ 23
Figure 8. Number of nests found in each landform type within study plots at the Ikpikpuk River
study site, National Petroleum Reserve - Alaska, 2010. Unit 0 = non-patterned ground; Unit
2 = high-centered polygons (≤ 0.5m center-trough relief); Unit 3 = Low-centered polygon
(rim-center relief ≤0.5m); Unit 4 = Low-centered polygon (rim-center relief >0.5m); Unit 5
= Mixed high and low centered polygons; Unit 7 = Strangmoor and/or disjunct polygon
rims; Unit 8 = Hummocky terrain; Unit 9 = Reticulate-patterned ground; Unit A: Alluvial
Floodplain. ............................................................................................................................ 23
Figure 9. Number of nests found in each ecotype class (local-scale ecosystems) as defined by
Jorgensen and Heiner (2003). ............................................................................................... 24
Figure 10. Mean snow cover (%) for survey dates on all plot location fitted with linear trend,
Ikpikpuk River study site, National Petroleum Reserve – Alaska, 2010.............................. 24
Figure 11. Mean daily temperatures (°°C ± 1 SE) during the core breeding season (10 June to 13
July) at the Ikpikpuk River study site, National Petroleum Reserve - Alaska, and the
Prudhoe Bay oilfield study site, 2010. .................................................................................. 25
iii
LIST OF TABLES
Table 1. Bird diversity and relative abundance at the Ikpikpuk River study site, National
Petroleum Reserve - Alaska, 2010........................................................................................ 26
Table 2. Number of discovered nests and nest density for each species from the Ikpikpuk River
study site, National Petroleum Reserve - Alaska, 2010........................................................ 27
Table 3. Summary of daily survival rate (DSR) and Mayfield nesting success estimates of
tundra-breeding birds at the Ikpikpuk River study site, National Petroleum Reserve Alaska, 2010. ........................................................................................................................ 28
Table 4. Nest initiation dates of tundra-nesting birds at the Ikpikpuk River study site, National
Petroleum Reserve, Alaska, 2010. ........................................................................................ 29
Table 5. Summary of camera-monitored nest information at the Ikpikpuk River study site,
National Petroleum Reserve - Alaska, 2010. ........................................................................ 30
Table 6. Date and time of predation events, Ikpikpuk River study site, National Petroleum
Reserve, Alaska, 2010........................................................................................................... 31
Table 7. Average number of all potential predators (and noted absences of other key predators)
recorded during predator surveys for four time periods on and near study plots at the
Ikpikpuk River study site, National Petroleum Reserve - Alaska, 2010. ............................. 32
Table 8. Summary of overhead nest concealment for the most common species (n ≥ 10) and
species groups at the Ikpikpuk River study site, National Petroleum Reserve - Alaska, 2010.
............................................................................................................................................... 33
iv
Executive Summary
In this report we summarize preliminary results from our first year of nesting bird research at the
Ikpikpuk River study site in the NE National Petroleum Reserve – Alaska (NPR-A). The overall
goal of this effort is to provide land managers and other stakeholders (including the BLM, NSB,
ADFG, and others) novel information on breeding birds (and other parameters that may
influence their populations) so that effective management decisions can be made and
implemented to conserve nesting bird populations in the region. In this report we assess key
parameters at the Ikpikpuk site including: breeding species abundance and diversity, nest
density, nest survivorship, nest initiation dates, identity and relative abundance of potential nest
predators, and assess other variables that may influence breeding birds including habitat use,
snow cover, weather conditions, and lemming abundance. We also compare these findings to
those at a site in the Prudhoe Bay oilfields where comparable data were collected in 2010.
We discovered and monitored 184 nests of 18 species from 9 June to 10 July, 2010.
Semipalmated Sandpipers, Lapland Longspurs, and Pectoral Sandpiper nests accounted for the
majority (58%) of those found. Species diversity of nesting birds was higher at Ikpikpuk
compared to Prudhoe Bay (H' = 2.20 vs.1.92, respectively). Overall nest density was also higher
at Ikpikpuk compared to Prudhoe Bay (125.8 vs. 93.3 nests / km2). Among all species, 100 nests
successfully hatched / fledged, 59 failed, and 25 nests were of unknown or undetermined fate.
Nest predation was the most important cause of nest failure (92%). Other sources of nest failure
included abandonment, infertile eggs and trampling likely due to caribou. Passerines (mostly
Lapland Longspurs) had significantly lower survivorship compared to shorebirds. Nest
survivorship was lower at Prudhoe Bay for two of the three most common species compared to
Ikpikpuk, however these differences were not significant.
We used 15 Reconyx camera systems to monitor 35 nests of six species for nest predators.
Fifteen nests successfully hatched / fledged, 13 were predated, six were of unknown fate, and
one nest was still active at the end of the season when the camera was removed. Of the 13
predation events at camera-monitored nests, we identified arctic ground squirrels as the predator
(or likely predator) in nine cases while arctic fox were identified as predators in two cases. Two
predation events were not recorded because the cameras did not trigger. These results suggest
that arctic ground squirrels are the most important predator at the site. This result contrasts with
the predator surveys which identified Glaucous Gulls and Parasitic Jaegers as the most prevalent
potential nest predators. We also observed Long-tailed Jaegers, arctic ground squirrel, and red
fox on the predator surveys. At Prudhoe Bay, Glaucous Gulls and Parasitic Jaegers were also the
most prevalent potential nest predators based on surveys; however the camera evidence indicated
that arctic fox were the most important predator.
In 2010, lemming abundance was low at Ikpikpuk, similar to Prudhoe Bay. Correspondingly,
Pomarine Jaegers, a lemming obligate species, were not observed nesting this year at the site and
were rarely seen after mid-June.
Most birds nested in the “lowland wet meadow” ecotype, which at this site, is comprised
largely of low-center polygon landform type. Lapland Longspurs had higher vegetative
concealment over nests than shorebird species and successful longspur nests had significantly
more concealment than predated nests.
Although overall temperatures at Ikpikpuk seemed particularly cool in June (compared to
previous years at other sites), a warm spike in temperature in early June likely explains the early
snow melt witnessed this year. Snow melt at Ikpikpuk lagged behind Prudhoe Bay and we
correspondingly observed significantly later nest initiation dates at Ikpikpuk.
1
INTRODUCTION & BACKGROUND
The Arctic Coastal Plain (ACP) of Alaska, encompassing a vast region (98,200 km2), supports
internationally important populations of breeding birds during the brief Arctic summer season.
Over 50 species of birds, representing millions of individuals, nest in this region (Johnson and
Herter 1989) including significant populations of shorebirds (Pitelka 1974, Johnson et al. 2007).
In addition, important populations of waterfowl and water birds breed and stage here (King and
Hodges 1979, Earnst et al. 2005). Yet, many of the bird populations that depend so heavily on
their arctic breeding and staging grounds are currently experiencing population declines
including shorebird species (Brown et al. 2001, Morrison et al. 2006) such as the Buff-breasted
Sandpiper (Tryngites subruficollis) and waterfowl including the Spectacled (Somateria fischeri)
and Steller’s Eider (Polysticta stelleri; Stehn et al. 1993, Kertell 1991).
Within the ACP, the National Petroleum Reserve (NPR-A), at 9.5 million hectares, is the
largest piece of public land in the United States and contains a significant portion of Alaska’s
ACP. Because of the disproportionately high density of lakes, ponds, and wet meadows in the
coastal plain region of the NPR-A, this rich habitat includes important nesting and staging
grounds for migratory bird species. This landscape contains a mosaic of wet and dry tundra
habitats, with different bird species tied to each. The NPR-A is also a region of oil development
interest and its eastern boundary lies adjacent to the current oil field infrastructure of Prudhoe
Bay, Kuparuk, and Alpine.
Human activities related to energy development on the ACP may negatively impact nesting
birds by direct loss of habitat through infrastructure expansion, habitat degradation via road dust
and hydrology alteration, vehicle traffic / noise, and pollution (Troy 2000; NAS 2003).
Furthermore, increasing human-subsidized nest predator populations’ can subject nesting birds to
increasing predation pressure (Day 1998, NAS 2003, Liebezeit et al. 2009). On the ACP, known
subsidized nest predators (species that prey on eggs and chicks at active bird nests) include arctic
fox (Alopex lagopus), Glaucous Gull (Larus hyperboreus), and the Common Raven (Corvus
corax). The reported increases in nest predators is thought to be due to the availability of human
food subsidies via landfills, dumpsters, and other sources, and also due to the availability of
artificial den and nest sites, including culverts, towers, and other human structures both in oil
fields and in the villages (Day 1998, NAS 2003). In a recent study, nests of some bird species
were found to have significantly lower nest survivorship within 5 km of oil infrastructure
(Liebezeit et al. 2009).
Although biologists have monitored bird populations on the coastal plain of the NPR-A for
years via aerial surveys (e.g. Larned et al. 2005), information on smaller bird species (such as
shorebirds) is difficult to collect from the air and is therefore underrepresented in previous
studies. Because of the recognized importance of the NPR-A as a breeding ground for nesting
birds, it is critical that land managers have good baseline data to help inform land-use decisions
as oil development will likely expand into this region. Among the most important pieces of
information needed include determining how successful nesting birds are at reproducing young
(nest survivorship), what habitats different species select for nesting, what are the abundances
and identity of nest predators, and how do these parameters compare to nearby anthropogenically
altered areas. In this way, stakeholders in the region will be able to make the most informed
decisions to conserve nesting bird populations in the NE NPR-A.
OBJECTIVES
The overall objective is to determine the habitat use and nesting patterns of tundra nesting birds
at two sites in the NE NPR-A (Ikpikpuk and Teshekpuk), and compare / contrast those patterns
2
with similar data obtained from the oilfields (Prudhoe Bay and Kuparuk). A secondary goal is to
assess predator abundance and identity between the remote Ikpikpuk site and the human-altered
Prudhoe Bay site. The combined data set will provide new information to aid effective wildlife
management by the administrators of the NPR-A (Bureau of Land Management), and other key
stakeholders (e.g. North Slope Borough) in the region. This project also allows us to contribute
toward other collaborative studies (e.g. Arctic Shorebird Demography Network). For this annual
report, we summarize the finding from the first year of the study at the Ikpikpuk study site and
make comparisons to 2010 findings at the Prudhoe Bay oilfield study site. Specifically, we:
1) Summarize nesting biology parameters including breeding species abundance and
diversity, nest density, nest survivorship, and nest initiation dates.
2) Determine the identity of nest predators at Ikpikpuk using remote camera systems and
assess relative abundance of potential nest predators.
3) Assess other variables that may influence nesting birds including habitat use, snow cover,
weather conditions, and microtine abundance.
STUDY AREA
The WCS study site on the Ikpikpuk River is roughly 30 km SSE of the Ikpikpuk River Delta on
the east side of the river (center of the study area is at 70.55343° N, 154.69750° W). The study
area is bordered to the west, east, and north by forks of the Ikpikpuk River. To the south, the
study area is bounded 4 km from our field camp (Figs. 1 & 2). The total area of the study area is
approximately 27 km2.
The study site is within the Arctic Coastal Plain zone of the North Slope which is
characterized by a mosaic of tundra with a gradient of dry, upland tundra, often with high
densities of cotton grass tussocks, to wet and emergent vegetation in the lower areas. The tundra
wetland complex is dominated by numerous ponds and lakes created by the thaw-lake cycle
(Walker et al. 1980). Microrelief is characterized by the presence of high and low polygons,
hummocks, tussocks, and strangmoor / disjuct polygon ridges.
METHODS
Study area delineation, plot establishment and setup
The site and the camp location were selected non-randomly during a reconnoitering visit in June
2009. The criteria we used to select the site included 1) access to an adequate landing area for a
fixed-wing plane equipped with tundra tires, 2) availability of a fresh water source for camp use,
and 3) easy access to suitable nesting habitat for field research. The size of this area was chosen
based on the logistics of our daily work load and maximum distance we could realistically cover
on foot to our study plots. Plot locations were selected by randomly choosing a point within a
grid of points spaced 300 m apart in all cardinal directions across the defined study area. The
first point chosen (omitting points in water bodies and the adjacent flood plains1 around some
lakes) was used as the first plot location. Subsequent plots were placed systematically in relation
to the first plot location. The plots are spatially clustered in groups of four for safety and logistic
reasons. All told, we established 12 10-ha plots (Fig. 1). To determine plot orientation, we first
selected a random compass bearing. If the randomly selected orientation resulted in open water
covering greater than 20% of the plot area, we selected another random orientation until a more
appropriate region was selected.
1
Floodplain areas of some lakes were flooded the first few weeks of the field season
3
ArcGIS 9.3 GIS software was used to aid plot site delineation. We followed plot design
methodology developed by Troy (1996) establishing 10 ha (100 m x 1000 m) plots. Plots were
marked at 50 m intervals along centerline axes using 1.2 m wooden survey stakes; thereby
subdividing the 10 ha plots into 40 50-m x 50-m units. For recording nest locations and
landform type, each unit was further subdivided into four 25-m x 25-m quadrats.
Species richness and abundance, nest discovery, nest monitoring, and fate assessment
We estimated relative species richness and abundance based on casual, non-systematic
observations of all species during our day-to-day activities at work in the field and at rest at our
base camp.
We searched for nests from 12 June to 30 June 2010 from approximately 0900 to 2000
Alaska Daylight Time (AKDT). We used two techniques to discover nests: rope-dragging and
single-person nest searches. The rope-drag technique consists of two observers stretching a 50 m
rope from the plot center to the outer edge and slowly walking while dragging the rope on the
ground, covering the entire plot. When a bird flushes, observers stop long enough to find and
mark the nest. The single-person nest searches are conducted by one observer per plot walking
“W” transects within each plot grid during which attendance to bird behavior leads observers to
nest locations (Troy 1996). To be consistent with our field efforts at other sites, plots were
searched systematically by alternating two rope-drag sessions with two single-person nest
searches (order: rope-drag, single-person, rope-drag, single-person) following a systematic
schedule as defined in the standardized field protocol (Liebezeit 2010). Several nests (n = 21)
were found incidentally (outside of the designated nest search periods while conducting other
field duties) between 9 June and 10 July 2010.
All nests were marked with a plain wooden tongue depressor on which was written the
species, nest identification number and coordinates to the nest. The tongue depressor was placed
approximately 1 m from the nest in the direction of the study plot centerline. A second
fluorescent orange tongue depressor (with the same information as the plain marker) was placed
at the plot centerline to further assist in relocating the nest. At each nest, information including
species, location of nest, nest identification number, observer, date, time, and method of
discovery were recorded onto a data form.
We conducted nest monitor visits systematically every 3-6 d until fates were determined.
Nest monitoring began on 15 June during the first round of rope-drag searches and continued in
tandem with nest searches or independently when necessary. After nest searches ended, we
continued to monitor nests until the end of the field season on 13 July.
We estimated nest fate based on criteria used by other researchers (Troy 1993, Mabee 1997,
Martin et al.1997). A “hatched” nest refers to one that is believed to have successfully hatched
at least one offspring of a nester with precocial young (i.e. shorebirds and waterfowl). A
“fledged” nest refers to one in which at least one nestling was successfully able to leave the nest.
This only applies to the Lapland Longspur (Calcarius lapponicus) and Savannah Sparrows
(Passerculus sandwichensis) since they were the only nesters that produced altricial young at this
site. We assumed a nest hatched / fledged successfully if at least two of the following conditions
were met: the nest was empty within 4 d of the expected hatch date (2 d for passerines), chicks
were observed in the nest or nearby (within 10 m), egg pip holes were observed on the
penultimate visit, and / or other evidence including presence of egg pip fragments (~1-4 mm),
and membranes easily peel away from egg pieces (waterfowl). We assumed predation if the nest
contents were gone at least 4 d prior to the expected hatch / fledge date and / or other evidence
left at the nest indicated predation including large egg-shell pieces with yolk or blood present,
destroyed nest cup, and evidence of previous partial predation. Other potential causes of nest
failure include inclement weather, abandonment due to infertile eggs, trampling by caribou
4
(Rangifer tarandus), and human-induced causes. Nest fate was classified as “unknown” if we
did not have clear evidence or had contradictory evidence as to nest fate. Nests that were still
active when we left the field were classified as “undetermined” fate.
We estimated nest age using one or more of the following methods (1) discovery of an
incomplete clutch during the laying stage and forward-calculating, (2) back-calculating from
hatch day, (3) nestling development (passerines only), or (4) employing the egg flotation
technique (Liebezeit et al. 2007). For extrapolating age of the nest for methods (1) and (2) we
used incubation and nestling stage lengths based on published literature (Poole et al. 2003) and
assumed birds laid one egg per day. We defined nest age as beginning on the day the first egg
was laid until the date the nest was no longer active.
We determined the nestling age of passerines by taking detailed notes on nestling
development at nests of known age and using this information to estimate age at nests found
during the nestling stage. We also used information in the literature on Lapland Longspur
development to assist in aging longspur nestlings (Hussell and Montgomerie 2002).
In order to minimize anthropogenic effects on predation rate we conducted nest checks from
a distance using binoculars (if possible), avoided creating dead-end paths when checking nests,
did not approach an active nest if predators were in the vicinity, did not eat or set equipment
down near active nests, and covered unattended waterfowl nests with vegetation or down.
After nests were no longer active, we determined if they were within the plot using a tape
measure, and we used a Garmin Legend Global Positioning System (GPS) receiver to obtain
geographic coordinates of the nest location (error ± 6 m). We set the GPS units to map datum
WGS 84 and decimal minutes for recording nest locations.
Nest predator identification
From 12 June to 13 July we monitored active shorebird and passerine nests for nest predators
using 15 PC-90 Reconyx motion-triggered camera systems (www.reconyx.com). The camera
systems were mounted on 1.2 m-long 1 cm-wide aluminum dowels secured into the ground or
held directly on the tundra secured with rebar stakes and 18-gauge wire. Cameras were placed
within 5 m of the nest with the infrared beam aligned about 0.15 m above the nest. We
attempted to place cameras >5 m from nests to minimize the likelihood that a given nest predator
would associate camera presence but the units missed some predation events so (with advice
from Reconyx) we decided to place cameras closer to the nests.
We set the camera motion-trigger at a sensitivity setting of “high”. We also enabled the
“rapid-fire mode, so five pictures would be taken upon any event that triggered the motion
sensor. All pictures were recorded on 4-GB compact flash cards. The systems were checked
every 3-4 d and flash cards and batteries were changed when necessary. These camera systems
are easily transportable, weighing <2.5 kg each and five units fit easily in a medium-sized
backpack.
At this site, we set the camera system only on active shorebird and longspur nests that were
in the incubation stage (or nestling stage for longspurs). Cameras were set up on or near the
ASDN2 plots (Fig. 1). Cameras were moved from inactive nests to new nests as soon as
possible. If there was a predation event, we avoided setting up the camera on another nest in the
same area to avoid conditioning potential nest predators to its presence. Within these
parameters, we selected nests opportunistically for camera set-up.
2
ASDN = Arctic Shorebird Demographic Network study plots
5
Potential predator abundance and microtine activity
We conducted three sessions of timed point count surveys on all plots from 17 June to 7 July,
between 0930 and 1800 AKDT. A point count session on each plot consisted of recording all
visual and aural detections of potential predators up to 300 m from the observer during three 10
min surveys from fixed locations (centerline markers) within each study plot (for similar
methodology see Ralph et al. 1993). Each count was conducted at least 10 min and 200 m from
the previous one. We estimated predator distance from the observer (upon the initial sighting) by
using rangefinders, by judging the distance using the plot marker stakes as reference points, or
by pacing the distance on foot. We also noted general behavior and appearance of each predator
to assist in distinguishing individuals from one another to avoid recounting. During each point
count visit observers recorded date, time of arrival on plot, and time of plot departure.
We monitored plots for microtine (lemming and vole) activity by tallying all individual
microtines observed within each plot during predator survey visits. Brown lemmings (Lemmus
sibiricus), collared lemmings (Dicrostonyx torquatus), northern red-backed voles (Myodes
rutilus), tundra voles (Microtus oeconomus), and singing vole (Microtus miurus) are known to
occur on the Arctic coastal plain of Alaska. We did not attempt to identify individuals to species
in most cases because identification can be difficult without close examination of animals in the
hand (Whitaker 1996). We also indirectly assessed mictrotine activity by recording incidental
sightings of Pomarine Jaegers (Stercorarius pomarinus) and Snowy Owls (Bubo scandiaca).
These species are known to nest much more prevalently in years of high lemming abundance and
thus can be an indirect measure of microtine abundance.
Habitat use, vegetative concealment, snow cover, and weather assessment
We assigned the dominant landform type within the designated quadrat (25-m x 25-m
subdivision of plot) of each nest location following the designation of Walker et al. (1980).
These landforms are large-scale, geophysical features that may contain a variety of vegetation
types. For a thorough description of landform types and classification see Liebezeit (2010) –
Appendix J. For nests located outside of the plot boundaries, we estimated landform type within
a 12.5 m radius of a given nest.
We determined the ecotype (local-scale ecosystem) each nest was located in by overlaying
nest location data over a raster map of the “Ecosystems of northern Alaska” map (Jorgensen and
Heiner 2003) using the Hawth’s tool intersect point function in ArcGIS 9.3.
We estimated % overhead vegetative concealment of all shorebird and passerine nests on the
day nest fate was determined using an ocular tube following methods described by James and
Shugart (1970).
From 9 to 29 June, we estimated the percentage of tundra covered by snow to the nearest
10% within each 50-m x 50-m grid of each plot.
From 10 June to 13 July we downloaded hourly relative humidity, air temperature, and wind
speed / direction data, from a HOBO weather station we established at the site (Fig. 2).
Data analysis
We estimated species nest diversity and evenness at the site using the Shannon-Weiner Index.
For this estimate we only used data for nests found within study plots.
We calculated nest density by estimating the number of nests within plot boundaries per unit
area (km2). We estimated nest initiation day by back-calculating from nests of known age to the
date the first egg was laid. For both density and nest initiation estimates we omitted “re-nests”
from the analysis. A re-nest is a second nesting effort by a pair of birds that failed in a previous
6
nesting attempt. We assumed that a nest initiated shortly after another failed within
approximately 100 m of one another indicated a re-nest (but see Naves et al. 2008). We also
assumed re-nesting took place when nests were initiated >14 d after this season’s mean initiation
date for the respective species. None of the species we monitored are believed to re-nest after a
successful nesting attempt with the possible exception of longspurs (see Custer and Pitelka
1977). For both nest density and nest initiation dates we made statistical comparisons between
sites within year (Ikpikpuk and Prudhoe Bay for 2010) using 2-sample T-tests. We employed
appropriate data transformations and / or removed extreme outliers to meet test assumptions (or,
in some cases, we used the equivalent non-parametric tests if the assumptions of normality or
equal variances were not met). Nest density per plot was the sample unit and for nest initiation
date, individual nests were the sample units.
We estimated nesting success using the constant survivorship model in Program MARK
(White and Burnham 1999) which provides estimates of daily survival rate (DSR) and
corresponding standard error estimates (as in Johnson 1979). To calculate the number of days
nests were active (exposure days), for successful nests, we used the period between the estimated
or known initiation date and hatch date. For nests with uncertain fate we used the last observed
active date as the final exposure day to minimize downward bias (Manolis et al. 2000). For
failed nests, Program MARK incorporates probabilities of failure for each day between the last
observed active date and first observed inactive date thus no final exposure day is estimated.
Unlike standard Mayfield estimates, Program MARK does not assume fate day as the midpoint
between the last observed active and first observed inactive date. After DSR was calculated, we
used incubation (and nestling stage) durations reported in the literature (Poole et al. 2003,
Ehrlich et al. 1988) to estimate Mayfield nesting success (Mayfield 1975) for each species3. For
species with sample sizes greater than 10 (Lapland Longspur, Semipalmated Sandpiper [Calidris
pusilla], Pectoral Sandpiper [Calidris melanotos], Greater White-fronted Goose [Anser
albifrons], Red Phalarope [Phalaropus fulicarius]) and for species groups4 we compared DSR
both within and between sites (Ikpikpuk and Prudhoe Bay) with a χ2 test using program
CONTRAST (Sauer and Williams 1989). For all species, we assumed one egg was laid per day,
and that incubation started the day the last egg in the clutch was laid. We defined the beginning
of the nestling stage (for passerines) as the day the first young hatched. Because of the paucity
of nests found in the laying stage for any species, we did not calculate nesting success estimates
for this nesting stage.
We estimated the activity of potential nest predators across the study site by averaging the
number of predator species detections per 30-min time period per plot. We estimated activity
within four time periods defined as “early” (6/20 and before), “middle” (6/21 to 7/5), “late” (7/6
and after) and “season” (all periods). We did not record Artic Tern (Sterna paradisaea) or
Sabine’s Gull (Xema sabini) as potential nest predators. We used the square root transformation
to attempt to normalize predator count data prior to statistical tests (Afifi and Clark 1998). We
compared predator detection differences between sites (Ikpikpuk vs. Prudhoe Bay) for all
predators and for individual species within year (2010) using 2-sample T-tests (or, in some cases,
we used the equivalent non-parametric tests if the assumptions of normality or equal variances
were not met).
3
Mayfield estimates can not be calculated across species groups because incubation lengths for individual species
differ.
4
A major difference between longspur and shorebird nesting success estimates is that longspur estimates include
both the incubation and nestling stage. However, the duration of these combined stages (22 d) is comparable to the
incubation stage length for most shorebirds, thus we felt justified in making these comparisons.
7
We compared nest concealment between species and species groups with adequate sample
sizes (n ≥ 10) using 2-sample T-tests. If the assumptions of normality or equal variances were
not met, we used appropriate data transformations or non-parametric analyses (Afifi and Clark
1998, Zar 1999). We also compared the frequency of landform types and ecotypes types for all
within plot nests and displayed the results as histograms. We used linear regression of % snow
cover per date to estimate trajectory of snow melt until date of completion. We summarized
weather conditions across the time period measured and calculated corresponding standard
errors.
Unless otherwise stated, analyses were conducted using Microsoft Access 2000, Microsoft
Excel, or NCSS 2000 (Hintze 2000). Results are reported as a mean ± SE, and were significant
if P < 0.05.
RESULTS
Relative abundance and diversity of avifauna
From 9 June to 13 July we detected 51 species of birds within the boundaries of the study site
(Table 1). Of these species, 27 were known breeders because we discovered their nests on our
study plots (n = 18; Table 2) or off plot (n = 9; Glaucous Gull, Long-tailed Jaeger [Stercorarius
longicaudus], Parasitic Jaeger [Stercorarius parasiticus], Pacific Loon [Gavia pacifica], Yellowbilled Loon [Gavia stellata], Brant [Branta bernicla], King Eider [Somateria spectabilis],
Sabine’s gull, and redpoll spp [Carduelis spp]). We suspect four other species were nesting in
the area based on behavioral cues or other evidence of nesting (Red-necked Grebe [Podiceps
grisegena], Tundra Swan [Cygnus columbianus], Greater Scaup [Aythya marila], and Spectacled
Eider. Thus, at least 31 species likely breed within the study area.
Compared to Prudhoe Bay, Ikpikpuk nest species diversity was higher (Ikpikpuk: H' = 2.20;
Prudhoe Bay: H' = 1.92) although species evenness was similar between sites (Ikpikpuk=0.76;
Prudhoe Bay=0.80). Nesting shorebird species diversity and evenness were very similar between
sites (Ikpikpuk: H' = 1.62, evenness= 0.74; Prudhoe: H' = 1.62, evenness= 0.77).
Nest density, nest age, nesting success, and nest initiation
Observers discovered and monitored 184 nests of 18 species from 9 June to 10 July, 2010.
Semipalmated Sandpiper, Lapland Longspur, and Pectoral Sandpiper nests accounted for the
majority (58%) of those found (Table 2). Most nests were discovered during rope-drag nest
search visits (96 of 184, 52%). Sixty-seven nests (36%) were discovered using the single-person
search technique. Twenty-one were found incidentally. The average number of nests found in
each study plot was 12.8 with a range of 7 to 17. Overall nest density was 125.8 ± 7.23 SE nests
/ km2 at Ikpikpuk (Table 2) compared to 93.3 ± 10.4 SE at Prudhoe Bay. Overall nest densities
were higher at Ikpikpuk compared to Prudhoe Bay ( T 22 = 2.57, P = 0.02). Semipalmated
Sandpipers had a significantly higher nest density at Ikpikpuk compared to Prudhoe Bay ( T 22 =
2.83, P = 0.01) but no other individual species comparisons indicated any significant differences
in densities between sites.
For breeders with precocial young, most nests were found in the incubation stage (124 of
184, 66%), with 24 other nests found during the laying stage and two nest discovered just after
nest activity terminated. For the one species with semi-precocial young (Arctic Tern), two nest
were found in the incubation stage and the other was discovered in the laying stage. For the two
breeders with altricial young (Lapland Longspurs, Savannah Sparrows), most nests were found
during incubation (23 of 31; 74%), seven were found during laying, and one during the nestling
stage.
8
Among all species, 100 nests successfully hatched / fledged and 59 failed. We were unable
to reliably assess the fate of 15 nests because there was not enough evidence or contradictory
evidence at the nest sites. We were also unable to determine the fate of 10 nests because they
were still active at the end of the field season. Nest predation was the most important cause of
nest failure accounting for 54 of 59 (92%) of failed nests. Other sources of nest failure were
abandonment for unknown reasons (n = 2), failure due to infertile eggs (n = 1), and to trampling
likely by caribou (n = 2).
For the individual species comparisons of inter-specific daily survival rate (DSR), we only
detected a significant difference between longspurs and Semipalmated Sandpipers with
longspurs having a significantly lower survivorship ( X 12 = 7.66, P = 0.006; Table 3). For the
between species group comparison, we only detected a significant difference between passerines
having lower survivorship compared to shorebirds ( X 12 = 4.56, P = 0.03; Table 3). For both
individual species DSR comparisons to Prudhoe Bay (restricted to Lapland Longspur,
Semipalmated and Pectoral Sandpipers for sample size) and for species groups, we found no
differences for any comparison (P > 0.05; Fig. 3).
We determined nest age and nest initiation dates (via forward or back calculations) for the
majority of discovered nests (176 of 184; 96%) using the following methods in order of
importance: egg flotation (n = 54), observed hatch (n = 81), incomplete clutch (n = 21), nestling
age (passerines only; n = 5), and a combination of two of the above methods (n = 15).
Mean nest initiation dates ranged from 8 June for Willow Ptarmigan (Lagopus lagopus; n =
3) to 19 June for Red-necked Phalarope (Phalaropus lobatus; n = 4; Table 4). Compared to
Prudhoe Bay, nest initiation dates for all three species with an adequate sample size at both sites
(n ≥ 10) were significantly different between years with initiation dates trending earlier at
Prudhoe Bay (Lapland Longspur: Z = 5.03, P < 0.001; Pectoral Sandpiper: T 42 = 2.20, P = 0.03;
Semipalmated Sandpiper: Z = -5.41, P < 0.001; Fig. 4). Similarly, for shorebirds and all species
combined, nest initiation dates were significantly earlier at Prudhoe Bay compared to Ikpikpuk
(shorebirds: T 132 = 2.80, P = 0.006; all species: T 163 = 6.10, P < 0.001).
Nest predator identification
We monitored 35 nests of six shorebird species and one passerine species with 15 Reconyx PC90 camera systems from 12 June to 13 July for a total of 408 observation days (Fig. 5; Table 5).
Nests were monitored with cameras throughout the study area although most camera-monitored
nests were in the ASDN study plots (Fig. 6). Fifteen nests successfully hatched / fledged, 13
were predated, six were of unknown fate, and one nest was still active at the end of the season
when the camera was removed.
Of the 13 nests that were predated, images of nest predators were definitely captured at six
nests (four arctic ground squirrel [Spermophilus parryii] and two arctic fox; Table 5). For two
nests we recorded only one image of the potential predator (arctic ground squirrel in both cases).
Because the images did not show the squirrels at the nest or with egg / young, we could not
definitely confirm these as predation events. However, based on timing, these appear to be the
likely predators. At three nests, potential predators (all arctic ground squirrels) were recorded by
the cameras but the time these events were recorded did not correspond to the time of predation
based on nest visits. It is possible that these events were post-predation visits to the nests (or
area near the nests) or they were actual predation events and either the cameras had an erroneous
time setting or the observer recorded the incorrect information on the data forms. To be
conservative, we can only consider these events as “possible predation events”. At two predated
9
nests, the cameras were not triggered so no images were taken. Based on the camera evidence,
arctic ground squirrels appear to be the most important nest predator at this site (Table 5, Fig. 5).
All arctic ground squirrel and one of the two arctic fox predation events occurred diurnally
(between noon and 19:00; Table 6). All of the recorded predation events occurred during the
mid-late period of the nesting season (Table 6).
Nest predator abundance
Five species of potential nest predators were detected during timed point-count surveys. The
most numerous detections were of Glaucous Gulls and Parasitic Jaegers (Table 7). There were
fewer total predator detections at Ikpikpuk compared to Prudhoe Bay (Ikpikpuk: mean = 2.97 ±
0.49; Prudhoe: mean = 3.81 ± 1.03 SE), however this difference was not statistically significant
( T 22 = -1.37, P = 0.18; Fig. 7). Likewise, for individual species comparisons for which we had
adequate data (Glaucous Gulls, Parasitic, and Long-tailed Jaegers), we detected no differences in
abundance between sites. However, ravens were notably absent from Ikpikpuk while the reverse
was true for Arctic ground squirrels (Table 7). We detected no lemming-dependent species
(Snowy owls or Pomarine Jaegers) on incidental counts although they were detected during
informal daily species surveys (Table 1).
Microtine activity and abundance
Microtines were detected only once (likely a vole) during 161.2 hrs of observation time while
visiting our study plots (0.003 ± 0.002 SE lemmings / 30min). At Prudhoe Bay, microtines were
detected at similarly low levels (0.006 ± 0.005 SE lemmings / 30min) thus 2010 appeared to be a
“low” lemming year at both sites.
Habitat use, vegetative concealment, snow cover, and weather assessment
Nests were found in nine of 15 landform types. Most nests (109 of 183, 60%) were located in
low-center polygon landform types (Unit 3: low-centered polygons, rim-center relief >0.5 m and
Unit 4: low-centered polygons, rim-center relief ≤0.5 m; Fig. 8). See Walker (1980) for detailed
description of these landforms.
Most nests in plots were located in the “lowland wet meadow” ecotype (116 of 153; 75.8%;
Fig. 9) with all nests except for two in one of four “meadow” ecotypes. An Arctic Tern nest on a
mat of vegetation within a pond was classified as “lowland lake” and one Black-bellied Plover
(Pluvialis squatarola) nest occurred within the “upland dwarf scrub tundra” ecotype (Fig. 9).
Overall nest concealment for Lapland longspurs was significantly higher than for all
shorebird species with adequate sample sizes (n ≥ 10): Dunlin (Calidris alpina; T 36 = -4.46, P <
0.001), Semipalmated Sandpiper (Z = 5.28, P < 0.001), Red Phalarope (Z = -4.05, P = < 0.001),
and Pectoral Sandpipers ( T 49 = 4.12, P < 0.001; Table 8). Successful longspur nests had
significantly more vegetative concealment above the nest compared to depredated nests (mean
successful = 70.00 ± 4.48 SE vs. mean predated: 45 ± 8.06; T 21 = 2.71, P = 0.01). For shorebirds
as a group, vegetative concealment was not significantly different between successful and
depredated nests (mean successful = 20.55 ± 1.72 SE vs. mean predated: 25.17 ± 4.23; T 39 = 0.55,
P = 0.59).
By the time we conducted our first snow cover surveys at Ikpikpuk on June 9-11, mean snow
cover was just under 4% (Fig. 10). Snow melt at Ikpikpuk seemed to lag behind Prudhoe Bay to
some degree since snow melt was essentially complete by June 9 (Julian date: 160) at Prudhoe
Bay. Because we started snow cover surveys at Ikpikpuk five days later than at Prudhoe Bay it
is difficult to compare the rate of melt between sites. However, anecdotal observations at
10
Ikpikpuk suggest that early season snow melt occurred in an exponential manner as at Prudhoe
Bay (Liebezeit and Zack 2010).
Upon arrival at the site we experienced a brief warm spell followed by cool temperatures
until July (Fig. 11). The mean temperature at Ikpikpuk from 10 June to 13 July was 4.9°C ± 0.49
SE. During this same time period, mean wind speed was 18.25km / h ± 1.02SE coming from the
ESE (124º ± 14.9SE) and relative humidity was 87.21% ± 1.49SE. Mean temperature at Prudhoe
Bay during the same time period was very similar (5.10°C ± 0.66SE). At Prudhoe Bay, 2010
was a relatively cold year (during the breeding season) compared to previous years ranking as
the third coldest year since 2003 so it is likely it was a “cold year” at Ikpikpuk as well.
DISCUSSION
We found a relatively high diversity of breeding birds at the Ikpikpuk river study site with over
31 species that breed or are likely breeders compared to Prudhoe Bay where we observed 21
breeder / likely breeders. Detection of species may have been higher at Ikpikpuk because of the
4-person crew size (vs. 2-person at Prudhoe Bay), although the Prudhoe Bay crew was able to
cover a much larger study area (because of vehicle access) including some habitats (e.g. coastal)
not available to the Ikpikpuk crew. Overall nest density was higher at Ikpikpuk than at other
study sites sampled in recent years on the Arctic Coastal Plain to the east including other nearby
sites in the NE NPR-A (Liebezeit et al. In press, Cotter and Andres 2000). However, nest
densities often vary significantly from year to year in the Arctic (Liebezeit et al. In press) so
multi-year sampling at Ikpikpuk will determine whether it has consistently high nest densities
compared to other sites on the Arctic Coastal Plain.
We found nest predation to be the most important cause of nest failure at this site. This result
is in accord with previous studies that included both the Prudhoe Bay and Kuparuk Oilfields and
sites further east into the Arctic National Wildlife Refuge (Troy 2000, Liebezeit et al. 2009).
Nest predation has also been reported to be the most significant cause of nest failure for
passerines, shorebirds, and waterfowl at many other locations within the arctic coastal plain
(Custer and Pitelka 1977, Quinlan and Lehnhausen 1982, Helmers and Gratto-Trevor 1996). We
found other causes of nest failure to be minimal this season. However, other researchers have
found inclement weather to cause large-scale nest failure in some years (Barry 1962). Caribou
trampling has also been suspected to be an important cause of nest failure in the Prudhoe Bay
region in some years (D. Troy pers. comm.). Daily survival rate (nesting survivorship) was
generally higher at Ikpikpuk compared to Prudhoe Bay although this trend was not statistically
significant. This result is similar to what we found at the nearby Teshekpuk Lake site in
previous years (Liebezeit et al. In press). This provides further support of the importance of the
NE NPR-A for nesting birds compared to adjacent sites to the east. As with nest densities,
survivorship can vary dramatically temporally and between species in the Arctic (Liebezeit et al.
2009, In press) so multiple years of data collection at Ikpikpuk will help determine if this trend is
consistent.
Our predator surveys indicated that the most prevalent potential nest predators at this site
were Glaucous Gulls and jaegers (Parasitic and Long-tailed). This matches what we have
observed at Prudhoe Bay for years (Liebezeit et al. 2009) and also at the Teshekpuk Lake site
(Liebezeit et al. In press). However, it is important to note that these surveys may be biased
toward detecting avian predators because some of the most prevalent mammalian potential
predators (e.g. arctic fox) have been found to be most active nocturnally (Eberhardt et al. 1982).
We detected fewer predators (overall and per species) at Ikpikpuk compared to Prudhoe Bay
although arctic ground squirrels were detected more often at Ikpikpuk. Two species of generalist
nest predators (Common Ravens and arctic fox) were much less common at Ikpikpuk. This may
11
be because these predators are often attracted to human-altered areas, as at the Prudhoe Bay
oilfield.
Our camera evidence of nest predators suggests that arctic ground squirrels are the most
important predator at this site. This is not what we would have expected based on our predator
surveys (see previous paragraph). This finding contrasts markedly from Prudhoe Bay where
arctic fox were the most important predator according to camera evidence. This finding is not
totally unexpected since arctic fox have been reported to be more abundant in the Prudhoe Bay
oilfield compared to surrounding areas (Burgess and Banyas 1993), likely because of the
attraction to human-produced edible wastes. It is possible that some of the predators we
identified with the cameras were responsible for predating more than one nest. In particular, on
3 July two nests that were within approximately 280 m were depredated within 45 min of one
another by an arctic ground squirrel. Home range sizes for male arctic ground squirrels can
range widely across space and time. A study in Yukon, Canada found home range size from
488-2565 m2 (Lacey and Wieczorek 2000). If we assumed a circular territory, the diameter of
the territory would range from ~12-28 m. If arctic squirrel home range sizes are as small as the
ones at the Yukon site, then it is not likely that the same squirrel depredated the nests in question.
Lemmings were observed in low abundance at Ikpikpuk in 2010; the same was true for
Prudhoe Bay. Likewise, Snowy Owls and Pomarine Jaegers did not appear to be in higher
numbers this season. These species are thought to prey almost exclusively on lemmings and are
typically more abundant and nest with higher frequency in high lemming years (Parmelee 1992,
Wiley and Lee 2000).
Overall nesting habitat use at this site was dominated by lowland wet meadow habitats
comprised mainly of the low center polygon landform type. Although in this report we do not
quantify habitat use versus availability, most shorebirds, which are the predominant nester at this
site, typically select wetter tundra habitats (Brown et al. 2007, Liebezeit et al. In press). Thus
this initial examination of habitat use is consistent with previous findings. In our final report we
will examine nesting habitat preference per species and species group. At Prudhoe Bay, lowland
wet meadow ecotype was also the most important habitat for nesting although high-center
polygons and strangmoor were the dominant landform type at that site.
Lapland Longspur nests with higher vegetative concealment were less likely to be
depredated. As one may expect, nest predators are often less successful at finding more
cryptically concealed nests than more exposed ones (Bowman and Harris 1980). However, this
trend was not observed for shorebirds (overall) nor was it documented at Prudhoe Bay for any
species (Liebezeit and Zack 2010). Lapland Longspur nest concealment was significantly higher
compared to Semipalmated and Pectoral Sandpiper nests. This may be due to their differing nest
site selection strategies. Longspurs tend to nest at the base of grass tussocks, on the side of
ridges, or abutting polygon rims (see Rodrigues 1994) while many sandpipers nest in open
scrapes. Because longspurs rear altricial young at the nest, it may be more important for them to
have greater overhead concealment providing cover for the helpless young. In contrast,
precocial sandpipers have cryptically marked eggs and quickly leave the nest upon hatching, thus
may not require as much vegetative cover.
Snow cover appeared to be higher this year in the central Arctic Coastal Plain of Alaska,
compared to recent years, with high snow cover in the first days of June but then rapid melting
(J. Liebezeit pers. obs.). We expected to have earlier snowmelt at Ikpikpuk compared to
Prudhoe Bay since it is located more inland and summer temperatures are typically lower near
the coast on the Arctic Coastal Plain. However, snow melt lagged behind Prudhoe Bay to some
degree. Since temperature differences between sites were negligible, the lag in snow melt at
Ikpikpuk may have been due to higher overall snow depth at this site.
12
Troy (1993) found that snowmelt is strongly correlated with nest initiation. During the short
arctic breeding season, most species tend to initiate nesting as early as possible, thus the main
limiting factor at this time is believed to be snow cover. Accordingly, we found that mean nest
initiation dates for most species were later at Ikpikpuk compared to Prudhoe Bay. Overall, the
nest initiation dates that we documented this season fall within the range found by other
researchers on the North Slope (Custer and Pitelka 1977, Ashkenazie and Safriel 1979, Troy
1993).
ACKNOWLEDGEMENTS
We thank the Bureau of Land Management, Alaska Department of Fish and Game, the Liz
Claiborne / Art Ortenberg Foundation, and the U.S. Fish and Wildlife – NMBCA grant, for
providing funds to support this project. We thank Patagonia for generously donating field
clothing for use by the field crew. We thank Bob Gill and Mike McCrary at 70 North, LLC for
safely and timely getting us in and out of the site. Finally, and most importantly, we thank the
nest monitoring field crew (Kevin Pietrzak, Anaka Mines, McKenzie Mudge, and Nicole Cook)
and the camera tech (Caitlyn Bishop) for their hard work in the field.
LITERATURE CITED
Afifi, A.A. and V. Clark. 1998. Computer-aided multivariate analysis, Third edition. Chapman &
Hall, New York.
Ashkenazie, S. and U.N. Safriel. 1979. Breeding cycle and behavior of the Semipalmated
Sandpiper at Barrow, Alaska. Auk 96: 56-67.
Barry, T.W. 1962. Effect of late seasons on Atlantic Brant reproduction. Journal of Wildlife
Management 26: 19-26.
Bowman, G. B. and L. D. Harris. 1980. Effect of spatial heterogeneity on ground-nest
predation. Journal of Wildlife Management 44: 806-813.
Brown, S., Bart, J., Lanctot, R.B., Johnson, J.A., Kendall, S., Payer, D., and Johnson, J. 2007.
Shorebird abundance and distribution on the coastal plain of the Arctic National Wildlife
Refuge. Condor 109: 1-14.
Brown, S., Hickey, C., Harrington, B., and Gill, R., eds. 2001. United States Shorebird
Conservation Plan, 2nd ed. Manomet, Massachusetts: Manomet Center for Conservation
Sciences.
Burgess, R.M. and P.W. Banyas. 1993. Inventory of Arctic Fox dens in the Prudhoe Bay
region, 1992. BP Exploration [Alaska], Inc. Anchorage, Alaska. Unpublished
report.
Cotter, P.A. and Andres, B.A. 2000. Nest density of shorebirds inland from the Beaufort
sea coast, Alaska. Canadian Field-Naturalist 114: 287-291.
Custer, T.W. and F.A. Pitelka. 1977. Demographic features of a Lapland Longspur population
13
near Barrow, Alaska. Auk 94: 505-525.
Day, R.H. 1998. Predator population and predation intensity on tundra-nesting birds in
relation to human development. Alaska Biological Research Associates, Inc.
Fairbanks, Alaska. Unpublished report.
Earnst, S.L., R.A. Stehn, R.M. Platte, W.M. Larned, and E.J. Mallek. 2005. Population size and
trend of Yellow-billed Loons in northern Alaska. Condor 107: 289-304.
Eberhardt, L.E., W.C. Hanson, J.L. Bengtson, R.A. Garrott, and E.E. Hanson. 1982.
Arctic fox home range characteristics in an oil-development area. Journal of Wildlife
Management 46: 183-190.
Ehrlich, P.R., D.S. Dobkin, and D. Wheye. 1988. The Birder’s Handbook: A field guide to the
natural history of North American birds. Fireside, Simon and Schuster, New York.
Helmers, D.L. and C.L. Gratto-Trevor. 1996. Effects of predation on migratory shorebird
recruitment. Transactions of the 61st North American Wildlife and Natural Resources
Conference.
Hintze, J. L. 2000. Number Cruncher Statistical System (NCSS), version 2000, Kaysville, UT.
Hussell, D.J.T. and R. Montgomerie. 2002. Lapland Longspur (Calcarius lapponicus). In The
Birds of North America, No. 656 (A. Poole and F. Gill, eds.). The Birds of North
America, Inc. Philadelphia, PA.
James, F.C. and H.H. Shugart, Jr. 1970. A quantitative method of habitat description.
Audubon Field Notes, Vol. 24: 727-737.
Johnson, D.H. 1979. Estimating nest success: the Mayfield method and an alternative.
Auk 96: 651-661.
Johnson, J.A., Lanctot, R.B., Andres, B.A., Bart, J.R., Brown, S.C., Kendall, S.J., and Payer,
D.C. 2007. Distribution of breeding shorebirds on the Arctic Coastal Plain of Alaska.
Arctic 60(3): 277-293.
Johnson, S.R. and Herter, D.R. 1989. The birds of the Beaufort Sea. Anchorage: British
Petroleum Exploration (Alaska), Inc.
Jorgensen, T. and M. Heiner. 2003. Ecosystems of Northern Alaska. Unpublished 1:2.5 millionscale map produced by ABR, Inc., Fairbanks, AK and The Nature Conservancy,
Anchorage, AK. (Available at www.nature.org/wherewework/northamerica/states/ alaska
/files/aya2.pdf).
Kertell, K. 1991. Disappearance of the Steller’s eider from the Yukon-Kuskokwim Delta,
Alaska. Arctic 44:177-187.
14
King, J.G. and Hodges, J.I. 1979 A preliminary analysis of goose banding on Alaska’s Arctic
slope. In: Jarvis, R.L., and Bartonek, J.C., eds. Management and biology of Pacific
Flyway geese. Oregon State University Book Stores, Corvallis, Oregon. 176-188.
Lacey and Wieczorek 2000. Territoriality and male reproductive success in arctic ground
squirrels. Behavioral Ecology 12: 626-632.
Larned , W., R. Stehn, and R. Platte. 2005. Eider breeding population survey, Arctic Coastal
Plain Alaska. U.S. Fish and Wildlife Service, Migratory Bird Management, Anchorage,
Soldotna.
Liebezeit, J.R., G.C. White, and S. Zack. In Press. Breeding ecology of birds at Teshekpuk Lake:
a key habitat site on the Arctic Coastal Plain of Alaska. Arctic.
Liebezeit, J.R. 2010. Nest survivorship of tundra-nesting birds in relation to human development
on Alaska’s North Slope – field protocols – 2010. Unpublished document. 42p.
Liebezeit. And S.W. Zack. 2010. Avian habitat and nesting use of tundra-nesting birds in the
Prudhoe Bay Oilfield – Long-term monitoring: 2010 annual report. Prepared by the
Wildlife Conservation Society for the Bureau of Land Management, Alaska Department
of Fish and Game, BP exploration (Alaska), Inc., & other interested parties/stakeholders.
37 p.
Liebezeit, J.R., P.A. Smith, R.B. Lanctot, H. Schekkerman, I. Tulp, S.J. Kendall, D.M. Tracy,
R.J. Rodrigues, H. Meltofte, J.A. Robinson, C. Gratto-Trevor, B.J. McCaffery, J. Morse,
and S.W. Zack. 2007. Assessing the development of shorebird eggs using the flotation
method: species-specific and generalized regression models. Condor 109: 32-47.
Liebezeit, J.R., S.J. Kendall, S. Brown, C.B. Johnson, P. Martin, T. McDonald, D. Payer, C.L.
Rea, B. Streever, A.M.Wildman, and S. Zack. 2009. Influence of human development and
predators on nest survival of tundra birds, Arctic Coastal Plain, Alaska. Ecological
Applications 19: 1628-1644.
Mabee, T. 1997. Using eggshell evidence to determine nest fate of shorebirds. Wilson Bulletin
109: 307-313.
Manolis, J.C., D.E. Andersen, and F.J. Cuthbert. 2000. Uncertain nest fates in songbird
studies and variation in Mayfield estimation. Auk 117: 615-626.
Martin, T.E., C. Paine, C.J. Conway, W.M. Hochachka, P. Allen, and W. Jenkins. 1997.
Breeding Biology Research and Monitoring Database (BBIRD). Montana Cooperative
Wildlife Research Unit. Missoula, MT.
Mayfield, H.F. 1975. Suggestions for calculating nest success. Wilson Bulletin 87: 456-466.
Morrison, R.I.G., McCaffery, B.J., Gill, R.E., Skagen, S.K., Jones, S.L., Page, G.W., GrattoTrevor, C.L., and Andres, B.A. 2006. Population estimates of North American shorebirds,
2006. Wader Study Group Bulletin 111:67-85.
15
NAS. 2003. Cumulative environmental effects of oil and gas activities on Alaska’s North Slope.
National Research Council of the National Academies. National Academies Press,
Washington D.C.
Naves, L.C., R.B. Lanctot, A.R. Taylor, and N.P. Coutsoubos. 2008. How often do arctic
shorebirds lay replacement clutches? Wader Study Group Bulletin 115(1): 2-9.
Parmelee, D.F. 1992. Snowy Owl (Nyctea scandiaca). In The Birds of North America, No. 10.
(A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Pitelka, F.A. 1974. An avifaunal review for the Barrow region and North Slope of Alaska.
Arctic Alpine Research 6: 161-184.
Poole, A.F., Stettenheim, P., and Gill, F.B., eds. 2003. The Birds of North America: Life
Histories for the 21st century. The Academy of Natural Sciences, Philadelphia, and The
American Ornithologists’ Union, Washington, D.C.
Quinlan, S.E. and W.A. Lehnhausen. 1982. Arctic Fox, Alopex lagopus, Predation on nesting
Common Eiders, Somateria mollissma, at Icy Cape, Alaska. Canadian Field-Naturalist
96: 462-466.
Ralph, C.J., G.R. Geupel, P. Pyle, T.E. Martin, and D.F. DeSante. 1993. Handbook of
field methods for monitoring landbirds. Gen. Tech. Rep. PSW-GTR-144. Albany,
California: Pacific Southwest Research Station, Forest Service, U.S. Department of
Agriculture. 41 p.
Rodrigues, R. 1994. Microhabitat variables influencing nest-site selection by tundra birds.
Ecological Applications 4: 110-116.
Sauer, J. R., and B. K. Williams. 1989. Generalized procedures for testing hypotheses about
survival or recovery rates. Journal of Wildlife Management 53:137-142.
Stehn, R.A., Dau, C.P., Conant, B., and Butler, W.I. 1993. Decline of Spectacled Eiders nesting
in western Alaska. Arctic 46: 264-277.
Troy, D.M. 1993. Population dynamics of birds in the Pt. McIntyre reference area, 1981-1992.
Troy Ecological Research Associates Prepared for BP Exploration [Alaska], Inc.
Anchorage, Alaska. Unpublished report.
Troy, D.M.1996. Population dynamics of breeding shorebirds in Arctic Alaska. International
Wader Studies 8: 15-27.
Troy, D.M. 2000. Shorebirds In The Natural History of an Arctic Oil field, Development and the
Biota (J.C. Truett and S.R. Johnson, eds.). Academic Press, San Diego, CA.
Walker, D.A., K.R. Everett, P.J. Webber, and J. Brown. 1980. Geobotanical atlas of the Prudhoe
Bay region, Alaska. United States Army Corps of Engineers. Cold Regions Research and
Engineering Laboratory. CRREL report 80-14. Hanover, NH.
16
Whitaker, J.O. 1996. National Audubon Society Field Guide to North American Mammals.
National Audubon Society. Random House, Inc.
White, G.C. and K. P. Burnham. 1999. Program MARK: Survival estimation from populations
of marked animals. Bird Study 46 Supplement, 120-138.
Wiley, R.H., and D.S. Lee. 2000. Pomarine Jaeger (Stercorarius pomarinus). In The Birds of
North America, No. 483. (A. Poole and F. Gill, eds.). The Birds of North America, Inc.,
Philadelphia, PA.
Zar, J.H. 1999. Biostatistical analysis. 4th edition. Prentice Hall, NJ.
17
Figure 1. The Ikpikpuk River study site and study plot locations, National Petroleum
Reserve, Alaska, 2010. “ASDN” = Arctic Shorebird Demographics Network.
18
Aerial view of WCS Ikpikpuk camp and field site in
early June shortly after arrival. Photo: C. Smith
WCS Ikpikpuk camp. Photo: C. Bishop
WCS field assistants (Anaka Mines & McKenzie
Mudge) conducting field work on nest monitoring plot
4. Photo: J. Liebezeit
Weather station at Ikpikpuk camp. Photo: J.
Liebezeit
Kevin Pietrzak, crew leader of the nest monitoring
crew. Photo: McKenzie Mudge
Semipalmated Sandpiper, the most common nester at
Ikpikpuk. Photo: N. Cook
Figure 2. Pictures from the Ikpikpuk River study site, National Petroleum Reserve - Alaska.
19
1
Nest daily survival rate
0.99
0.98
0.97
0.96
0.95
0.94
0.93
Lapland Longspur
Semipalmated Sandpiper
Pectoral Sandpiper
0.92
0.91
0.9
Prudhoe Bay
Ikpikpuk
Figure 3. Daily survival rates (± 1 SE) for the three most common nesting
species at the Ikpikpuk River and Prudhoe Bay Oilfield study sites in 2010,
Arctic coastal plain, Alaska.
165
Julian date
163
161
159
157
155
Lapland Longspur
Semipalmated Sandpiper
Pectoral Sandpiper
153
Ikpikpuk
Prudhoe Bay
Figure 4. Mean nest initiation date (± 1 SE) for the three most common nesting
birds at the Ikpikpuk River and Prudhoe Bay Oilfield study sites in 2010, Arctic
coastal plain, Alaska.
20
Reconyx PC90 camera system. Photo: C.
Bishop
Caitlyn Bishop (camera technician) and Vitek Jirinec checking one
of the Reconyx cameras. Photo: C. Smith
Arctic fox raiding a Semipalmated Sandpiper nest, July 10, 2010 at
02:56.
Arctic ground squirrel eating a Red Phalarope
egg, July 7, 2010 at 15:15.
Figure 5. Photographic display of the remote camera system used to monitor tundra-nesting
birds for predation events and two images of recorded predation events, Ikpikpuk River study
site, National Petroleum Reserve - Alaska, 2010.
21
Figure 6. Location of camera-monitored nests and identified predators, Ikpikpuk River study
site, National Petroleum Reserve - Alaska, 2010.
22
4
other predators
Arctic Fox
Avg. # preds. detected / 30 min.
3.5
Common Raven
Long-tailed Jaeger
3
Parasitic Jaeger
Glaucous Gull
2.5
2
1.5
1
0.5
0
Ikpikpuk
Prudhoe Bay
Most common potential nest predators
Figure 7. Average number of potential nest predators (± 1 SE) detected in or near study
plots / 30 min survey period at the Ikpikpuk River and Prudhoe Bay Oilfield study sites,
Alaska Coastal Plain, Alaska, 2010. “Other predators” include Red Fox at both sites and
Arctic ground squirrels at Ikpikpuk only.
80
Number of nests
70
60
50
40
30
20
10
0
Unit 0 Unit 2 Unit 3 Unit 4 Unit 5 Unit 7 Unit 8 Unit 9 Unit A
Landform type
Figure 8. Number of nests found in each landform type within study plots at the Ikpikpuk
River study site, National Petroleum Reserve - Alaska, 2010. Unit 0 = non-patterned ground;
Unit 2 = high-centered polygons (≤ 0.5m center-trough relief); Unit 3 = Low-centered polygon (rim-center
relief ≤0.5m); Unit 4 = Low-centered polygon (rim-center relief >0.5m); Unit 5 = Mixed high and low
centered polygons; Unit 7 = Strangmoor and/or disjunct polygon rims; Unit 8 = Hummocky terrain; Unit 9 =
Reticulate-patterned ground; Unit A: Alluvial Floodplain.
23
Number of nests
120
100
80
60
40
20
0
Lowland lake Lowland Moist Lowland Wet Riverine Moist Riverine Wet Upland Dwarf
Meadow
Meadow
Meadow
Meadow
Scrub Tundra
Habitat Class
Figure 9. Number of nests found in each ecotype class (local-scale ecosystems) as defined
by Jorgensen and Heiner (2003) at the Ikpikpuk River study site, National Petroleum
Reserve - Alaska, 2010.
18
Mean snow cover (%)
16
2
R = 0.1112
14
12
10
8
6
4
2
0
158
163
168
173
178
Julian date
Figure 10. Mean snow cover (%) for survey dates on all plot location fitted with linear trend,
Ikpikpuk River study site, National Petroleum Reserve – Alaska, 2010.
24
o
Mean daily temperature ( C)
20
18
16
14
Ikpik average temp (°C)
PB average temp (°C)
12
10
8
6
4
2
0
6/9/2010
6/14/2010 6/19/2010 6/24/2010 6/29/2010
7/4/2010
7/9/2010
7/14/2010
Date
Figure 11. Mean daily temperatures (°C ± 1 SE) during the core breeding season (10
June to 13 July) at the Ikpikpuk River study site, National Petroleum Reserve Alaska, and the Prudhoe Bay oilfield study site, 2010.
25
Table 1. Bird diversity and relative abundance at the Ikpikpuk River study site, National
Petroleum Reserve - Alaska, 2010.
Abundance* Species
Species
Abundance*
U
Red-throated Loon (Gavia stellata)
C
Pacific Loon (Gavia pacifica)
Yellow-billed Loon (Gavia adamsii)
Red-necked Grebe (Podiceps
grisegena)
Tundra Swan (Cygnus columbianus)
Cackling Goose (Branta hutchinsii)
Brant (Branta bernicla)
Greater White-fronted Goose (Anser
albifrons)
Snow Goose(Chen caerulescens)
C
F
F
R
F
A
R
A
R
R
Green-winged Teal (Anas crecca)
F
Greater Scaup (Aythya marila)
King Eider (Somateria spectabilis)
F
U
Spectacled Eider (Somateria fischeri)
Long-tailed Duck (Clangula hyemalis)
Red-breasted Merganser (Mergus
serrator)
Northern Harrier (Circus cyaneus)
Golden Eagle (Aquila chrysaetos)
Bald Eagle (Haliaeetus leucocephalus)
Merlin (Falco columbarius)
C
R
Ruddy Turnstone (Arenaria interpres)
Dunlin (Calidris alpina)
Pectoral Sandpiper (Calidris melanotos)
Semipalmated Sandpiper (Calidris
pusilla)
Stilt Sandpiper (Calidris himantopus)
Long-billed Dowitcher (Limnodromus
scolopaceus)
Red Phalarope (Phalaropus fulicaria)
Red-necked Phalarope (Phalaropus
lobatus)
Long-tailed Jaeger (Stercorarius
longicaudus)
Parasitic Jaeger (Stercorarius parasiticus)
Pomarine Jaeger (Stercorarius
pomarinus)
Glaucous Gull (Larus hyperboreus)
R
A
A
A
U
C
A
A
C
C
U
A
F
Sabine’s Gull (Xema sabini)
R
C
R
R
R
A
Willow Ptarmigan (Lagopus lagopus)
Sandhill Crane (Grus canadensis)
Black-bellied Plover (Pluvialis
squatarola)
R
A
R
Peregrine Falcon (Falco peregrinus)
Rock Ptarmigan (Lagopus mutus)
F
Bar-tailed Godwit (Limosa lapponica)
Northern Pintail (Anas acuta)
Northern Shoveler (Anas clypeata)
American Golden-plover (Pluvialis
dominica)
Semipalmated Plover (Charadrius
semipalmatus)
Whimbrel (Numenius phaeopus)
C
R
Arctic tern (Sterna paradisaea)
Short-eared Owl (Asio flammeus)
Snowy Owl (Bubo scandiacus)
Yellow Wagtail (Motacilla flava)
Savannah Sparrow (Passerculus
sandwichensis)
White-crowned Sparrow (Zonotrichia
leucophrys)
Lapland Longspur (Calcarius lapponicus)
Repoll sp. (Carduelis spp)
A
R
R
R
C
R
A
F
C
*(A) Abundant: Easy to find in large numbers on any given day in a variety of habitats; (C) Common: Easy to find in good
numbers on any given day in suitable habitat; (F) Fairly common: Likely to find in small numbers on most days in suitable
habitat; (U) Uncommon: Possible to find in small numbers on one in four days in suitable habitat; (R) Rare: Seldom found in
any numbers even in suitable habitat.
(X) Extremely rare: Found only in some years and only one or two occurrences in the season.
26
Table 2. Number of discovered nests and nest density for each species from the Ikpikpuk River
study site, National Petroleum Reserve - Alaska, 2010.
Species
Species Code
Discovered
Nestsa
Nest densityb
(nests/km2)
Semipalmated Sandpiper (Calidris pusilla)
SESA
56 (45)
36.7
Lapland Longspur (Calcarius lapponicus)
LALO
29 (27)
21.7
Pectoral Sandpiper (Calidris melanotos)
PESA
22 (17)
14.2
Greater White-fronted Goose (Anser albifrons)
GWFG
19 (17)
14.2
Red Phalarope (Phalaropus fulicaria)
REPH
15 (14)
11.7
Dunlin (Calidris alpina)
DUNL
10 (7)
5.8
Long-billed Dowitcher (Limnodromus scolopaceus)
LBDO
8 (2)
5.0
Red-necked Phalarope (Phalaropus lobatus)
RNPH
4 (4)
3.3
Black-bellied Plover (Pluvialis squatarola)
BBPL
4 (3)
2.5
Willow Ptarmigan (Lagopus lagopus)
WIPT
4 (3)
2.5
Arctic Tern (Sterna paradisaea)
ARTE
3 (3)
2.5
American Golden-plover (Pluvialis dominica)
AMGP
2 (1)
0.8
Savannah Sparrow (Passerculus sandwichensis)
SAVS
2 (1)
0.8
Bar-tailed Godwit (Limosa lapponica)
BARG
1 (1)
0.8
Long-tailed Duck (Clangula hyemalis)
LTDU
1 (1)
0.8
Northern Pintail (Anas acuta)
NOPI
1 (1)
0.8
Greater Scaup (Aythya marila)
GRSC
1 (1)
0.8
Rock Ptarmigan (Lagopus mutus)
ROPT
1 (1)
0.8
184 (153)
125.8
Total
a
( ) = Nests found within the plot boundaries
Nest density calculated from nests excludes off- plot nests and second nesting attempts (Lapland Longspur:
10KWP044; Semipalmated Sandpiper: 10KWP049; n = 151).
b
27
Table 3. Summary of daily survival rate (DSR) and Mayfield nesting success estimates of tundrabreeding birds at the Ikpikpuk River study site, National Petroleum Reserve - Alaska, 2010.
na
Mayfieldb
Daily
survival
ratec
SE
Statistically
different from
(at α 0.05)
Semipalmated Sandpiper
45
0.801
0.989
0.004
LALO
Lapland Longspur
28
0.358
0.954
0.012
SESA
Pectoral Sandpiper
17
0.583
0.976
0.010
none
Greater White-fronted Goose
16
0.608
0.980
0.008
none
Red Phalarope
14
0.655
0.978
0.011
none
Dunlin
7
0.649
0.980
0.014
-
Long-billed Dowitcher
6
0.554
0.973
0.019
-
Phalaropes
18
-
0.974
0.011
none
Waterfowl
19
-
0.975
0.009
none
Passerines
29
-
0.956
0.011
shorebirds
Shorebirds
98
-
0.981
0.004
passerines
Shorebirds, passerines,
waterfowl
145
-
0.976
0.003
none
Species
Individual species
Species groups
a
This estimate excludes nests outside of the study plots and nests that failed due to human disturbance. Only
included individual species estimates if n ≥5.
b
All estimates are for incubation period only except passerines (Lapland Longspurs, Savannah Sparrows) which
includes both incubation and nestling periods.
C
Program MARK constant daily survivorship model used to calculate daily survival rate and corresponding
standard error estimates.
28
Table 4. Nest initiation dates of tundra-nesting birds at the Ikpikpuk River study site, National
Petroleum Reserve, Alaska, 2010.
Minimum
Maximum
28
Mean initiation date ±
1 SE
10 June ± 0.92
1 June
23 June
Semipalmated Sandpiper
21
10 June ± 0.39
2 Jun
22 June
Pectoral Sandpiper
23
12 June ± 0.67
7 June
20 June
Red-necked Phalarope
4
19 June ± 2.50
14 June
24 June
Red Phalarope
15
12 June ± 1.10
5 June
23 June
Dunlin
10
10 June ± 1.35
7 June
21 June
Greater White-fronted Goose
17
9 June ± 0.54
5 June
13 June
Long-billed Dowitcher
8
10 June ± 1.49
6 June
17 June
Black-bellied-plover
4
15 June ± 0.65
13 June
16 June
Willow Ptarmigan
3
8 June ± 1.53
6 June
11 June
American Golden-plover
2
18 June ± 6.00
12 June
24 June
Arctic Tern
2
12 June ± 0.50
11 June
12 June
Savannah Sparrow
2
14 June ± 0.50
13 June
14 June
Bar-tailed Godwit
1
24 June
-
-
Northern Pintail
1
19 June
-
-
Species*
n
Lapland Longspur
* This estimate includes off-plot nests but excludes nests of unknown age and likely second nesting attempts (see
Table 2).
29
Table 5. Summary of camera-monitored nest information at the Ikpikpuk River study site,
National Petroleum Reserve - Alaska, 2010.
Prey species
Semipalmated
Sandpiper
1
Number of
nests
monitored
10
Lapland
Longspur
10
Pectoral
Sandpiper
4
Red Phalarope
4
Camera
monitor
days
142
184
20
32
Fate
Definite
predator
4 Hatch
4 Predation
2 Unknown
7 Fledge
3 Predation
Likely
predator
ARFO1
AGSQ
AGSQ,
ARFO
AGSQ1
AGSQ
3 Unknown
1 Predation
2 Hatch
2 Predation
Dunlin
3
12
2 Hatch
1 Predation
Red-necked
Phalarope
3
12
2 Predation
1 Unknown
Long-billed
Dowitcher
1
6
Undetermined
TOTAL
34
408
15 hatch/fledge
13 Predation
6 Unknown
1 Undetermined
ARFO = Arctic Fox; AGSQ = Arctic ground squirrel
30
Possible
predator
AGSQ
AGSQ
AGSQ
AGSQ
AGSQ
4 AGSQ
2 ARFO
2 AGSQ
3 AGSQ
Table 6. Date and time of predation events, Ikpikpuk River study site, National Petroleum
Reserve, Alaska, 2010.
Date of predation1
10CJS019
Predator
species
AGSQ
7/5/10
Time of
predation1
15:022
Red Phalarope
10CJS048
AGSQ
7/7/10
13:32
Semipalmated Sandpiper
10MLM003
AGSQ
6/24/10
18:52
Lapland Longspur
10VJ002
AGSQ
6/20/10
18:45 – 19:48
Red-necked Phalarope
10VJ008
AGSQ
7/7/10
15:12 – 15:15
Lapland Longspur
10VJ011
AGSQ
6/19/10
12:08
Red Phalarope
10VJ059
AGSQ
7/3/10
13:18
Dunlin
10VJ065
AGSQ
7/3/10
14:01
Pectoral Sandpiper
10VJ053
AGSQ
7/4/10
14:35 – 14:36
Semipalmated Sandpiper
10VJ086
ARFO
7/10/10
14:563
Lapland Longspur
10VJ096
ARFO
7/8/10
03:01
Prey species
Nest ID
Semipalmated Sandpiper
1
includes “likely” or “possible” predators.
AGSQ visit also recorded the next day (7/6/10) at 10:27-28
3
ARFO visit also recorded the next day (7/11/10) at 06:54
2
31
Table 7. Average number of all potential predators (and noted absences of other key predators) recorded during predator surveys for
four time periods on and near study plots at the Ikpikpuk River study site, National Petroleum Reserve - Alaska, 2010.
Earlya
Speciesb
Mean ± 1 SE / 30 min count
Middle
Mean ± 1 SE / 30 min count
Late
Season
Mean ± 1 SE / 30 min count Mean ± 1 SE / 30 min count
32
Glaucous Gull
1.50 ± 0.44
1.58 ± 0.45
1.67 ± 0.41
1.58 ± 0.38
Parasitic Jaeger
0.67 ± 0.40
0.92 ± 0.29
0.42 ± 0.29
0.67 ± 0.17
Pomarine Jaeger
0
0
0
0
Long-tailed
Jaeger
0.25 ± 0.18
0.58 ± 0.23
0.25 ± 0.13
0.36 ± 0.10
Jaegerc
0.92 ± 0.47
1.50 ± 0.31
0.67 ± 0.33
1.03 ± 0.22
0
0.50 ± 0.26
0.50 ± 0.23
0.33 ± 0.15
0.08 ± 0.08
0
0
0.03 ± 0.03
Arctic fox
0
0
0
0
Common Raven
0
0
0
0
Snowy Owl
0
0
0
0
Arctic gr. squirrel
Red fox
a
Early = 6/20 and before, Middle = 6/21 to 7/5, Late = 7/6 and after, Season = all time periods. Total sample size for each period = number of study plots (12).
Total detections: Glaucous Gull (n = 57), Parasitic Jaeger (n = 24), Long-tailed Jaeger (n = 13), Arctic Ground Squirrel (n = 12), and Red fox (n = 1).
c
Combines all jaeger species
b
32
Table 8. Summary of overhead nest concealment for the most common species (n ≥ 10) and
species groups at the Ikpikpuk River study site, National Petroleum Reserve - Alaska, 2010.
Species
n
Mean concealment ± 1 SE
Dunlin
10
18.00 ± 3.27
Lapland Longspur
28
56.61 ± 5.42
Pectoral Sandpiper
23
27.83 ± 3.92
Red Phalarope
15
19.33 ± 3.58
Semipalmated Sandpiper
56
22.14 ± 2.32
Shorebirds
123
21.30 ± 1.50
Passerines
30
59.17 ± 5.36
Phalaropes
19
21.58 ± 3.27
33