ABUNDANCE, HABITAT SELECTION, AND FOOD HABITS

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ABUNDANCE, HABITAT SELECTION, AND FOOD HABITS
ABUNDANCE, HABITAT SELECTION, AND FOOD HABITS
OF GRASSLAND BIRDS IN 3 NON-NATIVE GRASSLANDS
IN NORTHERN ILLINOIS
by
Scott N. Kobal
A Thesis
submitted in partial fulfillment of the
requirements for the degree
MASTER OF SCIENCE
College of Natural Resources
UNIVERSITY OF WISCONSIN
Stevens Point, Wisconsin
August 1990
APPROVED BY THE GRADUATE COMMITTEE OF
Dr. Neil F. P
Committee Cha r.man
Professor of W1ldlife
-~~ad
Dr. Milo I
Professor of Soil Science
Dr. Daniel R. Ludwig
Wildlife Biologist
Forest Preserve District of DuPage County, IL
ii
Abstract
Populations, abundance, habitat selection and food habits of
7 species of grassland birds were examined in 3 types of
perennial non-native grasslands (fescue, mixed grass, grassjforb)
in DuPage County, Illinois during 1986 and 1987.
Discriminate
function analysis indicated that grassland habitat types could be
distinguished by vegetation height, percent forb cover, vertical
density of vegetation and percent bare ground.
Mean values for
all these components were greater (t-test, £<0.05) in the
grass/forb habitat type.
Fescue and mixed grass habitat types
contained greater densities (£<0.05) of Savannah Sparrows
(Passerculus sandwichensis), Grasshopper Sparrows (Ammodramus
savannarum), and Eastern Meadowlarks (Sturnella magna).
Densities of Bobolinks (Dolichonyx oryzivorus) and Red-winged
Blackbirds (Agelaius phoeniceus) were higher (£<0.05) in the
grassjforb fields.
Fescue was the only habitat type in which a
correlation (£<0.05) existed between the number of bird species
and habitat size.
Correlations between the number of individuals
and habitat size existed for Savannah Sparrows, Grasshopper
Sparrows, and Eastern Meadowlarks in fescue; Bobolinks in mixed
grass; and Red-winged Blackbirds in mixed grass and grass/forb.
Of the 7 habitat variables measured, all bird species selected
habitats based on differences in litter depth, vertical density
of vegetation and percent cover of grasses and forbs within
habitats .
Residual cover was found to correlate (£<0.05)
iii
with bird density in spring.
·- the 3-na:OTtat. l:ypes.
Insect composition differed between
lffi.e- Targest nultlber
in the fescue habitat type.
or 1.nsec'Cs ··ca-ptured ·was -
The greatest concentration of insect
orders (Orthoptera, Coleoptera, and Lepidoptera) most often
selected by all bird species was in the grassjforbs habitat type.
All bird species did not select insects in proportion to their
abundance.
All bird species were found to be nonselective in
perching substrates, but each species selected perches within a
definate height range.
iv
ACKNOWLEGEMENTS
Dr. Daniel R. Ludwig provided essential editorial help,
guidance and inspiration in the completion of this project.
Dr. Neil F. Payne, my major professor, provided guidance and
editorial help.
analysis.
Dr. Robert Rogers gave advice on statistical
Funding was provided by the Friends of the Furred
and Feathered of DuPage County, IL, and the Forest Preserve
District of DuPage County, IL.
v
TABLE OF CONTENTS
Abstract. . . . . . . • • • • . . . • • • • • . • • . . . . . . • • • • • • . • • • • • • . . . . • . . . . . iii
ACKN'OWLEDGEMENTS • • • . . . . . • . . . • . . • • . . . . • . . • . • . . . • . . • . • . • • . . . .
v
LIST OF TABLES. . . . . • . . . . . . . . . . . . • • • . . . . . . . . . . . • . . • . • . . . . . . .
ix
LIST OF FIGURES. . • • . . . . . . • . . . . . • . . . . . . . . . . . . . . . . • • . . . . . . . . .
xi
LIST OF APPENDICES. . . . . • . • • • • . . . . . . . . • . . . • . . . • . . . . . . . . . . . . . . xii
ABUNDANCE, HABITAT SELECTION, AND FOOD
HABITS OF GRASSLAND BIRDS IN 3 NON-NATIVE
GRASSLANDS IN NORTHERN ILLINOIS .•.•..•••••.••.•...•.•.•.....
1
INTRODUCTION. • • . • . • . • • • • • . . . . • • • . . . • • . . . • • • • . . . • . . . . . . .
1
STUDY AREA. . • . . • • . • • • • • • • . • • • • . • . . . . • • • . • • • • • . . • • . . . . . .
3
DISTRIBUTION, ABUNDANCE, COMPOSITION AND HABITAT/AREA
RELATIONSHIPS OF GRASSLAND BIRD COMMUNITIES •...•............
6
METHODS. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • •
6
RESULTS • . • • • • • . • • • . . . • • . • • • • • • • • • • • • • . • • • . . • . . • . . . . . . . .
7
Bird Species Distribution and Abundance ..•.•.•....
7
Bird Species and Habitat Area Relationships .••.... 12
DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
STRUCTURAL CHARACTERISTICS OF 3 GRASSLAND HABITAT TYPES
IN NORTHERN ILLINOIS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
METHODS. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • .
16
RESULTS. • • • • • • • • • • • . • • . • • • • • • • • • . • . . • • . . . • • . . • . • • . • . • . .
17
Vegetation Species Composition •••.•..••••••.•..... 17
Structural Characteristics of Vegetation .......... 17
DISCUSSION. . • . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HABITAT SELECTION OF 7 GRASSLAND BIRD SPECIES IN NORTHERN
23
ILLINOIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : 2 ·s
vi
Page
METHODS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • . .
. RESULTS-..-.--.-~ .....
-.---.---....-- -.-
.... -.- ......... .-.--.--- .. -. --. .
Individual Species .•
-
-
... .. ..
.----
-
25
-
. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .
25
Henlsow's Sparrow ••.
25
Grasshopper Sparrow.
26
Eastern Meadowlark. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6
Savannah Sparrow.
27
Dickcissel .••••••
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Red-winged Blackbird.
Bobolink •.
... . . ... . . ... .. . .. . . . .. . . . . . . .
. . . . .. . . . . . . . . . . . . . . . . . . . .
Bird Species Relationships.
DISCUSSION ••.•
27
28
28
32
Individual Species .•
32
Henlsow's Sparrow •..
32
Grasshopper Sparrow.
33
Eastern Meadowlark. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5
Savannah Sparrow.
Dickcissel ••.•..•
38
Red-winged Blackbird.
40
Bobolink.
41
Bird Species Relationships.
43
FOOD HABITS OF 7 GRASSLAND BIRD SPECIES AND INSECT ABUNDANCE
.IN 3 GRASSLAND HABITAT TYPES IN NORTHERN ILLINIOS .•.......... 45
METHODS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • 4 5
RESULTS. • • • • • . • • • . . • . • • . . • • • • • • • . • . . • • . • . • . . . . . . . . . . . . . . 4 6
DISCUSSION.
48
vii
Page
RECOMMENDATIONS FOR GRASSLAND BIRD SPECIES AND GRASSLAND
lil\13][~1\~
~~(;~~~~~-
••••••••••••••••••••••••••••••••••••••••••
50
Habitat Management Options Available . . . . . . . . . . . . . . . . . . . 50
Management for Grassland Birds in DuPage County ......... 52
LITERATURE CITED. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Appendices. . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6
viii
LIST OF TABLES
DISTRIBUTION, ABUNDANCE, COMPOSITION, AND HABITAT/AREA
RELATIONSHIPS OF GRASSLAND BIRD COMMUNITIES.
Table 1.
Calculated mean densities (birdsjha) and
standard deviations (SO) for 7 bird species
within 3 habitat types in northern Illinois,
1986-1987. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Table 2.
Correlation coefficients for habitat area
with the numbe~ of individuals for each
bird species in 3 habitat types in northern
Illinois, 1986-1987 ..•..••••.••••......•.......•. 13
STRUCTURAL CHARACTERISTICS OF 3 GRASSLAND HABITAT TYPES
IN NORTHERN ILLINOIS.
Table 1.
Frequency of occurrence of common plant
species within 1 m2 plots in northern Illinois,
1986. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 2.
Sociability of plant species based on BraunBlanquet sociability scale in northern
Illinois, June-July 1986 .••..•..••••............. 19
Table 3.
Discriminate function (OF) coefficients for
separating the 3 grassland habitat types
(fescue, mixed grasses, grassjforb), in
northern Illinois, 1986 ..••••••••••..••..•.•..... 21
Table 4.
Mean values and standard deviations (SO) for
vegetation characteristics of the 3 habitat
types (fescue, mixed grasses, and grassjforb)
and the fescue and timothy dominated grassjforb
sites in northern Illinois, 1986-1987 ..••..•..... 22
HABITAT SELECTION OF 7 GRASSLAND BIRD SPECIES IN NORTHERN
ILLINOIS.
Table 1.
Habitat characteristics selected by 7 species of
birds in 3 grassland habitat types (fescue,
mixed grasses, and grassjforb) in northern
Illinois, June-July 1986-1987 ••.•••..•••••••..... 29
ix
FOOD HABITS OF 7 GRASSLAND BIRD SPECIES AND INSECT ABUNDANCE
IN 3 GRASSLAND HABITAT TYPES IN NORTHERN ILLINOIS.
Table 1.
Proportion (%) of the sweep net samples
represented by 10 insect orders and the
percentage of the food items brought to
nestlings by each bird species in 3 habitat
types (fescue, mixed grasses, and grass/forb)
in northern Illinois, July 1987 . . . . . . . . . . . . . . . . 47
X
LIST OF FIGURES
------------
-
DISTRIBUTION, ABUNDANCE, COMPOSITION AND HABITAT/AREA
RELATIONSHIPS OF GRASSLAND BIRD COMMUNITIES.
Figure 1.
Figure 2.
Frequency of occurrence of 9 bird species
in 3 grassland habitat types in northern
Illinois, 1986-1987 •.......................
9
Percentage of the bird community
represented by 9 bird species in 3
grassland habitat types in northern
Illinois, 1986-1987 .•••..••.•..•........... 10
HABITAT SELECTION BY 7 GRASSLAND BIRD SPECIES IN NORTHERN
ILLINOIS.
Figure 1.
Relationship between height-density of
residual cover and density of breeding
birds in 3 grassland habitat types
(fescue, mixed grasses, and grass/forb)
in northern Illinois, 1986-1987 ...••....... 30
Figure 2.
Comparative scaling of tpe responses of
7 species of breeding grassland birds to
hal:>itat features in northern Illinois,
1986-1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
xi
LIST OF APPENDICES
Appendix A.
-Field length, year of planting, and area
of 21 transects within 3 habitat types in
northern Illinois, 1986-1987 . . . . . . . . . . . . . . . . . . . 66
Appendix B.
The number of individual birds within each
transect in northern Illinois, 1986-1987 ....... 67
c.
Non-grassland birds seen or heard during
bird surveys in 3 habitat types in
northern Illinois, 1986-1987 . . . . . . . . . . . . . . . . . . . 68
Appendix
Appendix D.
Percentage of the total bird community
represented by 9 bird species in all
grass/forb fields and those dominated by
timothy and fescue in northern Illinois,
1986-1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Appendix E.
Relationship between habitat area and the
number of bird species in 3 grassland
habitat types in northern Illinois, 1986-1987 .. 70
Appendix F.
Relationship between habitat area and the
number of Bobolinks in 3 grassland habitat
types in northern Illinois, 1986-1987 . . . . . . . . . . 71
Appendix G.
Relationship between habitat area and the
number of Eastern Meadowlarks in 3 grassland
habitat types in northern Illinois, 1986-1987 .. 72
Appendix H.
Relationship between habitat area and the
number of Savannah Sparrows in 3 grassland
habitat types in northern Illinois, 1986-1987 .. 73
Appendix I.
Relationship between habitat area and the
number of Grasshopper Sparrows in 3 grassland
habitat types in northern Illinois, 1986-1987 .. 74
Appendix J.
Relationship between habitat area and the
number of Red-winged Blackbirds in 3 grassland
habitat types in northern Illinois, 1986-1987 .. 75
Appendix K.
Plant species within fescue (1), mixed grasses
(2), and grassjforb (3) habitat types in
northern Illinois, 1986-87 . . . . . . . . . . • . . . . . . . . . . 76
Appendix L.
Means, standard deviations, and ranges of
grass heights for 5 grassland habitat types
during spring (March) and summer (June-July)
and around songposts of 7 species of grassland
birds in northern Illinois, 1986-1987 . . . . . . . . . . 77
xii
Appendix M.
Means, standard deviations, and ranges of
forb heights for 5 grassland habitat types
during spring (March) and summeru(June July}
and around songposts of 7 species of grassland
birds in northern Illinois, 1986-1987 .......... 78
Appendix N.
Means, standard deviations, ,and ranges of
height-density for 5 grassland habitat types
during spring (March} and summer (June-July}
and around songposts of 7 species of grassland
birds in northern Illinois, 1986-1987 .......... 79
o.
Means, standard deviations, and ranges of
litter depths for 5 grassland habitat types
during spring (March) and summer (June-July)
and around songposts of 7 species of grassland
birds in northern Illinois, 1986-1987 .......... 80
Appendix P.
Means, standard deviations, and ranges of
grass cover (%) for 5 grassland habitat types
during spring (March) and summer (June-July)
and around songposts of 7 species of grassland
birds in northern Illinois, 1986-1987 .......... 81
Appendix Q.
Means, standard deviations, and ranges of
forb cover (%) for 5 grassland habitat types
during spring (March) and summer (June-July)
and around songposts of 7 species of grassland
birds in northern Illinois, 1986-1987 .......... 82
Appendix R.
Means, standard deviations, and ranges of
bare ground cover (%) for 5 grassland habitat types
during spring {March) and stmmer {June-July}
and around songposts of 7 species of grassland
birds in northern Illinois, 1986-1987 .......... 83
Appendix
Appendix
s.
Appendix T.
Frequency of use of plant species by
grassland birds in fescue (F), mixed grasses
{MG), and grassjforb (GF) during transect
counts May-June 1987 ..•..........•.......•..... 84
Song perch use (percentage), mean perching
height and singing height for 7 grassland
bird species in northern Illinois,
June-July 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix
u.
as
Perch Use by Grassland Birds in Northern
Illinois . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Appendix V.
Management Recommendations for Individual
Bird Species. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 0
xiii
l
INI'ROOOCI'ION
large areas of grassland habitat throughout the United States have
:been lost
to wildlife due to intensive agricultural practices and increased
urbanization.
Populations of passerine birds characteristic of these
grasslands, such as the Bal:x>link (IX>lichonyx o:ryzivorus), Eastern
Meadowlark, (Stumella
~)
, Dickcissel (Spiza americana) , Savannah
Sparrow (Passerculus sandwichensis), Henslow's Sparrow
(.Annrodrarnus
henslowii) and Grasshopper Sparrow (A. savannarum) , have declined 84%-98%
since 1957-1958 in northern and central Illinois (Anonymous 1983).
breedin:J sw:vey data and the
Federal
National Audubon Society Blue List also
reported declines of grassland songbirds (Robbins et al. 1986, Tate 1986) .
'lhe Henslow' s Sparrow is
threa~
as a breeding species in Illinois
(Bowles and '!han 1981) •
OVer 8 .1 million ha of tallgrass prairie once covered 60% of Illinois.
Today <1% of that remains in scattered parcels throughout the state
(Amerson 1970) •
'lhe meadows and hayfields that replaced the native
prairie declined substantially in area due to intensification of row crop
fanning, primarily com and soybeans, since the late 1950's, and the loss
of federal fann assistance programs such as the Soil Bank (Warner 1981).
Hay crops dropped from 1. 2 million ha in 1920 to 404, 000 ha by the mid
1970's, and pastureland decreased by 526,000 ha from 1960 to 1975 (lockhart
1978).
By 1982 only 5% of Illinois croplarrl was planted
to forage grasses
2
ani legumes.
Corn crops increased from 3. 6 to 4. 6 million ha and soybeans
rose from 2.2 to 3--6 million lla--fram_ 1964 to 1982 {U.S. -Department of
Connnerce 1984). As
a result, habitat management of grassland areas
controlled by public and private agencies is becoming increasingly
important to the preservation of grassland birds in Illinois.
Portions of the grassland areas within the Forest Preserve District of
DJPage County, IL, will be considered for recreational acitivities and tree
plantings in the future.
need to be detennined.
'Ihe habitat requirements of grassland songbirds
Ecosystem management plans must be fonnulated
before succession alters the quality of these grassland habitats, or
eliminates them entirely.
Infonnation was gathered during this study to
aid planning and.. management considerations for grassland communities so
that the best grasslands are preseJ::Ved for
no~
birds.
OJ::p:>rtunities to observe birds in native grasslands are scarce
(Jahnsgard and Rickard 1957).
'Ibis is especially true in Illinois where
the associations of native tallgrass prairie used by grassland birds were
IlQt _stygied before the !)rairies were pl<:Med (Birkenholz 1973) •
As a
result, the descriptions of habitats used by grassland birds in Illinois
(e.g. Graber and Graber 1963) have been limited nnstly to pastures and
hayfields, as these are the only remaining extensive grassland habitats in
Illinois.
Many studies have focused on the behavior and social
organization of specific species of grassland birds, but few have examined
species' habitat or area requirements (Weins 1969, Samson 1980, Whitmore
1981, Skinner et al. 1984, Kahl et al. 1985).
'Ihe objectives of this study were to: 1) detennine bird species
diversity relative to 3 grassland habitat types; 2) detennine the
3
relationship between habitat size am bird species diversity am abundance;
3)
detenldne
if
st::ructural
cliff~
exist betwE!en 3 grass!~ habitat
types; 4) detennine specific habitat preferences of 7 species of grassland
birds; am 5) detennine food habits of iniividual bird species am food
aburrlance within 3 grasslam habitat types.
SRJDY AREA
'!his study was coniucted in the Forest Presel:ve District of D.lPage
County, Illinois.
IDeated in northeastern Illinois about 32 km west of
<llicago, am within the Northeastem Morainal Division (Mapes 1979, Neely
am Heister 1987) , D.lPage County is a heavily urbanized county of 857 km2 ·
Since 1960, >24,282 ha, 28% of the county's area, have been converted from
agricultural use.
Presettlement vegetation in the county was 75% tallgrass
prairie am wetlam am 25% small savannas am groves tilnbered by widely
scattered oaks am hickories (I..anpi 1985).
CUrrently, the District has al:>out 8Q94 ha of open space within its
system. Non-native grasslams carprise 3035 ha ( 42%) created by seeding
fonner croplams to perennial grasses.
'lhe District acquired >2833 ha of
agricultural lams since the mid-1960's.
'lhese lams were planted mainly
to meadorrl fescue (Festuca elatior) am ladino clover (Trifolium repens)
before 1979.
From 1980 until the present, fonner agricultural lams were
planted with a seed mixture of t.i.Ioothy (Fhleum pratense) , perennial cye
(I.olium perenne) , am ladino clover.
'lhe conversion cover type was changed
because tinoth.y, cye, am clover are less resistant to successional change
than fescue.
4
'lhree habitat types, fescue, mixed grasses, grass/foro, were selected
-Ior this sbldy ---Oll-i:he basis .-Of-plant species COltpOSition -am--percent
coverage of the dcaninant grass and fom species.
Fescue Fields
Fescue fields consisted mainly of 80-95% coverage of meadow fescue.
other grasses such as Kentucky bluegrass (Poa. pratensis), orchard grass
(Dactvlis glanerata) , quackgrass (Agropyron repens) , SlOOOth brare (Bromus
inennis), reed canary grass
(Rlalaris arundinaceae), and tiioothy were
present in small percentages ( 0-5%) •
canrocm
species of forbs included red clover (Trifolium pratense),
Queen-Anne' s-Iace (Daucus carota) ,
CCIDl10l
milkweed (Asclepias syrica) ,
thistles (Cirsium spp.) , yellow Slf.leet-clover (Melilotus officinalis) ,
goldenrods (Solidago spp.) , c::c:moon sow thistle (So:nchus oleraceus) ,
wild lettuces (Iactuca spp.) , field bimweed (Convolvulus arvensis) , hedge
bimweed
Mixed
(~.
sepium), and darrlelion (Taraxacum officinale).
Grass Fields
Mixed grass fields contained varyirg mixtures
of fescue, timthy,
Kentucky bluegrass, reed canary grass, SlOOOth brane, orchard grass,
quackgrass, and red top (Agrostis alba) •
Fescue and Kentucky bluegrass
were the 2 main grass species in these mixtures.
was So-95%.
Coverage of grasses
'lhe remai.ninq grass species were present in larger percentages
(5-20%) in this habitat type than in the fescue habitat type.
CUtitiOll
forbs included Queen-Anne's-Iace, wild lettuces, CCilm:)n sow
thistle, daisy fleabane (Erigeron amus), field bimweed, hedge bimweed,
darrlel.ion, red clover, white clover (Trifolium repens), yellow hop-clover
(l'~ aqrarium) , alsike clover (T. hybridum) , and lamb's quarters
. Ihi*fes, milloeeds, goldenrcds,
ard $Jhite *rcet-clover {U* atbat also @,
(cnencpCligq alba)
yellcnr $,eet-clover,
Anss/For'lc Fields
Grass/forA fields ontaired rni:<tures
of
fescue, tinnttry, Kenb-lclqf
bruegnass, Leed canar? €Flass, srcottr brore, orctra:d lpass, arxl Erackg:ass.
Fields dcrnin$ed lV Unotny lete chansterized hy a dense overage of
forlcs ard other vegetatior relative to the fields atcnrinatet by fescue.
Half (4) of ttpse fietds odrtairpd predcrninantly stard.s of tirncttry
(24.3-97.1 ba) within .ry*
of ottrer $rass ryecies. Feso.rc vns ttre
dcminant grass
in tne otlrer 4 fields.
ForJcs suctr as
thistles, rniloleecls,
clover, r.rhite clover, alsike clover,
goldenrrcds, sweet clovers, red.
€msl
scnr
ttrj.stte, field
birdweed,
@e birdleed, daiqf fleabane, Arcen:anrets-lae, darrleliqr, wild
lettrres, ard ocmtst ragweed (emrsia artsnisifolia)
galass/foris
fields.
eastern ooBtorrpod
ccvered 25-4ot of
A fery trces ard shnrbs suctr as willcnr (SaXE strp. ) ,
(Egi\E deltoides), anl nnrltiflora
rrcse (Rosa
4!!L][@) ustnlly rcle preserrt, rnainly in r1lEt, dqtgsiqns
fenerurls.
fhese r.ioody qrecies ocrprised <10t
arri a1or.g
of the a:ea of
eactr
field.
6
DIS'IRIEIJI'ION, Ail.JNI:lllliCE, <XMEOSITION, AND HABITAT/AREA RElATIONSHIPS OF
GRA.SSI:AN9--BI CX?M4UNITIES-.
ME'IHOOO
A field was considered 1 samplin:J unit if it consisted of a sin:Jle
habitat type,
am
was
(e.g.fencerow, road).
not visually or !ilysically divided by a barrier
I assigned 21 fields, 8.9-97.1 ha,
types on the basis of plant species CCIIlp)Sition
daninant grass
am foro species.
grasses (8.9-40.5),
(.Apperrlix A).
Dle
to 1 of 3 habitat
am percent coverage of the
Eight fescue (8.9-87 ha), 5 mixed
am 8 grass/foro fields (8.9-97 .1
ha) were sampled
to the excavation of artificial lakes, a fescue am a
mixed grass field, each 40.5 ha, were not sampled in 1987 (Appenjix B).
Bird surveys were comucted 3 times each year, from 28 May-17 June
1986 arrl 21 May-10 June 1987, to detennine the presence of at least 90% of
the breejing birds within the area (Kendeigh 1944).
surveyed on successive days between 0530
Fields usually were
am 1200 hours. SUrveys were not
corrlucted under conditions of poor visibility, fog, steady drizzle,
prolon;Jed rain, or when wims exceed 19 1q:il (U.S. Fish
1972). '!he period between the 1st
am 3rd bird surveys
Fields were surveyed for birds by
alxJut 20
nVmfn.
Wildlif.e SeJ:vice
was always < 7 days.
straight line transects at
Transects were located in the middle of fields to avoid
c::otmtin] birds usin] edge habitat.
distirguishable),
wa1.kinJ
am
am
Bird species, sex (when
the number of individuals per species obser.ved within
60 m on each side of the transect line were recorded (Emlen 1971, 1977,
Mikol 1980).
Birds were identified with 10 x 50 binoculars, or by song.
'!he !ilysiogany of fescue
am tilrothy differs substantially, so the
percent species CCIIlp)Sition of the bird camnunity in each field type was
calculated separately.
7
Olaracteristic grasslam breedirg species -were analyzed because they
were widespread am numerous enough to detennine if a relationship existed
- - - . between the habitat type size ani the aburDance .(rnnnber of i:rtttviduals)
each species.
oru .
'lhese species included the Bobolink, Eastern Meadowlark,
Red-win:1ed Blackbird (Agelaius tpoeniceus) ' Savannah Sparrow' am
Grasshopper Sparrow.
'lhe Dickcissel am Henslow' s Sparrow, found in only a
few areas am in low numbers,
"Were
emitted from the analysis.
'!he
Red-win:1ed Blackbird was included because it was the IOOSt numerous bird
species duri.rg both years of the study am I wanted to see what affect its
presence had on the abun:lance am distribution of true grasslam birds.
RESUI1I'S
Bird Species Distribution am AlJurmnce
'lhe 9 IOOSt c::::cmoon grasslam bird species seen duri.rg the breedirg
seaSon -were the Red-wi.rged Blackbird (1066), Bobolink (246), Savannah
Sparrow (192) , Eastem Meadowlark (155) ,
soD:J Sparrow
~lospiza melodia)
(64), Grasshopper Sparrow (37), Dickcissel (7), Field Sparrow (S,pizella
-plSillg) (4)'
am
Henslew's Spanew (2} (~ B) •
Dickcissels ani
Henslow's Sparrows -were foun:i only in the grassjfort> fields.
Dickcissels
occurred in tiloothy-daninated fields, am Henslow's Sparrows in
fescue-daninated fields.
Field Sparrows -were foun:i within am next to
fescue am mixed grass fields surrourxled by trees am shrubs where it
nested.
I observed 22 non-grasslam bird species (Apperrlix C) •
Fifteen of the
species observed -were characteristic inhabitants of woodlam edge areas,
shrubby areas next to woodlams am fields' ani subw::ba.n areas.
Except for
8
the Northe:m Harrier (Circus cyaneus) , all are conunon breeding species in
Illinois.
-
!
'lhel3obolink, Eastern Meadowlar-x; Savannah
sparrow, Grassnopper
Sparrow, Red-winged Blackbird, am Song Sparrow occurred in all 3 habitat
types (Figure 1) •
'!he Bobolink, Easte:m Meadowlark, am Red-winged
Blackbird, the 3 most ubiquitous grasslam species, occurred in nearly all
fields (90-100%).
Red-winged Blackbirds, Bobolinks, am Easte:m Meadowlarks comprised
65-85% of the bird conununity in all 3 habitat types.
represented
~75%
Two or 3 species
of the total ccmnunity stn.lcture in each habitat type
(Figure 2, Apperxlix D) •
Predominant species were the Savannah Sparrow,
Red-winged Blackbird, am Bobolink in fescue, the Bobolink, Easte:m
Meadowlark, am Red-winged Blackbird in mixed grasses, am the Red-winged
Blackbird am Bobolink in grassjfo:rb.
'!he Dickcissel, Grasshopper Sparrow,
Field Sparrow, Song Sparrow, arrl Henslow's Sparrow each represented <10% of
the bird conununity within any habitat type.
'!he grassjfo:rb habitat contained a higher maan density (£.1<0.05) of
birdsjha (0.62) than either the fescue or mixed grass habitat types (0.40)
(Apperxlix B).
(Table 1).
Mean bird densities (birdsjha) for 7 bird species were low
Most species showed higher maan densities in the habitat types
where they c:::c::mprised the greatest proportions of the bird conununity.
Fescue arrl mixed grass fields contained higher densities (£.1<0.05) of
Savannah Sparrows, Grasshelg)er Sparrows, am Eastern Meadowlarks.
Densities of Bobolinks am Red-winged Blackbird were higher (£.1<0.05) in the
grassjfo:rb habitat type.
I.J:M densities (.:::;0.06 birdsjha) of Dickcissels and
Henslow's Sparrows were fOUI'rl in the grass/fort> habitat type (Table 1) .
.
F 188
R
E
98
uE
98
H
78
{~
c
y
liffiJ FESCUE
GO·
!
0
F
58
0
18
c
c
u
n
"r.
N
c
r.
.MIXEU G~ASS
QGHASS/F1HH
3828
Hl
m··
n
1
2
3
1
5
G
7
'____ll;;j '
0
--I
9
BIRD SPECIES
Figure 1. Frequency of occurrence of 9 bird species in 3 grassland habitat types
in northern Illinois, 1986-1987. !=Bobolink, 2=Eastern Meadowlark, 3=Savannar
Sparrow, 4=Grasshopper Sparrow, S=Dickcissel, 6=Red-winged Blackbird, 7=Song ,
Sparrow, B=Henslow's Sparrow,
and 9=Field Sparrow:
·
I
1.0
P
GO
E
n
c
E
58
H
T
... c
0
G tt
E tt
48
i
DliB FESCU¢
I
• tt I XED ~RASS
u 38
FH
0
I
BGRASS/~ORB
I
T
T y 28
II
E
B
18-
I
R
J)
81
2
3
4
5
G
BIRD SPECIES
7
0
9
Figure 2.
Percentage of the bird community represented by 9 bird species in 3[
grassland habitat types in northern Illinois, 1986-1987. !=Bobolink, 2=Easter\n
Meadowlark, 3= Savannah Sparrow, 4=r.rasshopper Sp&rrow, 5=nickcissel, 6=Red-winged
Blackbird, ?=Song Sparrow, O=Henslow's Sparrow, and 9=Field Sparrow.
i
I-'
0
Table 1. Calculated mean densiities (birdstha) and standard deviations (SO) for 7 bird
species within 3 habitat types !in northern Illinois, 1986 and 1987.
Species
Habitat type
N
Mean
so
Bobolink
Fescue
Mixed grasses
Grass/forbs
Fescue
Timothy
94
48
0.10
0.11
0.15*
0.15
0.13
0.05
0.04
0.08
0.07
0.09
79
33
46
Fescue
Mixed grasses
Grass/forbs
Fescue
Timothy
51
38
27
11
0.07
0.13*
0.06
0.09
0.03
0.02
0.05
0.04
0.03
0.02
savannah
Sparrow
Fescue
Mixed grasses
Grass/forbs
131
15
22
0.14*
0.08
0.05
0.11
0.03
0.06
Grasshopper
Sparrow
Fescue
Mixed grasses
Grass/forbs
24
2
10
0.04*
0.03
0.04
0.02
0.00
0.02
Dickcissel
Grasstforbs
7
0.04
0.02
Hens low's
Sparrow
Grass/forbs
2
0.03
0.00
Red-winged
Blackbird
Fescue
Mixed grasses
Grass/forbs
Fescue
Timothy
0.06
0.11
0.31*
0.19
0.43
0.04
0.05
0.17
0.13
0.11
Eastern
Meadowlark
* Significant at .f=O.OS
(,!.-test~.
66
57
47
280
60
220
1-'
1-'
12
Bird Species and Habitat Area Relationships
Fields contained bird canmuni.ties of 2-7 grassland species.
ftelas naa3-6 grasslan:rbiraS;-mixeagrasses had -2::5,
3-7
(AWerrlix B). Seven bird species
medium size (27. 9-52.6 ha) .
Fescue
ana- gra5sjforbha.d
occurred in grassjforb fields of
Dickcissels and Henslow' s Sparrows were
observed only in grassjforb fields.
'Ihe numbers of grassland bird species were p::>Sitively correlated
(log-log transfonnation) with the size of fescue fields (r-=G.51, £1<0.05)
and the fescue-dominated grassjforb fields (_r-(). 73, £1<0.02) (Appenjix E).
Timothy-dominated grassjforb fields showed a negative correlation and all.
grass/forb fields combined showed no correlation (Appen:lix E) .
'!he East..em
Meadowlark, savannah Sparrow, and Grasshopper Sparrow showed strong
positive correlations between the rnnnber of in:tividuals and habitat area
only in the fescue habitat type.
'Ihe Bobolink showed a p::>Sitive
correlation only in the mixed grasses habitat type. 'Ihe Red-winged
Blackbird exhibited a strong p::>Sitive correlation in the mixed grasses and
grass/forb habitat types (Table 2).
Henslow's Sparrows, Grasshopper
Sparrows, am Dickcissels were obsel:ved only ill fields >16 na.
other bird
species occurred in fields of all sizes (AWerrlix B).
DISCUSSION
'!he stnlcture of the breeding bird canrm.mity in perennial non-native
grasslands in DJPa.ge County, Illinois was similar to those reported for
grasslands by Graber and Graber (1963) in Illinois, Weins (1969) in
Wisconsin, Birkenholz (1973) in Illinois, and Nolin and Ritzenthaler (1987)
in Ohio.
In northern Illinois, Graber and Graber (1963) foun:l pastures
Table 2. Correlation coefficients (£) for habitat area with the number of individuals for each bird species
in 3 habitat types in northern Illinois, 1986 and 1987.
Habitat type
Bird species
Fescue
-r
N
Mixed grasses
p
Grass/forb
.!
N
p
..!:.
N
p
Bobolink
0.47
15
<0.10
0.77
9
<0.01*
0.47
16
<0.10
Eastern
Meadowlark
0.65
14
<0.01*
0.61
9
<0.10
-0.19
15
>0.50
Savannah
Sparrow
0.80
13
<0.001*
-0.03
4
>0.50
-0.40
7
>0.50
Grasshopper
Sparrow
0.79
8
<0.01*
-
-
-
-0.83
5
>0.50
Red-winged
Blackbird
0.17
15
>0.50
0.77
8
<0.02a
0.88
16
* Significant at P=0.05 (t-test).
I-'
<0.001*
w
14
contained species carposition arrl
abl.1njances
similar to those I observed
in the fescue arrl mixed grasses habitat types.
Mixed grass hayfields were
structurany similar to the grassjfort:> habitat type·· ffi my- study.
Graber
-
arrl Graber (1963) found Red.-win;Jed Blackbirds represented 57% of the bird
camnunity, Bobolinks 19%, arrl Eastern Meadowlarks 6%, which corcpares
favorably with 54%, 22%, arrl 7% found in similar habitat for these 3
species in my study.
An inportant characteristic of suitable habitat for Red.-wirged
Blackbirds, which c:omrronly nest in uplarrl habitats (Robertson 1972),
appears to be the presence of dense arrl sturdy Ve:Jetation for nest support.
Several plant species in grassjfo:rb fields, such as dogbane arrl thistle5J
provided such support.
(Zinmennann 1971) •
Dickcissels also prefer habitats with sturdy fo:rbs
Henslow' s Sparrows use grasslarrl Ve:Jetation with
patches of dense herbaceous Ve:Jetation arrl protruding weed stalks (Robins
1971a).
Fescue grasslarrls are generally classified as low edge, low diversity
habitats that generally supply poor habitat to all but a few species of
biLds (Urbanek arrl Klhtstra 1986, Nolin am Ritzenthaler 1987).
rut in my
study, fescue fields arrl fescue-dc:minated grassjfo:rb fields contained
higher densities of several grasslarrl species (Grasshopper Sparrow, Eastern
Meadowlark, arrl Savannah Sparrow) •
Nolin arrl Ritzenthaler ( 1987) considered tiloothy to be
habitat to fescue in Ohio.
far superior
But I fourn tiloothy contained few bird species,
was prone to invasion by fo:rbs arrl shrubs, arrl harbored predominantly
Red.-win;Jed Blackbirds.
Graber arrl Graber (1976) noted that in general the m.nnber of bird
species seen in a given habitat increased as the amount of habitat censused
15
inc:reased.
In Ohio, Nolin am Ritzenthaler (1987) fourrl that the size of
the field was the IOOSt inportant variable in
maintainin:J
large mnnbers of ·
· grassiari:I bird spec-res; with larger fields containing more grasslaiii birifspecies.
I fourrl that only 2 habitats (fescue am fescue-dominated
grass/fort>) showed an increase in number of bird species with an increase
in habitat size, the tiloothy-danina.ted grassjfom fields showed a decrease.
Bird diversity am density are low in grasslams ccmpared to IOOSt
other habitats (Cody 1985).
Grasslam bird cxmm.mities tern to be
daninated by 1 or 2 aburxlant widespread species (Graul 1980).
In my study
each habitat type contained 2 or 3 species that represented >75% of the
bird cxmm.mity.
Grasslams contain relatively haoogeneous vegetation pattems which
lack structural diversity, or patchiness, am limit the number of bird
species that can exploit them (Roth 1976).
Grasslams also contain bird
species with restricted habitat characteristics (Weins am Dyer 1975).
IOOSt
CCI1UlD1
Red-w~
'lhe
species in my study (Bobolinks 1 Eastern Meadowlarks 1 am
Blackbirds) -were observed in fields of all sizes.
n:msities of grasslam btras were generally law i.fi my study.
Graber am Graber (1963) fourn a greater density of birds in mixed
hayfields (grass/fort>) than in pastures (fescue am mixed grass).
Densities fran my study -were substantially lower than those fourrl by Graber
am Graber (1963) in similar habitat.
'lhe lower
~ation
densities might
be due partly to the loss of grasslam habitat in Illinois am resulting
decline in grasslam bird
~ations
am densities (.Arlonyloous 1983).
samson (1980) fourrl that Henslow's
nested only in large grasslams.
Sparrows am Grasshq>per Sparrows
In my study these species were fourrl only
in fields >16 ha, suggesting they may not breed in smaller fields.
16
Sl'RUCIURAL ClJARACI'ERISI'ICS OF 3 GRASSlAND HABITAT TYPES lli
NORIHERN IlLINOIS.
MEil"llOE
Vegetation measurements were taken during the breeding season
(19 June-30 July 1986) and at the tirre of spring arrival of most species of
grassland birds (16-21 March 1987).
Vegetation was sampled within 600
1-m2 quadrats located ran:lanly alon;J bird transect routes (Costing 1958,
Weins 1969, Ohmann and Ream 1971).
of each field (Appendix A) .
Transect lengths varied with the length
A ran:lam numbers table was used to locate 30
quadrats 3-60m on alternate sides of the bird transect line.
'!he plant species, sociability, aburx3ance, height, height density, and
percent cover of grasses and forbs, standing and fallen litter, and bare
grourrl were recorded within each quadrat.
Sociability was detennined by
using the Braun-Blanquet sociablity scale (Mueller-Dambois and Ellenberg
1974).
'lhree representative heights for each plant species were taken
within each quadrat.
'lhree litter depths were taken at the 2 far co:rners
and the center of each quadrat.
Iaubemnire cover classes were used to
estimate percent of grasses and forbs and bare grourrl when present (BarlJour
et al. 1980). All additional plant species obse!:ved within habitat types,
but not occurring within the quadrats, were recorded.
Height-density was recorded as a measure of visual obstJ::uction by
using a pole 1m high with 1-dm sections painted alternately red and white.
A large black number (1-10) was painted on each 1-dm graduation.
was placed in the
center of each quadrat and obse!:ved fran a distance of 4
m and a height of 1 m.
nearest 0.5
'!he pole
'!he lowest number visible was recorded to the
dm (Robel et al. 1970).
17
Discriminate function analysis with stepwise inclusion of variables
(IG.ecka 1975)
was used to detennine the vegetation variables that
statistically separated the
o. 05
3~.
level for all statistical tests.
significance was set
at-~­
'!he statistical Package for the
Social Sciences (SPSS) c:x:mp.rter program was used in the analyses.
'Ihirteen
variables were selected for inclusion in the analysis: number of grass
species, mean grass height, coverage of live grasses, coverage of dead
grasses, total coverage of grasses, mean foro height, coverage of live
fo:rbs, coverage of dead fo:rbs, total coverage of fo:rbs, height density,
litter depth, arxl bare
groom coverage.
RESUI.['S
Vegetation Species Ccmposition
I abseJ:ved 70 herbaceous arxl woody plants (Appen:tix K) .
Fescue fields
averaged 2. a grass arxl 5. 2 foro species, mixed grasses 5. 2 arxl 9. o, and
grassjfo:rbs fields 5.0 arxl 9.6.
Fescue, Kentucky blua:Jz:ass, t.iituthy, an:i srrooth brame were the most
c::aTIOOI1l.y occurrin;J grass species within all habitat types.
occurrirg foro species were canada thistle,
Queen-Anne's-Iace (Table 1).
milkweed
am
I abseJ:ved growth patterns (sociability) of
34 plant species occurrin;J in quadrats.
sin;Jly.
CXll'lll'OC>ll
Commonly
Most (56%} plants obsex:ved grew
Fescue was the only plant species growin;J in large, almost pure
starxls (Table 2) •
structural Characteristics of Vegetation
'!he discriminant analysis i.rrlica.ted that 9 of the habitat variables
separated the 3 habitat types.
'IWo discriminant functions (OF) were
18
Table 1.
plots in
2
of occurrence (%) of common plant species within 1-m
Illinois, 1986. Sample size is given in parentheses.
F~equency
no~thern
Plant species
Fescue
(240)
Mixed
grasses
(150)
Grass/forbs
<240)
Grasses
Fescue
Kentucky bluegrass
Smooth brome
Timothy
Quack grass
Reed canary grass
Orcha~d grass
98.3
3.0
3.0
2.1
1.2
< 1
< 1
83.1
71.3
6.0
5.0
5.0
2.0
2.0
38.7
9.0
15.4
46.7
12.9
4.0
2.9
Forbs
Canada thistle
Common milkweed
Queen·Anne•s-lace
Field bindweed
Common sow thistle
Hedge bindweed
YeltCIW sweet ctover
Red clover
Alsike clover
Goldenrods
11.2
10.8
2.9
2.9
2.5
2.1
< 1
1.2
< 1
1.7
7.3
11.3
5.0
< 1
< 1
4.0
2.0
< 1
< 1
28.7
8.3
4.6
?- 1
< 1
1.4
5.8
7.5
7.9
5.8
< 1
Tabte 2. Sociability of plant ~pecies based on the Braun-Blanquet Sociability Scale
in northern Illinois, June-Jul~ 1986.
a
Plant species
Meadow fescue
Timothy
Kentucky bluegrass
Smooth brome
Reed canary grass
Quackgrass
Redtop
Foxtails
Orchard grass
Canada thistle
Yellow sweet clover
White sweet clover
Red clover
Ladino clover
Yellow hop clover
Goldenrods
curled dock
Sociability rating
5
4
4
2
2
3
4
1
4
4
3
2
Plant species
Evening primrose
Sow thistle
Dandelion
Wild lettuces
Heal-all
Peppermint
Yarrow
Cinquefoils
Dogbane
Bull thistle
Daisy fleabane
Lamb's quarters
Pigweed
Common ragweed
Field bindweed
Hedge bindweed
Queen-Anne•s-Lace
Sociability rating
4
1
3
I-'
1.0
2
3
a
1=growing singly; 2=small but dense clumps; 3=small patches or cushions; 4=small colonies or carpets;
S=large, almost pure stands.
20
derivE:ld by usirq these 9 habitat variables (Table 3).
'!he 1st discriminate
function (DF 1) explained 74% of the variation in the data.
importantnabitat variaBles
5eP8rat~
'!he most
the--fuiliitat types were grass hei(jht,
height density 1 am bare grounj (Table 3) • '!he 2nd discriminate functiOn
(DF 2) explained the additional 26% of the data variation, describirq a
separation between habitat types based on number of grass species am total
cover of grasses.
am
'!he number of grass species present, mean grass height,
total coverage of grasses best discriminated between habitat types, on
the basis of the Wilks' I..anrla values.
Wilks' I..anrla values ? 0.45 were
considered to be significant based on the am::>Unt of separation between the
values.
Mean forb heights, litter depths,
am
percent cover of grasses
fo:rbs were greater (!?<0. 05) durirq sprirq (Table 4) .
am
Grass height, height
density, am percent bare grounj were greater (}?<0.05) in sununer.
r:urirq the b:reedirg season, mean values for grass height, forb height,
percent forb cover, percent bare grounj,
am
height density were greater
(}?<0.05) in the grassjforb habitat type than in the other 2 habitat types
(Table 4).
Percent grass cover
am
litter depth were greater (}?<0.05) in
the fescue habitat type than in the mixed grass or grass/forb habitat types
(Table 4,
~ces
IrR) •
Forl:> cover, height density,
am
bare grounj were greater (}?<0.05) on
the ti.nm:hy-danina.ted grassjforb sites than on fescuEM:laminated sites.
Higher (!?<0. 05) percent grass cover occurred in fescue-dominated
grass/forb fields than on tim:>thy-daninated fields (Table 4).
21
---------------
Table 3. Discriminant function CDF> coefficients for separating
the 3 grassland habitat types (fescue, mixed grasses, and grass/forb),
in northern Illinois, 1986.
Habitat feature
Grass height
Number of grass species
Grass cover
Dead grass cover
Total grass cover
Forb height
-oeaa forb cover
Height density
Bare grOI.nd
•
DF 1
DF 2
0.567
·0.059
·0.358
0.244
-0.326
·0.149
0.044
0.406
0.365
0.225
0.909
0.585
0.346
·0.752
0.004
0.277
-0.04
0.119
sta~ard
Table 4. Mean values and
deviations (SO) for vegetation characteristics of the 3 habitat types (fescue,
and grass/forb) and the fescue~dominated and timothy-dominated grass/forb sites in northern Illinois, 1986-1987.
Grass/forb
-
Mixed grasses
Fttscue
Vegetation variable
so
Mean
so
74.5
94.3*
54.1
11.2
2.1
4.7*
5.2
20.2
5.4
19.2
15.3
0.7
1.3
2.3
74.3
94.7
51.3
12.3
2.2
4.4
4.6
14.1
5.1
20.2
13.6
0.5
1.0
1.7
47.2
92.1
90.6
17.6
1.5
9.3
3.1
14.3
8.7
14.7 .
7.4
0.4
2.1
1.4
48.4
93.4
93.2
20.3
1.7
8.5
2.6
11.2
9.2
13.4
5.2
0.4
1.5
1.3
Mean
Fescue-dominated
Mean
--..
··--·~·~-···~-
~ixed grasses,
....... -~---
Timothy-dominated
ctined
so
Mean
so
Mean
so
14.9
9.4
18.2
14.8
1.3
1.8
2.1
88.1
76.3
58.5
31.3*
3.5*
4.1
19.4*
15.2
17.2
20.6
20.7
1.4
1.9
8.6
91.6*
81.2
59.7*
26.7*
3.3*
4.1
17.1*
15.1
20.6
19.2
24.3
1.3
1.7
10.8
Summer measurements
Grass height (em)
Grass cover %
Forb height (em)
Forb cover %
Height density (dm)
Litter depth (em)
Bare ground %
89.7
92.6*
59.7
15.5
3.2
4.2
5.9
I
Spring measurements
Grass height (em)
Grass cover %
Forb height (em)
Forb cover %
Height density (dm)
Litter depth (em)
Bare ground %
* Significant at E_=0.05 (!_-test').
62.5
86.7
101.2
26.5
2.0
9.2
4.3
10.4
8.8
9.7
8.2
0.5
1.7
1.5
81.2
74.3
109.6
40.3
2.8
3.4
13.4
16.3
7.5
10.1
21.4
0.7
1.2
7.9
64.3
76.7
103.4
34.3
2.3
7.1
11.8
22.6
13.3
16.8
26.4
0.8
4.2
6.7
">
">
23
DISClJSSION
Grasslarrls contain relatively hc:m::XJeneous vegetation patterns which
am· l.i.nUt
laCK:- stru----cfural.-CfiVersicy' or patchiness,
species that can exploit them (Roth 1976).
the rn.nnber
of
bird
Weins (1974) noted a general
reduction in grass cover arrl litter depth arrl an increase in woody
vegetation arrl bare groun:i cover with increases in plot heterogeneity.
In
my study this corrlition was more pronounced in the grass/forb habitat type.
Much of this heterogeneity was attributed to the presence of timothy on the
grass/forb sites.
Timothy was prone to invasion by fo:rbs, particularly
canada thistle, which reduced grass cover.
Height arrl density of vegetation were the factors that
habitat types, arrl which separate grasslarrls in general.
separated~
3
'Ihe different
grass species arrl their grcMth patterns seem to be an important variable
in the physiogany of the habitat types.
'Ihe grcMth patterns of the grass
species present detennine the height of the vegetation, height density, and
the aiOOUnt of bare groun:i, arrl which bird species will be present.
Sociability is an estimate of the dispersion of members of a
plant species, which
aoes
not necessarily have any relationShip to cover.
Several species on my study area had similar cover-abun:3ance, but
distri.buted differently (Bal:i:xJur et al. 1980).
Goldenrod arrl evening
prilnrose had alx:lllt the same cover-abundance, but evening prilnrose was
scattered unifonnily throughout fields whereas goldnerod was restricted to
a few, dense clumps.
Fields in spring corrlition differed from those in summer condition.
Residual cover in spring is subject to overwinter canpaction arrl
fracturing, harvesting by animals, arrl decanposition (Higgins arrl Barker
1982) •
Forbs were taller in spring because only tall, thick-stemmed forbs
24
were present after winter.
SUch fo:rbs provide essential perches for many
species of migrato:ry grasslarxi birds upon arrival.
meaSurements-were lower
crurl:nJ
sprinc~fdue
vegetation occurrirXJ over winter.
Height density
to lodgil'XJ (flattenin;J) of
IDdgil'XJ also resulted in greater litter
depth arxi coverage in spril'XJ.
Whit:nvJre (1979a) fOUI'Xl differences similar to mine in percent cover of
grass, fort:> height, vertical density of grass, arxi height of vegetation
between spril'XJ arrival of grasslarxi birds arxi duril'XJ the breeding season.
25
HABITAT SEIECriON OF 7 GRASSlAND BIRD SPECIES
~--~
m
NORIHERN ILLINOIS
- - ------ ------- ~ --~- ---- MEniOOO
Bird-centered VecJetation samplinJ was c::oniu.cted 15 June-10 July 1987,
between 0530 and 1200 hours.
Territories of Bd:x>links, Eastern
Meadowlarks, Red-winJed Blackbirds, Dickcissels, Grasshopper Sparrows,
savarmah Sparrows, and Henslow' s Sparrows
were located by systematically
traversinJ entire fields durinJ 15-19 June 1987.
:ux:ations of intividuals
or nests were marked with flagginJ tape (larson and Bcx::k 1986) .
Vegetation was sampled at 2 locations aroun:l each songpost or nest.
1-m2 quadrat was placed directly alCDJSide the SCDJPOSt or nest.
quadrat was located 1-10m fran the SCDJPOSt or nest.
A
A 2m
'!he compass
ctirections and distances of the placement of the quadrats were detennined
fran a rarrlcm numbers table.
'!he vegetative characteristics measured were
height density, height and percent oover of grasses and forbs, and stand.in:J
and fallen litter.
Plant species, height of SCDJPOS't, and height of
sinJinJ bird above grourrl were noted.
VecJetation characteristics were measured aroun:l
~
of 142
---------
irrlividual birds.
males were
IOOJ:e
All adult birds were sampled (James 1971) ; but sinJinJ .
cx:mspiruous, and
CX~tprised
>80% of the birds sampled.
RESUiliS
Irrlividual Species
Henslow' s Sparrow
Fescue was the daninant grass in all the sinJinJ areas; SlOOOth brome,
orchard grass, Kentucky bluegrass, and quackgrass also were present.
Habitat aroun:l
~was
characterized by >85% cover of tall grasses
and forbs >80 em (Table 1) and a litter coverage of >8 em without any bare
26
grouni present.
Litter depth was highest (:f<0.05) on territories of
Henslow's Sparrows.
~--~~-
---
~_ _!():ri:Js
within territories of Henslow's Sparrows
-were c:x::llUOOn milkweed, Queen-Anne's-lace, dogbane, sweet clovers, goldenrod,
arxl red clover.
Birds -were ci:>se:l:ved singing fran Queen-Anne's-lace (33%),
white sweet-clover (22%) , dogbane (11%) , nultiflora rose (11%) , arxl orchard
grass (11%) •
Grasshopper Sparrow
Habitat arourrl
~es
of Grasshopper Sparrows consisted of short
to .intennectiate ( 45-80 em) groum vegetation arxl a shallow litter layer
.
(2-5 em) • Another :ilrportant feature was a large percentage (15-25%) of bare
grourxl arourxl SCD]pOSts (Table 1).
Bull thistle (19%),
SON
thistles (13%),
evening primrose ( 13%) , arxl goldenrod ( 6%) -were used as sorg perches.
CUtaton fo:ri:Js in territories of Grasshopper
sparrows
"Were
asters,
goldenrods, c:x::.moon milkweed, evening primrose, thistles (bull,
canada,
ani
SON) , yellow sweet-clover, ani white sweet-clover.
Fastern Mead.owlark
Habitat at singing locations had predaninantly grassy cover (90-100%)
of nv:Jderate mean heights (60-80 em), deep litter depths (4-8 em), arxl no
bare grourxl present (Table 1) •
Grasses fOUI'rl on Fastern Meadowlark
territories included fescue, Kentucky bluegrass, arxl SlOOOth brane.
Grass
coverage on Eastem Mead.owlark territories was greater (:f<0.05) than on
territories of other bird species.
CUnnDn
forl:Js within territories -were
canada thistle, c:x::.moon milkweed, Queen-Anne' s-lace, arxl goldenrods.
Perches used included shrubs (32%) , :mUltiflora rose (14%) , trees (14%) , ani
c:x::.moon milkweed (14%).
27
Savannah Sparrow .
Habitat arourrl 50n3' perches of savannah Sparrows was characterized by
80-98% grassy coVer of m:xierate heights (60-90 em)
am
litter depths (4-6
am percent bare grourrl cover (15-20%) (Table 1). Territories centered
aroum carmon fo:rbs such as canada thistle, evenirg primrose, carmron
milkiNeed, sweet clovers, Queen-Anne' s-lace, goldenrods, am asters. Conunon
~es were multiflora rose (21%), canada thistle (17%), shrubs (13%),
am goldenrod (13%).
em)
Dickcissel
Dickcissels were fOUI'rl in disturt:led areas with developed starrls of
dense, thick-stemmed fo:rbs.
'Ihese areas contained predominantly fo:r'bs
· ( 68%) , with percent cover in sane cases of >90%.
included evenirg primrose, Queen-Anne' s-lace,
aroum
COnuton foro species
am canada
thistle.
Habitat
solX]pEU'Ches was characterized by 50-90% tall ( 60-110 em) fo:rbs,
20-30%. coverage of bare gra.:md, 0.5-4 em litter depths,
vegetation (2-5.5 dm) (Table 1).
am
dense
Foro coverage was greatest (£!<0.05)
am
grass coverage was lowest (£!<0.05) on Dickcissel territories than on those
of other bird
(18%),
am
speci~.
Perches used were shrubs ( 18%) , evenirg primrose
goldenrods (9%) •
Red-winged Blackbird
Habitat arourrl son;rperches of Red-wirqed Blackbirds was characterized
by tall grasses (75-120 em)
dm),
am
am
fo:rbs (65-130 em), dense vegetation (3-5.5
IOOderate aiOOUnts of bare grourrl (12-20%).
Territories contained
28
alnDst equal coverages of grasses am fo:rbs (Table 1) •
WQnl
~T
dQgbane
fU%t-, trees
(12%)
1
Songperches used
am burdoch (12%) •
Bobolink
Although Bobolinks were a1::1l.mlant, relatively few vegetation samples
were taken.
By the time vegetation sampling had begun (15 June) , Bobolinks
had fledged am family units had assembled into small highly m::>bile flocks.
Males were molting am no longer deferrling territories.
Bobolink
territories were characterized by large anx>Ul'lts (75-95%) of tall (70-100
em) grassy cover, deep litter depths (3-7 em), am no bare grourrl (Table
1) •
~es
c::c:mtal
used included goldenrod ( 43%) , multiflora rose (21%) , and
milkweed (14%).
Bird Species Relationships
Residual vegetation in spring was J:X>Sitively correlated (.r-G.44,
E<O.OS} with breeding bird density in May-June (Figure 1).
'!he breeding
grasslam birds could be arrarged on the basis of increasing vegetation
height am density am litter depth of the habitats they occupied in the
follc::JWirg sequence: Grasshopper Sparrow, Eastern Meadowlark, Savannah
Sparrow, Bobolink, Henslow' s Sparrow, Dickcissel, Red-winged Blackbird
(Figure 2).
Savannah Sparrows, Eastern Meadowlarks, am Grasshopper
Sparrows had overlawing nidles. So did Bobolinks am Henslow's Sparrows.
30
~
.+J
.....
en
s::Q)
1
'0
I
.+J
..c
IJ.S
.....0\
.
.
. ·.- .r
Q1
::t:
IJ
IJ
_Figure 1.
IJ.Z
IJ.1
IJ.&
I ii"Cl clen8 i t.y C"b ii"Clss'h& l
a.a
1
Relationship between height-density of residual
cover and density of breeding birds in 3 grassland habitat
types (fescue, mixed grasses, and grass/forb) in northern
Illinois, 1986-1987.
oat
II
Gross height (em). ·
0
~5
0
r-- - - -
0
~5
r: lA
Forb cover (%)
I
!I II
11!1 9
0
0
I
9 ,lUI
Bore ground ('1!.)
0
~
,r: M
n W !HI
II
I
to'lft
Figure 2.
76
"
1
601ft
nw
one
I 00 em
,--751ft
L,
i"i
r
I
IOO'Ift
rT
w
I
2.5
r "f ltf' '"'I
~
o
1111
.
I
Tr
I
100" '
I LI.. _____L __,
nr
~61ft
llelyhl --densll y (lim)
I1
60 em
I I I I ,I
"~
.1 .lllf!lll
11'_____1
Ott
"
__j I
!t
100 ~ml
761ft
o" "I'
_j
em
(1
1
78 am
601ft
""'I
Forb heiyhl (em)
n
I
I
~51ft
0
•r 'll';
·J
RW
I
T
Utter detJih (em)
80 am
em
Gross cover (%)
1
@M
6
11!1
8
I~
L___
r=M
6
10
8
r
f
60"
116 ,.
Comparative scaling of the responses of 7 species of breeding
grassland birds to habitat features in northern Illinois, 1986-1987.
HS=Henslow's Sparrow, GS=Grasshopper Sparrow, EM=Eastern Meadowlark,
SH=Savannah Sparrow, D=Dickcissel, RW=Red-winged Blackbird, and
•
B=Bobolink~
1-'
32
DISCIJSSION
In:iividual Species
Henslow' s Sparrow
Few published quanitative data on habitat exist for Henslow' s Sparrow.
Robins (1971a,b) described its habitat as grasslarrl with patches of dense
h.el:baceous vegetation arrl protruding dead weed stalks on sites that are
intennediate in m::>isture ra.n;Je.
Henslow's Sparrows are fourrl in tall,
dense vegetation (Hyde 1939, Graber 1968, Weins 1969, Robins 1971a) .
et al. (1985) fourrl grouni vegetative height was typically
tall on occupied areas.
Kahl
0.20-0.40 m
Areas with grass heights >0.50 m were avoided.
Birkenholz (1973) founj them ITOst abun:.:1ant in areas 'Where the grassy cover
was dense arrl > 62 em, arrl they were absent in areas 'Where taller grasses
predaninated.
In my study the few Henslow' s Sparrows observed occupied
areas with a mean grass height of 84 em.
I.lldwig (pers. cannn.) found
Henslow' s Sparrows absent on native tallgrass prairie in D.lPage County.
Although Henslow' s Sparrows prefer tall grass cover, they are absent in
areas of extremely tall grass (Birkenholz 1973).
Vegetation density is .i.np:>rtant in areas inhabited by this sparrow.
In Missouri, Kahl et al. (1985) fourrl the species usirq areas with >95%
grourxi vegetative cover.
Weins (1969) fourrl vegetation density the most
distinctive feature in its habitat.
In my study, Henslow's Sparrows
occupied areas with no bare grouni present arrl dense, tall (mean 3.3 dm)
vegetation.
Litter is .i.np:>rtant to Henlsow's Spa:rrow.
Robins (1971a) noted it as
a major habitat requirement, arrl Kahl et al. (1985) founj litter coverage
>95% optimum.
Birds avoided areas with <60% cover.
Weins (1969) noted
33
greater litter depth, coverage, arrl
c:atpactness
on territories of Henslow's
Sparrows--than -01'1--tilose of ~-grasslam speeies in- WiseeHSin.---Utterdepths (>8 an) arrl cover (100%) in my study agree with Weins (1969) arrl
Kahl et al. ( 1985) •
Grasshopper Sparrow
'Ihroughout the U.S.
Grasshower
Sparrows inhabit a wide variety of
grasslarrl situations lacking dense or tall woody vegetation, including
prairies, hayfields, arrl old fields (Smith 1963, 1968, DeGraaf et al.
1980) •
Grassh~
Sparrows are carm::>n breeding birds in suitable short
.
to middle height grasslarrl throughout mudl of North America (WhitJnore
1979b, 1981). In Missouri, birds preferred areas with hert:aceous vegetation
2-3 dm tall arrl avoided areas <4 dm (Kahl et al. 1985).
In West Virginia,
WhitJnore (1981) fOUI'Xi the mean vegetation height was 43.8 an.
Cody (1968)
fOUI'Xi vegetation was 0.31-0.36 m tall on several grasslarrls inhabited by
Grasshopper Sparrows.
WhitJnore arrl Hall (1978) fOUI'Xi
Grassh~
Sparrows
preferred areas of tall grass (about 1 m) on reclaimed surface mines in
West Virginia.
Graber arrl Graber ( i963) fourrl Grassh~ Sparrows to be
the only grasslarxi bird species that preferred alfalfa fields in Illinois.
Alfalfa fields had low vegetation 30-60 an high
am
were fairly open.
Vegetation heights ( 45-80 an) in my study seem higher than in previous
studies.
'!he J;ilysiogany of grasses is iltp:>rtant to the Grasshopper Sparrow.
Grassh~ Sparrows
often forage in open, unvegetated areas (Weins 1973) .
Nest placement ocx:urs in open areas of bunchgrass (Weins 1973, WhitJnore
1981) in low to medium cover (Skinner
et al. 1984).
Smith (1963, 1968)
often fOUI'Xi Grasshopper Sparrows only in areas of bunchgrasses, sudl as
34
orc::hard grass
am.
bunches of fo:rbs such as red clover.
~-Sparrows
(fescue
am.
In my study,
were feurxl---aln\est;-exehlsively in-areas of bunchgrasses
tinDthy).
Whitloc>re (1981) fourxi Grasshopper Sparrows preferred bunch.grasses to
sodfo:nners because the dense ma.t of vegetation produced by sodfo:nners
precluded effective foragirg.
am.
Bunchgrasses terrl to produce more open areas
bare grourrl than sodfo:nners.
Bare grourrl is aburrlant on territories of GrasshQR:)er Sparrows (21. 9%,
Whitloc>re 1981; 22.9%, Bcdc
am.
Webb 1984; 24%, Whitloc>re 1979a).
I observe:i
similar percentages (21%) of bare grourrl.
Vegetation density usually varies in areas occupied by Grasshopper
Sparrows.
DeGraaf et al. (1980) fourxi GrasshQR:)er Sparrows used uplanis of
continuous tall, herl:>aceous grourrl vegetation of various densities.
Whitloc>re (1981) noted that territories -were more sparsely vegetate:i than
non-territories.
Whitloc>re
am
Hall (1978) fourxi GrasshQR:)er Sparrows
deferrli.n;J territories in areas of denser grass than either the savannah
Span'clrl or Eastezn Meadowlark.
In Mi.SSGUri, Kahl
et al. (1985) noted that-
birds ma.intained territories in areas of dense grourrl cover of <85%
avoided areas of less grourrl cover.
am
In my study GrasshQR:)er Sparrows
occupied areas of sparse, open vegetation (21% mean bare grourrl cover, 1.8
dm mean height density).
Litter depth selected by this species was low in my
am.
other studies.
Whitloc>re (1981) note:i a mean litter depth of 2.4 em on territories in West
Virginia.
Weins (1973) fourxi litter depth was 1.2 em on areas occupied by
GrasshQR:)er Sparrows,
am more
on unoccupied areas.
Kah1 et al. (1985)
fOl.lni GrasshQR:)er Sparrows occupied areas of intennediate litter
accumulation (0.1-2 em).
35
Grasshopper Sparrows generally avoid areas of encroaching woody
--
~on-,
:ru-t- use- areas with-a few lOVl woody--sterns- for perches.
Missouri, habitat
aroum
song perches consistantly lacked woody stems and
the birds were absent where woody plants <1 m tall invaded
1985).
In
(Kah.l et al.
Whitlro:re (1981) fourrl mean shrub cover of 0. 7% on territories in
West Virginia.
In Arizona, occupied areas had a mean shrub canopy of 4.5%
(Bock and Webb 1984) •
Johnston and Ochnn (1956) fourrl Grasshopper Sparrows
on early successional plots with <10% shrub cover.
Eastern MeadCMlark
'!he Eastern MeadCMlark was 1 of the IOOSt widespread species obseJ:ved
It is fourrl mainly in grasslands, meadows, and pastures
during my study.
(Bent 1958).
It was the IOOSt abunjant bird species in Illinois in 1909,
and was still abundant in 1956-58 (Graber and Graber 1963).
Lanyon (1956)
and Weins (1969) fourrl it in large, grassy fields with elevated singing
perches and sane litter.
Eastern- MeadCMlarks prefer areas of lCM to medium height grass cover. In Wisconsin,
Weins (1969) fourrl birds selected areas with 70% grass
coverage at the time of their spring arrival. Sdlroeder and Sousa (1982)
fourrl qlti.mum c:xntitons in areas with >80% he:r:baceous cover in grass.
Areas with <20% grass cover are unsuitable.
dense vegetation.
canopy coverage.
Eastern MeadCMlarks choose
Optimal he:r:baceous vegetation densities occur at >90%
Areas with a canopy coverage of <20% are not suitable
(Sdlroeder and Sousa 1982).
In Missouri, Kah.l et al. (1985) found the
optimum range for Eastern Meadowlarks included dense grourrl vegetation with
>95% coverage.
'!hey avoided areas with <70% coverage.
Eastern Meadowlarks in these qlti.mum c:xntitons.
I fourrl :rrost
36
Grass height selected is fairly short.
fora.gi.rg
ard-1~ -aN 1-Q..--30 Glh
Ideal vegetative heights for
PEme--flabitats had a-spring-season
canopy height 12.5-35 em, with 25-50 em the best heights for nesting
(Roseberry arrl Klimstra 1970).
Areas with cover <2.5 em or >76 em were not
suitable (Schroeder arrl Sousa 1982).
Heights within areas occupied by
Eastern Meadowlarks in my study fell within the ranges outlined by
Sdlroeder arrl Sousa ( 1982) .
Eastern Meadowlarks generally occupy territories containing litter.
Females use the dense grourrl cover arrl sare litter for nesting (Bent 1958,
Harrison 1975, DeGraaf et al. 1980).
Kahl. et al. (1985) fourrl Eastern
Meadowlarks occupied areas of intermediate to dense litter coverage (>65%)
arrl avoided areas with <40% coverage in Missouri.
In Illinois, Roseberry
arrl Klimstra (1970) fourrl the presence of dead grass stems at grourx:l level
a primal:y requirement for nesting.
Beec:her ( 1942) noted that nests of
Eastern Meadowlarks are always in the dey growth of the preceeding year.
Ianyon (1957) fourrl nests in Wisconsin always placed in clumps of litter or
_ unier dense overllarging grasses.
Weins {1969) foun:i Eastern Meadowlarks
selected areas with a mean litter depth of 2.5 em, upon their arrival in
Wisconsin.
In my study, Eastern Meadowlarks occupied areas with a mean
litter depth of 5.8 em during the breeding season.
'!he presence of large ai1'Dlli1ts of woody vegetation generally has a
negative affect on the Eastern Meadowlark.
Optimal habitat for them
contains <5% shrub canopy; areas with >35% shrub cover are usually
unoccupied (Johnston arrl Odtnn 1956, SChroeder arrl Sousa 1982).
Roseberry
arrl Klimstra (1970) noted no woody vegetation in the innnediate vicinity of
nest sites in Illinois.
In Arkansas, Shugart arrl James (1973) rarely found
37
Eastern Meadowlarks in grasslams with greater than 17% canopy closure.
Eastern -Meadowlcn-ks ~ied~ -ef---<10%--shrub -eever during my-study;-
Savannah Sparrow
'!he Savannah Sparrow's breeding ran;}e exterm over northern North
America in tallgrass prairies, weedy fields arxi edges, swanps, tumras, and
cx>asta1 marshes (Baird 1968, Welsh 1975, Dixon 1978, Cody 1985) .
'!heir
habitat requirements in Wisconsin conprised open, noist, low lying, grassy
fields with scattered fort:ls arxi fairly dense grourxi VE!g'etation (Weins
1969).
Savannah Sparrows occupy a wide ran;Je of grasslarxi types but prefer
grasses arxi other herbaceous vegetation of nn:lerate heights (Skinner et al.
1984, DeGraff arxi Rudis 1986) •
In West Virginia, upon arrival they
generally chose sites with grass 25 em high; during the breeding season,
heights averaged 65 em (Whitm:>re 1979a). VE!g'etation during the breeding
season in my study was 60-90 em high.
Vegetation is usually dense in territories of 5avannah Sparrows (Weins
1969, Kanb:ud arxi Kologiski 1982) •
But when cover becanes too dense the
number of Savannah Sparrows, am Grasshower Sparrows,
al. 1982) •
declines (Wray et
In my study, Savannah Sparrows· chose areas of intennediate
height density (2.5 dm).
Savannah Sparrows require sane bare grourrl.
Bare grourxi coverage was
15-35% when they arrived in spring (Weins 1969, Whitm:>re 1979a) •
Savarmah
Sparrows usually forage on open grourrl arouni the perimeter of grass
cl\llll)S, but avoid dense VE!g'etation stams (Weins 1969, 1973, Bedard and
LaPointe 1984).
other studies.
My values (16.2%) for bare grourrl concur with those from
38
Tester arxi Marshall (1961) fc:JUM a positive association between the
- - - - unnmber of Savannah Sparrc7.Ns ani litt:er cover, concluding that they need ~
yr. aocumul.ation of litter after a fire.
Weins (1969) fc:JUM that they
selected areas with a mean litter depth of 3.1 em upon arrival in sprinJ.
Whitm:>re (1979a) fc:JUM Savannah Sparrows selected areas with 1.3 em of
litter upon arrival in early sprinJ arxi 1.08 em at the peak of the breedin]
season.
Mean litter depth was higher in my study (4.5 em).
Weins (1969)
fc:JUM that nests were placed in hunmx:ks of litter an:i that litter in
l'lE!Stin:j areas was deeper than in other locations oocupied. Potter (1974)
noted nests in Michigan were placed in tents or mats of dead bluegrass.
Woody vegetation is
habitat.
nat a desirable aspect of Savannah Sparrows'
Weins (1969) noted that fields with shrubs or small trees were
uninhabited by Savannah Sparrows.
Smith (1963) fc:JUM that Savannah
Sparrc7.Ns were able to maintain their population density better than
Grassh<:gler Sparrows could in fields with
i.nvadin:J
shrubs.
Maher (1979)
fc:JUM that Savannah Sparrows require scattered patches of low shrub oover
tor
perc:h.es.
When .'WQQdy vegetation invaded fields in West Virginia,
Savannah Sparrows arxi Grassl'l<:.'g)e Sparrows declined arxi Field Sparrows
~tically
increased (Wray et al. 1982).
Di~issel
Dickcissels are dlaractersitic of disturtJed (subseral) arxi
agricultural habitats (Kemeigh 1941), alt.halgh the highest densities are
recorded fran prairie areas.
'!hey are usually absent fran true grasslarxi
c:cmmmities except in certain years (COdy 1966).
noted that
Graber arxi Graber (1963)
they oocupied a variety of habitats throughout Illinois.
39
Height am density of hamceous vegetation are important aspects of
the Dickcissel's_babitat.
'!he~
of terr-itorial- males is-depeHEient.
up::>n the volume of vegetation (Zinnnennan 1966, 1971) •
Grasses and fort>S
were generally taller in primary habitat (oldfields) than in secondary
habitat (true prairie) (Zinnnennan 1984 I Zinnnennan am Finck 1985) • Taller
am
denser vegetation resulted in lower predation
nestirg birds (Z.i.mmennan 1983).
territories of
m:>:nogam::>US
am
parasitism rates on
Ground vegetation was also taller on
am polyganous males
than those of unmated males.
'Ihe mean height of vegetation was 0. 5-1. 2 m within territories of
successsful males (Z.i.mmennan 1966, Hannenson 1974).
In Missouri, ground
vegetation on average was >0.20 m high for IOOSt sorg perch plots, but
typically <0.60 m (Kahl et al. 1985).
Dickcissels generally were attracted
to fields with dense, low vegetation. Fields of clover, alfalfa,
tiloothy are preferred (Gross 1921, Hurley am Franks 1976).
am
Habitat around
sorg perches was characterized consistantly by dense ground vegetation
(>95% coverage).
1985}.
Areas with <85% ground cover were avoided (Kahl et al.
My values (62.5 gn ani 3.8 dm) for vegetation heights
am
densities
concur with other studies.
Forts are an important oooqx>nent of the habitat of the Dickcissel.
Oldfields are generally preferred over other habitats due to the
heterogeneity of vegetation am the greater fort> coverage (Zimmennan 1982).
Olclfields examined by Zimmennan (1971) had fort> cover of 33-43%.
important as perches (Bent 1958)
1963, IDrg
am nest
Forbs are
sites (OVenni:re 1962, Meanley
et al. 1965, Harrison 1975).
Although Dickcissels sin} re:JU].arly fran low woody vegetation
...
(Zimmennan 1966, 1971, Kahl et al. 1985), abun1ant woody vegetation is
umesirable habitat.
Shugart and Jarres (1973) fourxi Dickcissels nainly on
40
recently clisturt>ed grasslams with few woody stems 1.2-1.5 m tall.
~
Habitat
in--Missotlri -was characterized by-few or no--woodyst:errs
>2.5 em dbh am no woody stems <2.5 em dbh (Kahl et al. 1985).
Zinunerman
(1966, 1971) fOlll'Xi that male Dickcissels were not responsive to the height
am density of woody vegetation, but chose :p:>rtions of the habitat
containing proportionally larger patches of grasses am forbs. Density of
woody vegetation on average was <1%, am present in many territories.
Woody
vegetation is at times used for nest placement (Harrison 1975).
Red-winged Blackbird
'!he Red-wirged Blackbird is an al::luOOant am adaptable species.
Few
species of birds mx:lerwent such a dramatic increase in Illinois since the
turn of the centw::y (Graber am Graber 1963).
Traditionally considered a
wetlam nestirg species, the Rsdwirg has adapted to habitat changes irrluced
by hmnans.
'!hey
r'Dil
c::c:moonly nest in hayfields, alonq roadsides am
ditches, am in other uplam habitats (Dolbeer 1976).
In 1909, 60% of
_ Red---winqed Bl-ackbirds in Illinois were f-eun:i in l'tliH'Sh habitat; by 1958 only
3% were in marshes (Graber am Graber 1963) •
While
Reclwin3s
c::cmoonly nest in marshes am in uplams in habitats
suitable for meadowlarks am Bobolinks, population density is lower in
uplams (case am Hewitt 1963).
tall, dense cover.
Red-wirged Blackbirds generally prefer
Breed:irg birds are attracted to tall vegetation that
restricts visibility (Albeers 1978).
Habitat arourxi sorxwerches was most
conistantly characterized by tall groun;i vegetation ( 4-9 dm) ; areas <4 dm
were avoided (Kahl et al. 1985) •
'!he presence of vegetation that restricts
visibility was 100re inp:>rtant than the mnnber of plant stems am leaves per
41
unit area (Short 1985).
:Red-w.in]ed Blackbirds in my study chose tall,
dense vSJet.ation uin all---habit:at--'types-.-
Fo:rbs, particularly tall, thick-stenuned species, are important for
:Red-w.in]ed Blackbirds.
Numberous species of fo:rbs are used extensively by
Redwi.rgs for nest placement (Stowers et al. 1968, Brown arxl Goertz 1978).
Old growth stems generally are used early in the nest.in] season before new
growth is available (Short 1985).
Woody vegetation was tolerated by Redwings more than by any other
grasslarxl species examined in my study.
:Red-w.in]ed Blackbirds exhibit a
general preference for trees arxl large ano.mts of edge, with trees >5 m
included in IrOSt territories (Albeers 1978).
Areas arouni so~ perches in
Missouri were characterized by low to intennediate rnnnbers of woody stems
>2.5 em dJ::n (24-2100jha) arxl a low canopy (4-8 m, never >8) (Kahl et al.
1985).
Redwings use trees near their breedi.rg territories as observation
posts (Short 1985), arxl forage for insects in the l.Ulderstory, midstory, and
overstory canopies (Robertson 1972, 1973) •
Bobolink
Although Bobolinks are al::m'rlant throughout North AIErica, little
quantitative data exist on habitat comitions.
Weins (1969) stated that
throughout its ~e, Bobolinks are characteristic of large, open fields in
which the grass arxl foro cover is lush.
moist.
Often such habitats are low arxl
Bobolinks are fourrl mainly in northern Illinois, arxl prefer to nest
in mixed grass hayfields arxl pastures (Graber arxl Graber 1963).
Bobolinks generally prefer fields with tall, rank cover on moist sites
(Kantrud 1982, DeGraff arxl Rudis 1986).
foraged mainly in taller grasses.
Weins (1969) fourrl that Bobolinks
Although preferr.in] tall grasses, they
42
are absent where grasses are too tall.
On Goose Lake Prairie Nature
P.resel::Ye in__c:ent.ra1. Illinois, Bci:lol.inks ~ absent-f£an-the native--
tallgrass sites an:l fOUl'Xi only on stands of bluegrass next to the preseJ::Ve
(Birkenholz 1973).
Indwig (pers. cc:mn) fOUl'Xi Bobolinks scarce on areas of
native tallgrass vegetation within OJPa.ge County.
Bent (1958) noted that
Bobolinks preferred nest in cultivated grasslan:ls an:l clover fields than on
the virgin prairie. Preferred hayfields in Illinois have tall (60-75 an),
dense cover with mixtures of grasses an:l legumes (Graber an:l Graber 1963).
Bobolinks often fini optimum corxlitions in rresic meadows with dense
coverage of sedges (carex s;w.) am high foro cover (Beecher 1942,
Wittenberger 1976, 1980).
Weins (1969) placed the Bobolink along with the
Henslow's Sparrow regarding richness of the grasslan:ls it used, an:l
irxlicated that the Bobolink requires tall, dense cover.
In my study,
Bobolinks used tall, dense cover similar in structure to that in other
firrlings.
Litter is 1 of the few habitat features that apparantly is required by
_ thej3obolink.
Tester ani Marshall (1961)
suggested that the depth of
litter was the IOOSt .i.np:>rtant vegetation characteristic which can be
related to density of Bobolinks.
intennediate litter depth.
'!hey fOUl'Xi Bobolinks required an
Bobolinks did not occupy recently bun1ed sample
plots an:l plots with very deep litter.
Johnson an:l Temple (1986) foun:l the
probability of occurrence of a Bobolink nest was higher in sample plots
with 1 growing season since the vegetation was last bunled.
Many Bobolinks
occurred on a restored prairie in Iowa with 5-8 an of dense litter
(Ken:ieigh 1941) •
Litter is .i.np:>rtant for Bobolinks for nesting.
In Wisconsin, Weins
(1969) noted that nests were on the grourrl at the bases of dense grass or
43
foro clunp;.
Joyner (1978) fourx:l that Bobolinks used residual grass an:i
forl::!S for_nest construction arrl_for r:over. --New growths--Of-vegetation-Were
used mainly for perch sites an:i, later, as a source of lepidopteran larvae
for nestlings.
In
my
study, Bobolinks selected areas with deep (>5 ern)
litter, which seemed iJ:tp)rtant as a substrate for nesting.
Foms are iJ:tp)rtant to Bobolinks as perches
am as a source of food.
High quality territories of polygam:us males contained a higher average
percent cover of several foro species than those of umoated males (Martin
1971, 1974, Wittenberger 1976, 1978, 1980).
High foro densities on
favorable territories accounted for higher food availability (lepidopteran
larave) an:l production of young birds.
coverage
am density
Weins (1969) fourx:l that fort>
were similar in occupied
am unoccupied areas, but
mean foro height was greater in occupied areas.
stennned foms were iJ:tp)rtant for singing
Heavy stennned
am lookout
perches.
~ in large percentages on Bobolink territories
am medium
Foms
(>20%) an:l seemed
iJ:tp)rtant for perches an:l a source of insect food for nestlings.
Bird Species Relationships
Weins (1969) noted that habitats of breeding species of grasslan:l
birds differed IOOSt clearly in the density
am height of vegetation. He
also fOlll'Xl groun:l litter an:l forl:> density to be awarant differences.
also observed these differences.
I
'Ihe species richness of habitats of
breeding grasslan:l birds in
my
Weins ( 1969) in Wisconsin.
'Ihe similar habitats of the Savannah Sparrow,
Grasshopper Sparrow,
study were similar to those observed by
am Eastern Meadowlark
were evident in
my study.
Beecher (1942) noted similarities in the habitats of the Bobolnks an:l
Henslow' s Sparrows in Illinois.
44
No data are available on density of
breedi.n:J grasslam son;Jbirds
rela'tive---'te- increasing-~residual--vegetation, although th±s--cozrelation-
exists with nestin;J waterfowl.
Kirsh et al. (1978) reported a direct
relationship between increasin;J duck nest densities am success of
clutches, am increasin;J visual abstru.ction of residual vegetation.
45
FOOD HABI'IS OF 7 GRASSlAND BIRD SPECIES AND INSECI' AHJNDMKE IN 3 GRASSlAND
Food items brought to nestlings were detennined by IIK>nitoring nest
sites 13-22 July 1987 between 0530 arrl 1200 hours with a 15-45X spotting
scope.
I obsel:ved each bird 20 min, arrl recorded all insect food items
presented to nestlings.
Bobolinks, 10
I observed 4 Henslow' s Sparrows, 6 Dickcissels, 7
Grassh.~
Sparrows, 16 savannah Sparrows, 18 Red-winged
Blackbirds, arrl 22 Eastern Meadowlarks fran
~20
m to reduce
obsel:ver-related
ciistw:ba.nces.
.
.
'!he canposition arrl aburrlance of insects within habitat types was
detennined by sweep netting (Menhinick 1963) within fields representative
of each of the 3 habitat types on 23 arrl 24 July 1987 .. Five sanpling
locations were selected alorg each of 4 bird census transect routes.
'!he
4th route was taken within a grassjfort> field in which ti.Ioothy was the
daninant grass species.
'!he different };ilysiogany of ti.Ioothy arrl fescue
might affect insect species eempos-i"tion arrl aburrlance.
SWeep transects
were located at right argles to bird census transects.
Ten steps were
taken alorq each 20-m sweep line.
'lhe vegetation was swept in front of
each step, arrl a 2n:i sweep was made after each step.
made fran right to left 50 en ahead of the collector.
'!he 1st sweep was
A 2n:i sweep was made
fran left to right about 30-35 en ahead of the 1st sweep.
'lhe vegetation was swept vigorously by keeping a stan:iard. 38-cn net as
close to the groun:i as possible (Menhinick 1963) •
SWeeps were made from
the tops of the vegetation to the soil surface, to sanple insects from the
entire strata.
Each sweep covered a horizontal distance of 100-115 en.
'!his procedure continued for 10 steps arrl 20 sweeps (pers. ccmn. R.C.
46
An:lerson, Univ. Ill.) •
~
etl'lanol
Insects fran each sweep line were placed in 70%
ident.ificatien lat;er.
RESUlli'S
'!he 3 IOOSt c:x::llU'OC)n orders (g<O. 05) fed to nestlings, in decreasing
am
order of abun:lance, were Orthoptera, Coleoptera,
Lepidoptera (Table 1) .
All 7 bird species fed their nestlings greater proportions (F<O. 05) of
Lepidoptera
Sparrows
am
am
Orthoptera than available in the fields.
Grasshopper
Savarmah Sparrows fed nestlings greater proportions (F<O. 05)
of Coleoptera than available.
Savarmah Sparrows
am
Eastem Meadowlarks
used Hcmq>tera in lower proportions (g<O. 05) than available.
Sparrows used Diptera in lower proportions relative
(F<0.05) (Table 1).
were large (>10 nun)
am
relatively
am
easy to
catch.
Dipterans (flies) represented 70% of the
insects captured in the fescue habitat type
am
to availability
In general all bird species selected prey items that
Harqrt:erans (leafhoppers)
Diptera
Savarmah
am
59% in mixed grasses.
Coleoptera canprised 58% of the sarrple in the fescue-dominated
grassjforl:> fields ani 48% in the tinDt:hy--dc:.mi..nated fields ('!'able 1} .
Orthoptera, Coleoptera,
~
am
Lepidoptera represented 70-90% of the
fed to nestlings, but only 27% of the insects captured by sweep net
in all 3 habitat types.
'!he grassjforl:> fields had 33% of these orders in
the fescue-daninated fields
am
41% in the t.irtothy-daninated fields.
Haoopterans represented >30% of the insects captured in the fescue
mixed grasses habitat types.
am
Harqrt:erans in grassjfom fields comprised
only 10% of the total mnnber of insects captured.
All fields sarrpled
contained the sane relative mnnber (9-10) of insect orders captured.
cOOcentrations of insects were fOUl"Xi mainly aroun::i clllllJlS of forl:>s.
'"""'u
l11ble 1. J'rllf!Ortlon ClU of the '"~"P net
rep-es~ted by 10 lnuct orden and the percent••• of the fCMid
•
It~ brought to n~stllngs by eech bird !lpecles In 3 hebl et t~t (f•scue, MIRed erettet, and erase/forb) In northern llllnol1, July 1987.
ln~ect
Order
(172)
Homoptere
Olptere
Coleoptere
Hymenopt•r•
l•pldoptere
Arecnlde
Otthoptl'te
X Avell!tble
r~scue
H~lpt•n
II
Ocfonete
lleuropt•r•
Unidentified
HIRed gresses (207)
Momopt!!t8
Olptl'te
Coll'optere
Hymenoptl'ta
Lepidoptera
Arecnlde
Orthoptere
Hemlptere
Ocfoneta
II!!Utopl!!te
Unidentified
Gtesttforb (239)
Momoptere
Olptere
Coleoptl!tl
Hymenopt!!te
lrpldoptere
At11cnld11
Orthopter11
Hemlptl'rll
Odonlltll
lleuroptl!re
Unld!!ntlfed
3'-11
34.3
10.5
!1. 1
4.6
4.1
1.7
0.6
0.6
0.6
Hen!IIOV'I
Sperrov (IJ)b
.
10.1
31.2
2J.J
13.'
5.3
". 1
10.2
4.2
1.0
1.0
Gretshopper
Sperrov (21)
.
.
.
.
-
19. 1•
9.5
34.4•
3.4
42.8•
IJ.8•
-
C.7
3.C
..
.-
..
.
-.
.
.
.
2.3•
27.9
6.9
25.5•
13.9
16.2•
-
.
.
6.9
.
.
cr.8•
.
.
.
.
.
.
.
.
.
.
.
.
25. I
12.5
20.9•
4.2
n.3•
14.'
.
.
.
4.2
.
t~
Red· winged
lledblrd (24)
6.r
3.4•
34.4•
.
.
.
.
II
fotel number of Insects cRpturl!d In eech hebltet
fester•
"eedowlark (43)
ZJ.8•
14.4•
7.1•
Zt.3•
15.4•
7.7
311.5•
7.7
30.7•
SevltfYieh
Sperrov (Z9)
-
.
.
32.8
26.6
12.5
10.1
2.9
5.!1
6.7
1.9
0.0
0.5
tld:cls!lel (")
l1 •lven In perenthses.
b
Number of observetlons p!!t bird specll'!l Is tlven In perentheses.
• Slgrolflcent et .!'"0.05 (chl·tquare).
..
.
.
-
lobol lnt
22.2
u.4•
". 1
2z.z•
""'
-...J
48
DIS<lJSSION
--All~
the--sweep --salll>les were emers cutauon--to-
agricultural an:l oldfield habitats in Illinois (Wright 1955).
Birds were
not selecting insects in proportion to their availability.
'!he abundance of various prey types in a habitat influences prey
selection by foraging adults (Maher 1979).
through sweep sanples might
Insect availability detennined
not be a valuable irnex of the quanity of food
available to grasslan:l son;Jbirds.
Although nearly absent in sweep sanples,
lepidopteran larvae an:l orthcpterans made up IOOSt of the nestlings' diet.
Difficulty usually exists in matching field sanples with the diet no matter
how intensive an:l careful the field sanpling may be (Meunier an:l Bedard
1984).
Grasslan:l birds in OlPage Co. seem to select insects that are large
(>10nmt) an:l relatively easy to catch an:l CCil'lUOOn to oldfield habitats in
Illinois.
Henslow' s Sparrows fed Iepidcptera to nestlings 44% of the time
(Robins 1971b).
Grasshc:.pper Sparrows used Orthoptera 37% of the time
during May-August (Smith 1968).
the time (Judd 1901) •
Coleoptera (Bent 1958).
Dickcissels c::onsumeQ .Orthopterans 41% of
Eastern Meadowlarks consumed 26% orthoptera an:l 25%
Bol:x:>links fed nestlings 44% Iepidoptera an:l 14%
Orthoptera (Wittenberger 1980).
Red-winged Blackbirds fed nestlings
primarily Odonata an:l Iepidoptera (Robertson 1973) •
Similar nestling diets
for these species -were abser.ved in my study.
'!he stJWlY of food items present during the brood rearing period
seemed abunjant.
Evans (1964) concluded t.hat food
was superaburrlant in an
oldfield in Michigan in which Field Sparrows, Chiwin;J Sparrows (Spizella
passerina), an:l Vesper Sparrows (Pooecetes gramineus) nested.
49
More detailed evaluation of insect availability and nestling diets is
needed _at different stages -Of nes'tliD;}- developllet'lt d\lr.inEj-"theu-breeding
season.
Diet cx::aup::sition cllarges with the age of nestlings (Welsh 1975) ,
and insect availability fluctuates during
Sllil1ner.
50
~ONS
FOR GRASSlAND BIRD SPECIES AND GRASSlAND HABITAT MANAGEMENT
Habitat Management Options Available
'Ihe habitat management options available to the Forest Preserve
District of DJPa.ge County are IOCMing, prescribed fire, woody plant removal,
her:Dicides,
am
idling.
Mc:Ming can be an effective tool to create open
grasslarxi habitat at a low cost (Ryan 1986).
low labor intensity,
am
Advana.tges include low cost,
a large degree of control over the reduction of
the height of the vegetation
am
size of the area treate1.
Mc:Ming is
desirable, for it does not rem:we litter required for nesting for species
such as the Bdx>link
anj
Eastern Meadowlark, am those species requiring
short grasslarxi such as Uplarxi sampiper (Bartramia longicauda).
Mc:Ming should be tllred to reduce nest losses am the exposure of
imrrd::>ile Yot1Il3' to predation.
Mc:Ming should be co:rrlucted in late smmner or
early fall which will result in less destruction of g:rourxi nesting birds.
But IOCMing too late will reduce the aiOOUnt of winter am residual cover for
certain species of wildlife.
Mowirq sbculd first be COI'ducted on small
(5-10 ha) plots at varying heights to see which practice benefits which
grasslam bird species.
'!he major benefits of prescribed bunrlng will be control of invading
shrubs am trees, :rerocwa.l of litter,
(Wright am Bailey 1982) •
anj
increase of grasses
-anj
fo:rbs
'Ihe effects of fire on grasslarxi birds will vary
deperrling on intensity of bum, season, am habitat preferences of
irrlividual bird species (Ryan 1986).
Prescribed bums should be co:rrlucted
in early spring before nesting, when burning con:titions are best.
:nc>t
In areas
scheduled for woody plant :rerocwa.l, a 2-year rotation should be used for
6 years, with a 3-5-year rotation following, maximizing the .i.Irpact of the
51
fire on woody vegetation.
In areas where woody vegetation has been
remsved,----a- 3-5-year retation-sheuld--be used.- Fires- shO\:lld occur --before--15
April am should be scheduled to insure that no IIDre than half the site is
bun1ed in a year (Heidorn 1984) •
Altema.tive refuge habitats are important
for repopulaton on burned sites.
Fire will reduce litter depth.
Birds
needing a deep litter layer for nest placement, such as Henslow's Sparrow,
will be affected negatively by frequent fires; those preferrin;J open,
sparsely vegetated c.c>nlitions will benefit (Ryan 1986) .
Burned areas also
should be IIDnitored for vegetative an:i wildlife responses to the bum.
Woody
vegetation should be renDVed if it is exotic or if its renDVal
.
will maximize grasslan:i habitat but not reduce the natural quaility of the
biotic ccmnunity present.
Reiooval should be ac:::carplished by cuttin;J of
woody ste.ms >2.5 em with a chainsaw.
cut
ste.ms
should be treated with
hericides, such as Garlon, to prevent resp:routin;J.
should be cut with a brush hog or ha:rrl tools.
Woody
stems <2.5 em
'lhe sprouts from this
cuttin;J should be treated with a foliar spray of Rourrlu.p the followin;J
grow~
season.
All
~
should oc:cur in late f-all or wint:er ana should
stop before 15 March (Heidorn 1984) •
All woody material from these cuttings should be renDVed from the
management area, am chiiP=rl.
Manpower for both the cuttin;J am hauling of
woody material could be substantially reduced by usin;J Resource Management
voiunteers who are currently available to the Forest Preserve District.
Idle grasslan::ls are desirable for bird species selectin;J tall, dense
cover (Skinner et al. 1984).
free.
Idling areas is also cost efficient am labor
But woody vegetation invades am eventually daninates idle
grasslan::ls if no management is provided.
Idle grasslan::ls cannot remain
imefinately an:i still retain grasslam character (Skinner et al. 1984).
52
A canbination of management practices should be used.
Areas
should be
burned or IOCMed ani then_allowed to__Sfr for 2-3 y_ears for maxinnnn diversity
of bird species.
Bun1in;J or IIDWin;J should be
c:::on:lucte.d
on different
portions of fields in alternate years to allow llK)nitorin;J of population
levels of bird species.
Management for Grasslani Birds in D.IPage County
1) Preserve the largest existin;J grassy fields.
large fields
generally will hold llK)re grasslani bird species ani provide habitat for
area sensitive species ani ermngered or threatened species.
2) Create a llK)aSic of vegetation ani heights ani densities.
Irrlividual bird species JOOSt often selected areas on the basis of the
height ani density of the vegetation.
3) Reduce encroachi.rg woody vegetation.
Woody vegetation is
lll'Xiesirable to all grasslani bird species with the exception of the
Red-win;Jed Blackbird, ani should be kept to a minim.nn.
4) Corrluct various management practices on variOl.lS grasslan:ls.
Management practices that are available to the District ( idlin;J, burning,
woody vegetation rem::wal., herbicides, ani IIDWin;J) should be lll'Xiertaken in
sanple plots on grasslan:ls of various size ani vegetative c:x:.tnp:>Sition and
closely DDnitored for responses of irrlividual plant ani bird species.
5) Monitor grasslani study sites over len] periods of time.
'!his will
be the only way to evaluate habitat alterations ani establish long tenn
trerrls of abumance of many grasslani species.
6) FUrther evaluate habitat use by each grasslani bird species ani
DDnitor nestin;J success.
My study did
not evaluate nestin;J success of the
selected bird species, rut this is an i.n'p:>rtant aspect of bird biology that
53
Im.lSt be examined
to detennine the suitabilty of the various habitats
availabl~--
7) Use all the existin;J grasslani types available.
Different grass
species appeal to different grasslani birds for nestin;J ani foragin;J.
8) Protect areas where threatened or
observe:i in the past.
~ered
species have been
'Ihese areas contain the highest rnnnber of grassland
species ani their p:resavation is beneficial to all species of grasslani
birds ani other wildlife associate:i with grasslanis.
9) FUrther evaluate the inportance of residual vegetation for nestin;J.
I had a correlation between residual
CXNer
ani bl:"eE!dirg bird density, which
also has been established for nestin;J waterfowl.
10) F\lrther evaluate the :iJtp:>rtance of adequate sin;Jin;J ani lookout
perches as a limitin;J factor on grasslani bird aburrlance.
54
LITERA'IURE CITED
Habitat selection by breeding red-winged blackbirds.
Albeers, P.H. 1978.
Wilson Bull. 90:619-634.
Arrlerson, R.C. 1970.
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Polygyny in the dickcissel. Auk
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Appendix A. Field length, year~ of planting, and area of 21 transects within
3 habitat types in northern lll"nois, 1986 and 1987 •
..~
..
...
Field area (ha)
FiFld length (m)
Year planted
Transect area
Fesc~
8.9
18.2
20.6
35.2
40.5
52.6
64.7
87.1
411
594
502
548
937
1371
807
1828
1971/1972
1979/1983
1979!1983
1979
1978
1973
1979/1982
1976
5.1
7.3
6.2
6.7
11.4
16.7
9.8
22.3
Mixed grasses
8.9
13.6
18.2
28.3
40.5
0'1
0'1
396
457
411
1005
1096
1974
1974
1974
1974
1974
4.8
5.5
5.1
12.2
13.4
426
396
579
594
670
777
807
1035
1974
1973
1971
1983
1983
1971/1972
1978/1983
1978/1982
5.2
4.8
7.1
7.2
8.2
9.5
9.8
14.5
Grass/forbs
8.9
14.5
22.2
27.9
44.5
52.6
64.7
97.1
-~ndhll.
[email protected]
~r
•
It
of lndlvlclnll birch within @IICh tr-I!Ct In [email protected] llllnole, 1986 lind 1987.
Hebl tat type
Atl'll (he)
He~ I -
,.
GS
D
·(·)
·(·)
total
no. tpl'efl'l
I •
I"
Sll
6(3)
5(5)
3(5)
4(4)
5(110)
5(4)
6(6)
6(6)
3(3)
6(1)
5(2)
7(11)
10(110)
6(l)
9(5)
6(11)
·(2)
3(2)
5(3)
](1)
I(·)
5(9)
0(2)
~(liD)
11(7)
7(110)
4(5)
9(26)
19(JJ)
4(2)
4(4)
4(5)
5(5)
5(110)
4(])
,(2)
·(·)
·(·)
·(·)
·(·)
3(6)
4(1)
9(9)
9(110)
,(5)
1H
·(·)
·(I)
·(.,
·(·)
.(·,
11}(11)
5(110)
·(])
·(J)
·(7)
·(I)
·(·)
2(110)
·(110)
2(110)
·(·)
• (110)
2(1)
5(6)
11(11)
4(11)
4(4)
9(10)
19(9)
12(5)
2.2,
3(4)
3(4)
1(-)
1(3)
6{3)
4(1)
1(1)
-(-)
·(·)
·(·)
·(·)
·(·)
·(·)
-(-)
·(·)
·(·)
3(J)
I( I)
1(-)
1(l)
3(2)
·H
·(I)
·H
·(·)
·(·)
·(·)
·(·)
·(·)
100
"
60
10
35
""
IS
liS
~r
OftlSity
(birch/he)
1(1)
ZCZ)
7(5)
1(·)
·(·)
·(·)
·(1)
·(-)
·(·)
·(·)
·(110)
·(110)
11(6)
17(15)
17(13)
16(111)
29(HD)
211(24)
30(411)
40(60)
0.26(0. 19)
0.311(0.34)
0.45(0.34)
0.39(0.44)
0.42(110)
0.211(0.23)
0.50(0.110)
0.30(0.44)
10(5)
17( 14)
15(15)
36(40)
26(110)
0.34(0. 17)
0.50(0.41)
0."(0.49)
0.411(0.53)
0.32(110)
17(16)
14(15)
22(14)
36(33)
32(33)
30(29)
60(311)
62(611)
0.54(0.51)
0.411(0.51)
0.51(0.32)
0.111(0.74)
0.64(0.66)
0.52(0.50)
1.00(0.63)
0.70(0.77)
fUCUI'
11.9
111.2
20.6
35.2
40.5
52.6
64.7
117.1
Hhted gr •~ses
11.9
13.6
111.2
211.3
40.5
Grllsstforbs
11.9
14.4
22.2
27.9
44.5
52.6
64.7
97.1
3(4)
4(5)
4(3)
7(6)
7(6)
5(7)
5(5)
4(4)
Frl'quency of Occurr!'ncl' (%)
-II
10( 10)
3(5)
~(6)
4(7)
·(I)
·(·)
5(9)
3(l)
·(I)
1(-)
-(-)
·(·)
·(1)
·(·)
·(·)
·(·)
-(-)
·(-)
·(·)
zen
• (110)
7(110)
6(8)
4(6)
ZC2J
-(-)
-(-)
2( 1)
1(1)
·(·)
·(·)
1(·)
4(3)
3(])
15(10)
8(110)
Z(·)
3(-)
2(1)
2(3)
• (110)
·(·)
·(·)
I
2(1)
J
5(2)
·(·)
·(·)
3(1)
3(1)
5(10)
0(2)
-(-)
IJ( IZJ
4())
5(2)
17(11)
17(19)
11( 10)
34(26)
44(52)
10
98
70
2.5
·(liD)
·(-)
·(·)
.()
1(110)
1(·)
3(5)
4(9)
-(-)
·(-)
·(-)
-(-)
·(·)
·(·)
·(·)
1(-,
J(J)
-(-)
·(·)
·(NO)
·(·)
·(·)
.(-,
·(·)
·(·)
EH • £nstern Headowl11rlt, SH" Sev1tnn11h SJ>'rtow, FS • rl!'ld Sparrow, D • DlcltciUI'1, ltU • lted·wlnged lhckblrd, SS" Song Spsrrow,
HS • H!'nslow's Sp3rrow. MD (no date) lndlcet!'s fll'ld .,., not surv!'Yf'd In 19117.
I • Bobolln~,
b
Data from 19117 In parentheses.
0'1
.....,J
a
Appendix C. Non-grassland birds seen or heard during bird surveys in
3 habitat types in northern Illiinois, 1986 and 1987.b
Bird species
Fescue
Eastern Kingbird
Barn Swallow
Tree swallow
Red-tailed Hawk
Northern Harrier
Common Crow
Common Grackle
Yellow Warbler
Mourning Dove
American Kestrel
American Robin
Brown-headed Cowbird
American Goldfinch
Common Yellowthroat
European Starling
American Killdeer
Northern Flicker
Brown Thrasher
Sedge l.lren
Chinnney Swift
Gray Catbird
Ring-necked Pheasant
+(+)
+(+)
+(+)
+(+)
-(+)
+(+)
+(+)
-a
+
= presence,
-
= absence.
b
Data from 1987 in parentheses.
Mixed
grasses Grass/forb
+(+)
+(+)
+(+)
+(+)
-(-)
-(-)
+(+)
+(+)
+(+)
-(+)
-(+)
-(+)
-(+)
+(+)
-(+)
-(+)
+(+)
+(+)
-(-)
-(-)
+(+)
+(+)
+(+)
+(-)
+(+)
-(+)
-(+)
-(+)
+(+)
+(-)
+(+)
-(-)
-(+)
-{+)
-(+)
-(+)
+(+)
+(+)
+(+)
+(+)
-(+)
-(-)
+(+)
-(+)
+(+)
+(+)
+(+)
-(-)
-(-)
+(+)
+(+)
+(+)
-(+)
-(-)
-(-)
-(-)
-(-)
+(+)
+(+)
0"1
(X)
p
E
R
C
78
GO
E
"
T C 58
() 0
lll!B f)J.L
G
E t1 40
t1
0 u
GR()SS/FORD
FIELDS
•
F H 38
I
T IMOTIIV
Jill FESCUE
T T
II V 28
E
B
18
I
n
))
~
w
()
5
G
7
9
9
BIRD SPECIES
Appendix D. Percentage of the total bird community represented by 9 bird species
in all grass/forb fields a~d those dominated by timothy and fescue in northern
Illinois, 1986-1987.
l~Bobolink, 2~Eastern Meadowlark, J~savannah Sparrow,
4~Grasshopper Sparrow, s~otckcissel, 6~Red-winged Blackbird, 7~Song Sparrow,
8~Henslow's Sparrow, and 9~Field Sparrow.
70
FESCUE
18
I
i
11IXED GMSS
'
iI
'
I i
'
I
18
'
!
~
, I
I
I : :I
:i
I I i
I ! II
I II
II
f-n1
I Ill I II
I
I
I
II
I
I
_l)
I
IJ
I II
...i
I
I
GRASS.tFORB
I
18
I
I
l I
I
I
l
i
'
i
IJ
' I
I
;
II
I
I
I
!I
I
I I
!
II
'
I
!
I
)1
11
II
I
I
II
I
II
1
II
I
I
' ll
I II
I I Ill
I
~
0
~
aJ
..0
E
z:::3
1
1
18
188
1
1
18
188
1
1
18
Area (ha)
1\j?pendH -£.
Relationship between habitat area and the
number of bird species in 3 grassland habitat types in
northern Illinois, 1986-1987.
188
71
FESCUE
GRASS/FORB
"IXED GRASS
188
188
188
18
18
rn
.-j
ClS
:::3
'0
·o-1
>
·o-1
'0
c
H
18
.
1.1-1
0
.
;..
v
l-1
• I
IV
Q)
..Q
e:::3
z
~
1
18
1
188
1
18
1
188
1
.
.
..
1
I
18
.
.
188
Area (ha)
Appendix F.
Relationship between habitat area and the
number of Bobolinks in 3 grassland habitat types in
~---T,Inorthern
I llineis,
1~86-19-87.
72
GRASS/FORB
"IXED GRASS
FESCUE
188
188
m
rn
rm
Cll
r-l
co
::s
'0
·r-i
:>
·r-i
'tl
18
.
~
.
18
·r-i
7~
4-l
1-1
G)
..0
---~-~~
s::s
z
v
.~./
0
l
t
1
Appendix G.
18
.
188
~
l
1
18
188
~.Li±tlwt:...;..t..•_.
1
18
. '
180
Relationship between habitat area and the
number of Eastern Meadowlarks in 3 grassland habitat
types in northern Illinois, 1986-1987.
73
FESCUE
GRASS/FORB
rtJXED GRASS
188
188
188
.
en
.......
co
:s
I
~
·.-t
>
18
18
18
·.-t
'0
s::
H
1+-1
0
,..
.
I
~
.V
1
.
v
v
L
1
1
Q)
.a
8
:s
z
v
1!.1
1
18
188
8.1
1
18
188
8.1
1
18
188
Area (ha)
Appendix H.
Relationship between habitat area and the
number of Savannah Sparrows in 3 grassland habitat types
---in northern Illinois, 1986-1987.
74
FESCUE
It IXED
18
.
en
,-j
I
cU
I I
:::l
'tl
·.-I
>
·.-I
c:
I
H
I
4-j
'-~
I
l1.
1
8.1
ILl ~
~
Q)
18'ml§ll
1-·
. I
1
'tl
0
,....
GRASS/FORB
GRASS
18
8.1• •
..0
E
7
:::l
7
:z
lUll
1
18
188
8 . 81 J..-...L....J...U..U..W.--l--'-.L..I..I.IWJ 8 . 81
1
18
188
1
18
188
Area (ha)
Appendix I.
Relationship ce:tween habitat area and the
number of Grasshopper Sparrows in 3 grassland habitat
types in northern Illinois, 1986-1987.
75
,IXED GRASS
FESCUE
188
GRASS/FORB
188'~-
188
I
I
II
18
'+
44
0
I
j
).j
-
1-- 1-
<V
..a
e
::s
.
:z
1
.
1
18
188
1
!LV
1
18
188
1 ~.J..J...L.L.I.wL.--l...J...I...I..I.Wl
1
18
180
Area (hal
Appendix J.
Relationship between habitat area and the
number of Red-winged Blackbirds in 3 grassl~nd ha~itat
- - -
types in northern Illinois, 1986-1987.
AflP81dlx IC.
Plent speelet eeeurrlng vlthln fti~UII CtJ, 11llltd ' ' " ' " C!,, end trMt/forb CJ, hlbltet trpH In northern llllnolt, 1986·87.
CommrtNIIIII!
Scientific , _
llebltat type
c--
telentlfle , _
Meadou fescue
Orch~d gran
s-th b r rentucky bluegrass
llel!d cenery grass
llt'dtop
Clullckgreu
.. ..,thy
foxtails
resetuea elatlor
Dactyl It gl-rata.
lrGIIQS lner11l1
Poe prati!Mit
Phal ar II arundlnac+a
Agrostlt alba
Agropyron repent
Phll!llll preti!Me
Setaria
I,!,J
I,Z,J
I,Z,J
I,Z,J
1,2,3
Z,J
I,Z,J
1,2,3
I, J
Cattell
Oul!en·anne't·lace
Daley flellblnt
Vlld bere-t
Cray-headtd coneflower
Yellow sueet clover
Uhfte !IWI!et ciGver
llt'«f CIGver
Uhlte ciGv~r
Alsfke ciGver
Yl!lfON hop ciGver.
Cllhlldfl thistle
lui I thistle
lloddlng thistle
Comnon r egwetd
Clent reglll!l!d
Field blndlll!l!d
lll!dge blndlll!l!d
c--. sow thistle
Splny-leiiYI!d sov thistle
IIGrse nettle
llttersveet nlghtKhede
Vlld pennlp
Melli otus of fie Ina lit
M. elba
lrlf«tlluw preti!Me
t. repens
I. h.,.,.ldluw
I. egrar 11111
Clrsluw ervense
c. vulgare
CGrruus nutAllfJrGsla artl!lllsl ffol Ia
11. trifid•
CGnYGiwlus arvenslt
c. seplllll
Sonchus olereeeus
s. esper
SGienum carGIInenst
S. clllc-ra
Pastfneca sativa
Apeeyruw llll!df1111
lluwex crfspus
Arctl1111 11fnut
liiCtuca [email protected]
OenGthera blernlt
PlentegG mejGr
SGI ldagG spp.
Freger I • vi rglnfantl
I,Z,J
I,Z,J
1,2,3
t,Z,J
t,Z,J
1,2,3
t,Z,J
J
J
I,Z,J
J
I,Z,J
t,!,J
1,2,3
1,2
l'n!h• latlfolla
Oaueus earota
1,2,3
Er leer on lni1UUI
1,2,3
Monardl flttulosa
1,2
llatlblde pinnate
I
Mentha plperate
I, J
I
Abut lion thellflhralt I
Achlll Ia •lllefollllll
I, J
1,2,3
Potent Ill •
Prunella wlger It
I
Verbesc1111 thespus
I, J
v. blatterl
J
laraucuw offlclnale
t,Z,J
1,2,3
Pol n - •rP·
o.. llt europe•
1,2
llem.reeellls fulve
2
Pertheneellsus qulnquefolle 2
A1elepla eyrfca
I,Z,J
A. vertlelllet•
J
lrttopGgen pratensl•
Z,J
Clrhorl1111 lntybus
2,J
Chrysenth-.w leueanth4!11U11 1,2
Chl!nopGdltJII elba
1,2,3
Verbena urtlclfolla
Z,J
v. hastata
2
letpedera lflP.
J
D~t~bllne
Cur led dGclr
lurdGch
Vfld lettuce
Evening prlmrGse
CGIIIIIOI'I plenteln
GGidenrGdK
Vlld str11wberry
'A'·
'·
'·'
'·
J
I,Z,J
I
J
I,Z,J
I, J
I,Z,J
I,Z,J
l
I,Z,J
2
P~flllnt
Ve.lvetleaf
Yarrow
Cinquefoil
lleel·•ll
ComnoniiQIIeln
MGth IIQIIeln
Dendl!l l«tn
s...rtlll!td
YeiiGV VGOd torrel
Dey lily
Vfrtlnla crnper
Clllflllanllllhl!td
Uh~trltd •lllrlll!td
Yellow to•t• bl!trd
Chld:ory
011·eye daley
quartert
Uhf tl! vervain
tlue vervain
lush e I over
t•••
llasJ!bl!rry
tladbl!rry
Mult If I ora rose
Pasture rose
Vlld grape
IGxelder
Sliver ~~~~pit
Vlflov
Eastern cottonVGOd
Nebltat type
'f'P·
"""" lflP.
...... lflP.
llosa ..,ltlffGra
1. carolina
VI tus !lflP.
Aeer negundG
A. 11ceerfl'tllll
Sal hi lflP.
Populus deftGides
t,Z,J
2
1,2,3
I
1,2,3
t,Z,J
J
I, J
2,3
-...J
0'1
--!
SU""ER "EASURut(ftiS
SFIUIG "[ftSURutUtiS
Grass height (em)
Ul
1'1·
1'1
141
141l
141
lZI
121
121
UKf
UN
Ill.~.
18
18
18lf
'8
"
4U
A
,,_,_______.._____. __ ,_...:_.
1
z
J 4
·flftRilftT TYPf.
,.
41
41
21
21
-..J
-..J
f
21
Appendix L.
BIRD SELECTIOH
5
I
I
_,
·2 ] •
HARITAt-TYrr.
-f
5
11---• '
'
- - - - - '
RIRD
-l~
7'
~P[CI[~
Means, standard deviations, and ranges of grass heights for 5 grassland
habitat types during spring (March) and summer (June-July) and around songposts of 7
species of grassland birds in northern Illinois, 1986-1987.
Habitat types: !=fescue,
2=mixed grasses, 3=grass/forb, 4=fescue-dominated grass/forb, and S=timothy-dqminated
grass/forb.
Bird species: l=Henslow's
Sparrow, 2=Dickcissel, )=Savannah Sparrow,
I
4=Grasshopper Sparrow, S=Eastern Meadowlark, 6=Red-winged Blackbird, and ?=Bobolink.
zoo,
Forb height (em)
srRUIG ftEftSDRlftotiS
zn
SUnftll ftUSUilftDOS
IIKD ULECTIOH
~
ZUI
151
n•
n•
u•
Ill
Ill
51
5I
11---•-•-•-•--' I •~-------_.,.-4
I Z J 4 S
I Z 3 4 5
Rftlllfti-IYFE
RAIIIII-IIPl
Appendix M.
habita~
Means, standard deviations, and ranges of forb heights for 5 grassland
types during spring (March) and summer (June-July) and around songposts of 7
species of grassland birds in northern Illinois, 1986-19S7.
Habitat types: l=fescue,
2=mixed grasses, 3=grass/forb, 4=fescue-dominated grass/forb, and S=timothy-dominated
grass/florb.
Bird species: l=Henslow's Sparrow, 2=Dickcilsel, 3=Savannah Sparrow,
4=Gras~hopper Sparrow, S=Eastern Meadowlark, 6=Red-wingect Blackbird, and 7=Bobolink.
Height Density (dm)
.
1111 ULlCIIOH
Slftftll MIASIIlftlHIS
•riiHG ftlASIIlnlHIS
II
II
II
'I
'I
'I
1
1
1
'
5
'
5
'5
4
4
41
3
2
31lf
z
I
1
::tt tt
dL
-..I
1.0
··-·---1-t-11 I I I I I I- 1 - z 3
I 2 3 4 5
I Z 3 4 5
1111111 ltrr.
Appendix N.
Hllllll-ltPi
~ 5 ' 1
1111 SPfCIU
Means, standard deviations, and ranges of height-density for 5 g~assland
habitat types during spring (March) and summer (June-July) and around songpostis of 7
species of grassland birds in northern Illinois, 1986-1987.
Habitat types: !~fescue,
2=mixed grasses, 3=grass/fo~b, 4=fescue-dominated grass/forb, and 5=timothy-d~minated
grass/forb.
Bird species: l=Henslow 1 s Sparrow, 2=Dickcissel, 3=Savannah Spar~ow,
4=Grasshopper Sparrow, 5=Eastern Meadowlark, 6=Red-winged Blackbird, and 7=BoQolink.
srRIIIC ft[ftSIRJJDIIS
u
u
SUftftlR RtASIRlRIHIS
u
14
14
14
lZ
1Z
1Z
11
11
11
I
I
I
'
'
4
4
'
z
z
z
II RJ SlLlCII9H
Utter depth (em)
,, __ ,__ ,_,_ __.___. II
I
Appendix
o.
Z J
4
nnnnnt nrf.
S
00
0
4
'
'
'
1 z 3 4
'
5
• It
-l
- 2 l 4 5 ' 1
BIRD
Rllllll-ltrf.
'
sncns
Means, standard deviations, and ranges of litter depths for 5 grassland
habitat types during spring (March) and summer (June-July) and around songposts of 7
species of grassland birds in northern Illinois, 1986-1987.
2=mixed grasses,
grass/forb.
3=grass/fo~b,
Habitat types: l9fescue,
4=fescue-dominated grass/forb, and 5=timothy-dominated
Bird species: l=Henslow's Sparrow, 2=Dickcissel, 3=Savannah SparDow,
4=Grasshopper Sparrow, 5=Eastern Meadowlark,
G=Re~-winged
Blackbird, and ?=Bobolink.
I
'~l-111-411-
IUU '~
1
m
"
11
II
11
Grass coverage
cover class
.
IIRD ULlCIIOII ...
SUIVI[I nEASUIUIUIIS
srRIIIC "f.ASURUit.HIS
J
I.
•
2 l
4 5
UARilftT TYrf.
Appendix P.
f
H~l
:
I I I I Ill I Ill I 11B
11
"51 l
"51
41
41
41
ll
ll
]I
2
Zl
21
II
II
~~-•---•-·-~~1 ~I_,__.__,_-,_-II
l
~
"
51 l
.I
2
'I llllTr 111 JJLJ. I::
IOU
1
z l 4 5
z
% coverage
21
II
I11__-_____..___. __._, ___,_,,
1 z l 4 5 ' 1
IIID UJfiU
liAR II AI -fYPf.
Means, standard deviations, and ranges of grass cover (%) for 5
grassland habitat types during spring (March) and summer (June-July) and around
songposts of 7 species of g~assland birds in northern Illinois, 1986-1987.
Habitat types: 1=fescue, 2=mixed grasses, 3=grass/forb, 4=fescue-dominated
grass/forb, and 5=timothy-dominated grass/forb.
Bird species: 1=Hens1ow's
Sparrow, 2=Dickcissel, 3=Savannah Sparrow, 4=Grasshopper Sparrow, 5=Eastern
Meadowlark, 6=Red-winged Blackbird, and 7=Bobolin~.
2=5-25, 3=25-50, 4=50-75, 5=?5-95, and 6=95-100.
Cover classes (%): 1=0-5,
00
I-'
SU""ll RIASURlftfnl1
URIIIC ftf.ftSDRDifHIS
Ufl'
5
'
5
II
II 4
71
Forb coverage
J
51 J
"
.IUU
41
41
]I
]I
I"
II
4
I JJL
$1 J
111
rh
l
I
61 %
~
41
]I
21
z
Ull I Ill Ill I LJ1 11f1 zu
II
II
II
I
uL-.
-- ·--~-·--~·-~-''
I Z
l 4 5
i
IIARIIAf lYI'F.
I
lll+'_,_l!!_,~_,__!.-!1_,_._,,
I
Z l
4 5
IARIIAJ-1Yrr.
I
IL'-•-•-~•--'-·-Y!·-'-·~-'
I Zl 4 5 ' 7
IIRD
co~erage
51
21
2
2
r·
5
11
"
cover class
'I
"Im
"
4
Appendix Q.
lUI
IIRt ULfCliOH
U
~r£(1[~
Means, standard deviations, and ranges of forb cover (%) for 5
grassland habitat types in spring (March) and summer (June-July) and qround
songposts of 7 species of grassland birds in northern Illinois, 1986-1987.
Habitat types: l=fescue, 2=mixed grasses, 3=grass/forb, 4=fescue-dominated
grass/forb, and
5=timothy-do~inated
I
grass/forb.
Bird species: l=Henslow's
Sparrow, 2=Dickcissel, 3=Savannah Sparrow, 4=Grasshopper Sparrow, 5=Eastern
Meadowlark, 6=Red-winged Blackbird, and 7=Bobolink,
2=5-25, 3=25-50, 4=50-75, 5=~5-95, and 6=95-100.
Cover classes (%): 1=0-5,
CXl
N
srnmc nF.RSIIRt.nF.tns
'
HJV.
IUU'
"
"
II
4
Bore ground
cove•· class
l
Appendix R.
4
"
II
4
71
71
"51 ]
"51 3
"51
41
41
48
31
]I
JB
~lt.•t ~fl;::
2" '-]"··--.-·-',-11
IIRHilftf
II
IUU
71
2
I
,..
5
5
5
IIRD ULECIIOII
SltMF.R ftUSIRlftUIIS
I
z
Zl
II
I
8L!_,_'f_,_,__ ,_L_,_.__,,
I
nrr.
Z J 4 5
OllilA I-Uff.
z
•
'Jr, coverage
28
11
,,._, __ ,_L,J '• ,_ -• • I U
I ZJ 4 5 ' 1
1111 Uf.Cif.S
Means, standrad deviations, and ranges of bare ground cover (%) for
5 grassland habitat types during spring (March) and summer (June-July) and around
songposts of 7 species of
gr~ssland
birds in northern Illinois, 1986-1987.
Habitat types: l=fescue, 2=mixed grasses, 3=grass/forb, 4=fescue-dominated
grass/forb, 5=timothy-dominated grass/forb.
Bird species: l=Henslow's
Sparrow, 2=dickcissel, )=Savannah Sparrow, 4=Grasshopper Sparrow, 5=Eastern
Meadowalrk, 6=Red-winged Blackbird, and
7=Bobolink~
2=5-25, 3=25-50, 4=50-75, 5=75-95, and 6=95-100.
Cover classes (%): 1=0-5,
co
w
-~h!l. Ft~ney of me of pl11nt tpeelet or tltet
, In northern Illinois, "ey·June 19!17.a
lobol lnlt
r .. rch 8peell!s
or !lite
Grotnf
Shrtk!l
Sow thlstll!
Thistle
Oogbene
Feseue
Y. SVI!I!t elovl!r
II. eenery gress
C. MJiteln
Vlld lettuee
htett
OUPI!n·llnnl!!!·leee
"flkWI!I!d
Unknown forbs
fl!neel lne
FencepoUs
Sunflovert
Evening Primrose
It Mil!
Orcherd gren
Trees
Signs
llndweed
curled Dock
C11tt11ll
Rllgwetd
Ttell ~n~~rlters
Power I In!! tower
Goldenrod
Cement posU
Vood!!n Slllki!S
Thnothy
TeiO'phone wires
F
(70)
l5.7
ll.8
10.0
4.3
8.5
8.5
7.1
5.7
4.3
2.8
2.8
2.8
2.8
1.4
:by
treulllnd birth In fHeut ,,, •hied trHtH
fll!ltern "•edowlerk
Me
(ll)
3.1
31.2
CF
(1l9)
F
<8U
7.7
23.2
0.8
6.9
5.4
39.5
20.9
.
.
3.1
0.8
2.5
6.9
6.2
3.1
0.8
3.1
Z.5
3.7
2.5
1.6
3.3
7.8
.
3.t
.
Z.5
.
15.6
6.2
12.5
15.6
.
9.J
.
11.6
13.1
1.5
2.J
.
.
.
.
.
.
1.5
0.8
0.8
.
.
.
.
"G
(60)
JJ.3
30.0
1.6
.
.
.
.
.
.
.
.
GF
(39)
U.5
20.5
.
.
5.1
.
.
.
5.1,
5.1
.
.
.
.
.
1.6
.
.
.
Z.5
.
.
.
24.1
11.6
7.8
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
8.]
6.7
1.6
.
.
.
.
.
.
.
.
.
.
.
.
.
.
,
!levltnnllh !lperrov
Crltlhcpper !lperrov
Me
OF
,
(l08)
(29)
(27)
(9)
9.6
18.7
1J.9
9.1
3.8
5.3
6.7
3.4
51.7
7.4
18.5
.
1.0
.
4.3
6.7
5.3
3.3
.
1.4
3.J
1.9
1.4
1.0
1.0
1.0
1.0
.
.
.
.
.
.
.
.
.
-II
lot11l number of birds observed In l!llch h11bltet type by species Is given In perenthetl!!l.
.
.
.
.
.
.
.
.
10.3
3.4
lind trHt/forb (OF) cb'lng tr-ec:t eomt1
(M),
.
.
3.7
.
.
.
.
14.8
7.4
.
.
.
.
.
55.5
.
.
IZ.Z
.
.
.
.
.
.
.
3.7
.
.
.
44.4
.
J.4
.
.
.
.
.
11.'.
.
10.3
.
.
.
.
.
.
.
6.9
.
6.9
3.4
.
.
.
11.1
.
.
.
.
.
.
.
.
.
.
.
.
.
lttd·vlngtd llaekblr~
GF
,
"G
(9)
(52)
(38)
OF
(357)
15.4
30.7
5.8
1.9
3.8
18.4
31.5
3.3
18.5
2.6
20.4
11.7
.
.
.
.
.
.
.
.
.
.
22.2
.
.
.
1.9
.
.
2.6
.
.
.
1.9
1.9
.
1.9
2.6
.
0.3
0.3
1.4
0.3
3.3
3.1
8.1
0.3
0.8
1.9
.
.
.
J.8
2.6
5.2
.
8.4
Z.2
23.1
23.6
13.4
.
2.6
1.1
.
.
.
2.6
5.Z
0.8
.
.
.
.
.
0.3
0.5
JJ.3
.
.
.
44.4
.
.
.
.
.
.
1.9
.
.
.
.
J.8
co
~
Appendix T.
Song perch use (percentage), mean perching and\ singing heighta for 7 grassland bird species in northern Illinois, June-July 1987.1
Dickcissel (N=11)
Henslow•s Sparrow (N=9>
Queen-Anne•s-lace
~- Sweet clover
Y. sweet clover
Dogbane
Multifora rose
Orchard grass
Perch height
Singing height
33.3
22.2
11.1
11.1
11.1
11.1
132.6 (24.3)
89.6 (12.5)
Shrubs
Evening primrose
~i ld lettuces
Asters
Queen-Anne•s-Lace
Bull thistle
Goldenrods
Sow thistle
Unknown forbs
Perch height
Singing height
Bobolink (N=14)
18.2
18.2
9.1
9.1
9.1
9.1
9.1
9.1
9.1
Goldenrods
Multiflora rose
Coomon mi l kweed
Shrubs
~ild lettuces
~ooden stake
42.8
21.4
14.3
7.1
7.1
7.1
Perch height
Singing height
126.7 (43.8)
115.3 (31.1)
15~.9 (29.1)
145.4 (34.1)
Eastern meadowlark (N=28)
savannah Sparrow (N=24)
Grasshopper Sparrow (N=16)
Bull thistle
Evening primrose
Sow thistle
Shrubs
Coomon mi l kweed
Fallen tree top
Goldenrods
~i ld lettuces
Fescue
Perch height
Singing height
Red-winged Blackbird (N=34)
18.8
12.5
12.5
12.5
12.5
6.2
6.2
6.2
6.2
108.4 (23.4)
97.3 (21.1);
(X)
U1
Multifora rose
Canada thistle
Shrubs
Goldenrods
Trees
Evening primrose
Conmon mullein
Posts
~i ld .lettuces
Sow thistle
Unkown forbs
Perch height
Singing height
20.8
16.7
12.5
12.5
8.3
8.3
4.2
4.2
4.2
4.2
4.2
Shrubs
Multiflora rose
Trees
Coomon mi l kweed
Trail markers
Dogbane
Canada thistle
Bull thistle
Telephone wire
Unknown forbs
141.9 (86.4)
116.9 (41.3)
Perch height
Singing height
a
Mean (SO) for perch height and singing height (em).
32.1
14.3
14.3
14.3
7.1
3.6
3.6
3.6
3.6
3.6
219.1 (204.8)
20<1.5 (198.2)
Shrubs
Dogbane
Trees
Burdoch
Goldenrods
Multiflora rose
Sunflowers
Evening primrose
Asters
Coomon milkweed
Giant ragweed
Bull thistle
Unknown forbs
Perch height
Singing height
17.6
11.8
11.8
11.8
8.8
5.9
5.9
5.9
5.9
5.9
2.9
2.9
2.9
191.1 (96. 1)
176.5 (37.2)
86
.Appeirli.x U.
Perch Use by Grassland Birds in Northern Illinois
MEIHOI:S
Fields were sm.veyed for birds by wal.kirg straight-line transects at
about 20
nVmin.
Bird species, sex (when distin;Juj.shable), and the plant
species or object used as perches by in::lividual birds within 60 m on each
side of the transect were recorded 21 Ma.y-10 June 1987 (Emlen 1971, 1977,
Mikol 1980).
Bird centered vegetation scmplin;J was corrlucted 15 June-10
July 1987, between 0530-1200 hours.
I recorded the plant species or object
used as a perch, height of the~' and the height of the sin;Jin;J bird
.
above the gra.m:i.
Songposts of in::lividual birds were located by
systematically traversin;J entire fields 15-19 June 1987.
:u:x::ations of
in:lividual songposts were marked with flaggin;J tape (Iarson and Bock 1986).
No statistical tests were done.
RESULTS
Farly in the breed.in] season (May) <kim fom stalks
used as perches by IOOSt bird species.
-am shz'Ubs
were
Birds used new foro growth as it
became available later in the breeclin;J season (June-July).
Seven bird
species in 3 habitat types used 24 plant species, 6 man-made objects, and
the gra.mi (.Apperrli.x s) •
Shrubs were used 21% of the time, and the grourrl 13% of the time by
the 7 bird species in the 3 habitat types.
With the exception of the
Grassl1q:per Sparrow', I observed all bird species on the grourrl.
'lhe
Eastern MeadCMlark used gra.m:i perches (39%) 100re than any other bird
species (,E<0.05) (.Apperrli.x S).
87
Alt:hol.¥jl no statistical tests were done, d::>sel:vations in:licated trends.
Shrubs
-were used b¥ the
RsdwiD:Jed
an:i Dickcissel nost often.
mackbim, Bel3oliHk, Savannah Sparrow,
Fo:r:bs were used exclusively by the Grasshopper
Sparrow an:i Henslow' s Sparrow.
Perch species an:i height
were recorded in the bird centered vegetation
survey, which was corx:lucted 2-4 "Weeks later in the
b~
season than the
censusues.
'!he Bobolink used
available.
Eastern Meadowlarks used the groun:i less often than they had
earlier.
IleW'
growth of goldenrod cl1.lllpS as they became
Sixty percent of the birds observed on the groun:i earlier in the
year were females.
process began.
Females became 100re secretive as the brood rearing
Males singing fran elevated perches were the only
in:lividuals sanpled.
'!he Eastern Meadowlark selected the highest perch and
singing height of the 7 bird species, an:i the Grasshopper chose the lowest
perches.
species
'!he Henslow's Sparrow had the lowest singing height of tlte 7 bird
(~
T).
I abserved 4 singing height groups: <1 m contained Grasshopper Sparrow
CiOO Henslow' s Sparrow; 1-1.5 m contained
Bcbol~ SavaJmah ~, ani
Dickcissel: 1. 5-2 m contained Red-winged Blackbird; >2 m containted Eastern
Meadowlark
(~
T) •
Alt:hol.¥jl all bird species differed to sane extent on the frequency of
use of certain substrate types for singing, overlap occurred in the use of
substrate type an:i at times of specific perches.
In sane cases irrlividual
perches were used by several species, an:i the 100re aggressive encot.U'lters
between species were noted at~.
Eastern Meadowlarks an:i
Red-winged Blackbirds exhibitied specific t.errlencies, preferring the
highest avaiable perch, an:i the other species preferred perches of a
certain height rarge above the vegetation.
,
88
DisaJSSION
Basea-<>n
the-data-available, grasslan:l-son:Jbirds seemto choose
perches mainly on their height above the vegetation, rather than a specific
plant species or object.
Arr:f natural or man-made object that projected
above the vegetation was suitable.
Harrison (1977) concluded that
grasslan::i associated birds use any elevated perch structure < 2 m tall.
Although 2 species frequented the grourrl (Eastern Meadowlark an::i
savannah Sparrow), an::i 1 delivered its so:rg often in flight (Bobolink), the
presence of perches is essential to grasslan::i birds for si:rgi:rg an::i
absel:vation posts.
Perch sites might be ilrp::>rtant as si:rgi:rg posts for
open country passerines without aerial flight so:rgs (Cody 1985). Robins
(1971a) noted the presence of perches affected habitat quality for
Henslow's Sparrow, Schroeder an::i Salsa (1982) stated that ideal habitat for
Eastern Meadowlarks contains 4 perches/!. 2 ha.
Harrison (1977) fourrl Eastern Meadowlarks exemplified the
generalization that higher perches will be used instead of smaller ones.
'!he-~ Sparrow,
will l'lOnllally select the hi(jhes't pere.h available
(Smith 1963, 1968; Weins 1973).
perches 88% of the time.
Harrsion (1977) fourrl they used lower
Of the 7 bird species in my study, Grasshopper
Sparrc7NS selected the lowest perches.
Henslow's Sparrc7NS usually si:rg
just belc::M the general vegetative cover (Robins 1971a).
I fourrl Bobolinks
preferred stalks of goldenrod as perches, as did Joyner (1978).
Weins
(1969) in Wisconsin noted the use of .irrlividual perches by several species,
am aggressive
encounters aroun:i ~·
89
My study suggests that
grasslam
they use as a ~ substrate-.
am
birds are not selective about what
:BI.lt the presence -ef ava-ilable perches
their height above the vegetation appears essential for singing
observation posts
am
am
should be considered in management of grasslams.
90
Appentix V. Mana.genent Rec::onuneOOations for Irxlividual Bird Species
Henslow'' s Sparrow
Managenent of Henslow's Sparrow is scmewhat canplex.
'!hey tend to
breed in loose colonies of .::::;12 pairs, arrl. they can be present in a certain
locality arrl. absent fran a similar habitat nearby (Hyde 1939).
Robins
(1971a) fOUl'rl 58% of suitable breeding habitat in Michigan uncx::cupied
during the breeding season.
Also, the type of habitat required by
Henslow's Sparrows is seldan available, because few fields are idled long
enough to produce favorable corrlitions (Robbins et al. 1986).
1) Protect identified sites where this species has bred in the past.
'Ihe protection of grasslarrl. nest sites in association with grasslarrl.
management programs are major requirements for protection of Henslow' s
Sparrows (Bowles arrl. '!han 1981).
2) Maintain large fields.
Samson (1980) lists Henslow's Sparrow as an
area sensitive species requiring large grasslarrl. tracts for ensured
sm:vival, usually >10 ha in size.
studies in Chio suggest a positive
correlation :between distance to field edges ani the rnnnber
of_
Henslow's Sparrows present (Nolin arrl. Ritzenthaler 1987).
I fOUl'rl
pairs of
Henslow's Sparrows exclusively in large (>50 ha) fields in D..lPage Co., and
this
awears
to be a primary requirement.
3) Provide tall, dense grass cover.
Henslow's Sparrows typically are
fOUl'rl in areas where herabaceous vegetation is tall arrl. dense (Robins
1971a,b).
In my study Henlsow's Sparrows occupied areas with dense
vegetation >80 an high.
SUch vegetation can be obtained by using a variety
of grass species such as fescue, b:rane, arrl. orchard grass which will
provide frequent dense patches.
Maintenance of fields in the proper stages
91
of succession is inportant to Henslow' s Sparrows in the absence of natural
prairie (EadeS- ani 'Ihan 1981) .-m
4) Reduce woody encroadnnent.
'lhis should be done on areas where
Henslow's Sparrows are present or on lcu:ge fields with suitable habitat.
Henslow's Sparrows might use areas with widely scattered, low woody
vegetation, but they usually avoid areas where woody vegetation is
extensive ( Weins 1969, Birkenholz 1973, Kahl et al. 1985).
In
Missouri,
Kahl et al. ( 1985) fourx:l males used low woody vegetation for sin:Jin:J, but
avoided areas where woody vegetation was >1m high.
Few or no woody stems
were fourx:l arourrl song perches.
5) Avoid burning on areas where Henslow's Sparrows are present.
Burning is unfavorable for Henslow's Sparrows because it can prevent
nestin:J or delay it until
In Kansas, Knodel (1980)
cgx>sed
CCNer
is reestablished (Bowles arrl '!ham 1981).
fourx:l Henslow's Sparrows only on unburned sites as
to sites burned annually.
Becaus_e
they require a deep litter layer
for nest placement they will be negatively affected by frequent bums (Ryan
1986).
Grasshcg?er Sparrow
1) Maintain large fescue fields arrl reduce edge.
Samson (1980) listed
the Grasshq;p!r Sparrow as an area sensitive species requirin:J lcu:ge
grasslarrl tracts, usually >1 ha.
Nolin arrl Ritzenthaler (1987) found
:p:lSitive correlations bet.TNeen the rnnnber of pairs of Grasshopper Sparrows
arrl the distance to field edge in Ohio.
Johnson arrl 'I'enple (1986) found
the probability of oocurrence of a Grasshopper Sparrow's nest was higher in
lcu:ge prairie fragment arrl sanple plots located far fran a forest edge.
my study, Grasshopper Sparrows
were fourx:l exclusively in fields >16 ha.
In
92
'!he mnnber of Grasshaw& Sparrows arrl field size in the fescue habitat
2) Maintain fields in low bunchgrass, primarily fescue.
Fields of
bunchgrass are favorable to Grasshopper Sparrows for nestirg arrl foragirg
Whitnore (1981). Sodfonning grasses provide a mat of dense vegetation that
precludes effective foragirg.
Bunchgrasses ~eave openings or gaps that
allow the birds freedan to It¥JVe arourrl.
asscx::iated with bunches of grass.
Also nest placement usually is
Whi'boore (1981) fourxi nearly all nests
of Grasshopper Sparrow examined to be 3-walle:i, daned structures at the
bases of clUll'pS of grass. '!he largest mnnbers of birds located in my study
.
were fOUI'rl in fescue fields of short to medium height (45-80 em) •
3) Maintain grasslarrl in early succesional stages.
Whitnore (1981)
recxmnen::ied maintainirg grasslarrls in early successional stages with low
vegetation density, litter depth, arrl shrub cover.
Grasshopper Sparrows
will bree:i in distumed grasslarrl areas such as abarxloned cropfields
(Johnson arrl Odum 1956, Blakespoor 1980), arrl crop fields with sod residue
(Basol:euet al. 1986) •
~these
disttn:bed sites will suppoLL them,
cultivated grasslarrls generally hold denser pcp.tl.ations (Johnston arrl Odum
1956).
Bl1n'lin] seems to be an excellent choice for management of this type of
habitat.
But many authors criticize this management practice.
Knodel
(1980) fOUI'rl Grasshopper Sparrows m:>re c:x::mm::>n on 1.mburned prairie in
eastern Kansas.
In South Il:lkota, Forde et al. (1984) fOUI'rl decreased
mnnbers inmediately after a fire due to loss of nestirg
of insect food.
cover arrl reduction
In Montana, Bcx::k arrl Bcx::k (1987) detecte:i the species less
on areas that had been burned.
'!he scarcity of patches of taller
vegetation or perches makes these areas less suitable for Grasshopper
93
Sparrows.
Mowing can be suitable in creating this early suc:x:essional
~·
-Grassh~
nowed (Smith 1963).
Sparrows rarely abarrlon a field a:fterutt haS beetl
Grasshopper Sparrows increased substantially in Iowa
ilnmediately after cutting of alfalfa when the short CXNer they preferred
was provided (Frawley 1987) •
4) Reduce encroaching woody vegetation.
Grasshopper Sparrows
generally prefer areas with sparse or no woody growth.
In areas of
suitable habitat for Grasshq:per Sparrows, woody encroachment should be
minimized through bani reitOVal arrl possibly treatment with hert>icides.
Whitm:>:re (1981) recanmerrled burning grasslarrls with encroaching shrubs
during late winter to control woody vegetation arrl no planting shrubs or
trees.
Eastern Meadowlark
1) Provide perches.
Male Eastern Meadowlarks require sane erect
stru.ctures (e.g. woody vegetation, tall forbs, stakes, fenceposts,
t.elefi1one wiles,
al. 1980).
ete.) fer s::i:nqin:J ard observation (Bent 1958, DeGraaf et -
Ideal meada;lark habitat contains many perches.
'!he minimum
habitat area for Eastern Meadowlarks is 1.2 ha, with 4 perches/1.2 ha
(Schroeder arrl Sousa 1982).
Eastern Meadowlarks generally are adaptable in
selecting perches, usually choosing the highest perches within their
territories (Harrison 1977).
In high quality fescuejbluegrass areas, trail
markers <1 m tall served as excellent perches.
2) Maintain grasslarrls in short, dense vegetation, particularly fescue
or a fescuejbluegrass mixture with few forbs.
the fescue
I f01.ll'rl that large fields in
am mixed grass habitat types contained the
Meadowlarks.
IOOSt Eastern
Roseberry arrl Kilmstra (1970) f01.ll'rl birds preferred to nest
94
in pastures that -were planted
am then
~zed
to a 65% bluegrass
feseue mix-1 sintiiar to-the mixed grass habitat type- of my
Co., northem Illinois, Beecher (1942) fOlll'Xi that the
-study~
am 35%
· In Take
Eastern Meadowlark
was the only bird species for whidl bluegrass fields provided optinrum
corrlitions. Ti.Ioothy should not be planted in areas managed for Eastem
Meadowlarks.
Ti.Ioothy provided poor habitat for Eastem Meadowlarks because
it lacked enough cover
nesting habitat.
am litter at
grourd level to provide acceptable
Eastem Meadowlarks preferred areas of only a moderate
density of fortJs (<20%)
am generally avoided areas where fortJs
predaninant (Weins 1969, Sdlroeder
am
Sousa 1982) •
In
my
were
study, Eastem
Meadowlarks had <10% of their territories covered with fortJs.
3) Reduce encroaching woody vegetation.
Although Eastern Meadowlarks
use woody vegetation extensively for SOn:J p::sts, large percentages of woody
vegetation are generally urxiesirable.
Areas should contain <10% woody
cover interspersed throughout the field.
savannah
Sparrow
1) Maintain large fescue fields.
numbers
Graber
Fescue contained the greatest
am concentrations of savannah
am
Sparrows in
my
study.
In Illinois,
Graber (1963) fOlll'Xi highest JqW.ations in pastures with dense
grass cover, 10-25 em high with a continuous mat of vegetation.
grasses in these pastures -were fescue
am
Connnon
Kentucky bluegrass.
2) Manage grasslarrls with grasses of short to medium height, with
moderately dense cover.
requirements.
Fescue
am fescuejbluegrass fields meet these
Ti.Ioothy is urxiesirable, as it is too tall,
am does
not
95
provide suitable litter or dense cover near the grourxi.
am
Savannah Sparrows
Eastern Meadowlarks-~ similar hahltat.
3) Reduce encroac:hirg woody vegetation.
Although sane woody
vegetation is desirable for perches (sutton 1959), rn.nnerous woody stems
will discourage use of an area by Savannah Sparrows.
Woody
vegetation
should cover .:$10% of the grasslan::l.
Dickcissel
1) Maintain highly distu:r:bed fields with ab\.lmant foi:bs.
Dickcissels
generally prefer areas with dense cover of tall grasses an::l foi:bs.
Since
the Dickcissel is not aburrlant in DJPage Co. an::l sporadic in nost parts of
its range, managirg large annmts of this type of habitat might be
urxiesirable.
When
not used by Dickcissels, fields support only Red-wing'ed
Blackbirds an::l Son;J Sparrows.
Areas containirg this type of habitat should
be maintained, an::l areas where Dickcissels have bred consistantly in the
past should be protected.
2_)_ Plant primarily titoothy ani other tall grasses.
I fGUJ¥i
Dickcissels readily in ti.Ioothy which grows taller an::l provides denser cover
at greater heights than fescue or fescue/bluegrass mixtures.
Tim:>thy
is attractive breeciirg habitat for Dickcissels because it provides denser
cover an::l generally allows more species of foi:bs to invade (Zbmnerman
1971).
Red-winged Blackbird
1) leave sane areas idle.
Red-wirged Blackbirds require little
mailagement within the Forest Preserve District.
DlPage Co..
Generally habitat used by
Redw~
'lhey are ab\.lmant within
for nestirg is
96
un::lesirable for true grasslam birds.
Redwings are adaptable am can use
all-wetiam am-~lamflabitats tha't;;-are
J'leM
present.
'lhey witl -continue
to prosper as a by-product of management for other grasslarx:l birds, or by
the creation of marsh areas by the Forest Preserve District.
2) Maintain fields with dense grass arx:l fo:rbs.
Red-winged Blackbirds
generally are attracted to the tallest, densest vegetation within a given
field.
Fields of tim:>thy or other tall grass are generally I[K)re desirable
than fescue or fescuejbluegrass mixtures.
Tim:>thy provides tall, dense
cover that restricts visiblity arx:l allows numerous forb species to invade.
Tim:>thy is sturdy enough for placement of nests of Redwings.
Fescue arx:l
fescuejbluegrass are ususally too short arx:l not sturdy enough to provide
desirable cover.
Red-winged Blackbirds arx:l Dickcissels require vegetation
that supports their nests; they show sane similarilty in the placement of
their nests (Graber arx:l Graber 1963) •
'Ihe other 5 species examined during
lli:Y study require vegetation that provides cover for their nests.
3) Allow TNOOdy vegetation to invade a field.
is desirable for nest placement
am for fora.gincj
Short TNOOdy vegetation
(Shm't 1985} •
Bobolink
1) Maintain large, grassy open fields.
Bobolinks generally require
large expanses of grasslarx:l or forb cover (Weins 1969, DeGraff arx:l Rudis
1986).
Nolin arx:l Ritzenthaler (1987) fOlll'D positive correlations between
the size of fields arx:l the distance to the field edge arx:l the rn.nnber of
pairs of Bobolinks.
Beecher (1942) also noted that the Bobolink often
shtmned edge arx:l was fOlll'D only in open areas.
2) Maintain fields in no:ierately tall vegetation with dense groum
cover.
Bobolinks were fCJl.IOO in relatively equal rnnnbers throughout the 3
97
habitat types in Irr:f study.
Fields of fescue ani fescuejbluegrass mixtures
generally helcLthe-ltDSt birds.
H
TiJrothy fields--alse- centained -Bobotinks-but
not as many as several years earlier.
When these timothy fields were first
planted, ladino clover was planted also as a c:x:xrpanion crop.
provided dense grourrl cover for nestirg Bobolinks.
'!he clover
In recent years,
the
clover has disappeared leavirg the grourrl bare in many cases, ani opening
the areas to invasion of urrlesirable foms such as canada thistle.
3) Reduce encroachirg woody vegetation.
Although no reference could
be fourxl as to the affect of woody vegetation on Bobolinks, they did not
occupy fields with >10% woody cover in Irr:f study.

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