Nesting habitat and responses to habitat edges of three grassland passerine species.

Abstract

Grassland passerines breeding in tallgrass prairie may have particular nest microhabitat affinities within nest sites and have different habitat affinities at nest sites among species. In Chapter 1, I examined nest sites of three passerine species--eastern meadowlark (Sturnella magna), dickcissel (Spiza americana), and grasshopper sparrow (Ammodramus savannarum)--in east central Kansas tallgrass prairie. I tested for nest microhabitat (0.25 m2 around nests) characteristics within species and compared nest microhabitats and habitats in larger areas around nests (1-to lO-m radii) among species. Nest microhabitats of all species had less bare ground cover than larger areas around nests, while only dickcissel and grasshopper sparrow nest microhabitats had significantly greater (P < 0.05) vegetation variable means than larger areas around their nests. Several habitat characteristics were found to be significantly different among the nest sites ofthe three species at both spatial scales measured. My findings support previous nest-site habitat descriptions and abundance-habitat correlations for these species. Different habitat edge types may have differing effects on breeding grassland birds in fragmented tallgrass prairie. In Chapter 2, I compared nest predation, brood parasitism by brown-headed cowbird (Molothrus ater), and nest placement of the three study species in relation to their nest distances from woodland and agricultural edges in east central Kansas tallgrass prairie. Daily nest survival rates of the three species were not significantly (P > 0.05) influenced by nest distances in relation to either edge type, and only eastern meadowlark experienced significantly (P < 0.05) higher brood parasitism rates :s 100 m of woodland edges. Dickcissel nested farther from woodland edges than agricultural edges and grasshopper sparrow nested farther from agricultural edges relative to the nest placement of the other study species. My findings suggested possible influences of woodland edges on brood parasitism and of both edges on the nest-site selection of certain grassland passerine species within 100 m of habitat edges.