Abundance, Habitat Selection, and Food Habits of Grassland Birds in 3 Non-Native Grasslands in Northern Illinois

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, 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.