Abundance, Habitat Selection, and Food Habits of Grassland Birds in 3 Non-Native Grasslands in Northern Illinois
File(s)
Date
1990-08Author
Kobal, Scott N.
Publisher
University of Wisconsin-Stevens Point, College of Natural Resources
Metadata
Show full item recordAbstract
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, grass/forb)
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, P<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 (P<0.05) in the
grass/forb fields. Fescue was the only habitat type in which a
correlation (P<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 (P<0.05)
with bird density in spring. Insect composition differed between
the 3 habitat types. The largest number of insects captured was
in the fescue habitat type. The greatest concentration of insect
orders (Orthoptera, Coleoptera, and Lepidoptera) most often
selected by all bird species was in the grass/forbs 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.