EDGE AVOIDANCE BY NESTING GRASSLAND BIRDS: A FUTILE STRATEGY IN A FRAGMENTED LANDSCAPE

Some grassland passerine species are considered area-sensitive, but the mechanisms underlying that phenomenon are not understood, particularly on grazed grasslands. Area sensitivity may result from edge avoidance or higher nest predation near edges, both of which may be influenced by predator activity or cattle-induced vegetational differences between pasture edge and interior. We assessed the effect of distance to edge on nest density and predation Savannah Sparrows (Passerculus sandwichensis), Grasshopper Sparrows (Ammodramus savannarum), Bobolinks (Dolichonyx oryzivorus), and meadowlarks (Sturnella spp.) along wooded and nonwooded edges of Wisconsin pastures in 1998-2000 and the activity of potential mammalian nest predators along those edges in 2000-2001. We found a positive relationship between nest density and distance from edge for all edge types combined, but that was not the result of effects of wooded edges: we found no difference in density between nests located