Influence of Patch and Landscape Characteristics on Grassland Passerine Density, Nest Success and Predators in Southwestern Wisconsin Pastures;Doctoral thesis

摘要

Fragmentation of grasslands has been implicated in grassland bird population declines, based on assumptions that pattems of species presence, density, and productivity are influenced by patch and landscape characteristics. Although birds are likely selecting habitat at several scales, few studies have compared the relative importance of factors at different scales to these pattems. Furthermore, studies evaluating area sensitivity have not accounted for other hypotheses that, if true, can result in a positive correlation between patch size and species presence. We evaluated the relative importance of characteristics at three scales (within-patch, patch, and landscape) to patterns in density of Savannah sparrow (Passerculus sandwichensis), grasshopper sparrow (Ammodramus savannarum), eastern meadowlark (Sturnella magna), and bobolink (Dolichonyx oryzivorus). We surveyed birds in 74 southwestern Wisconsin pastures from 1997-1999 and used Akaike Information Criteria to select the best vegetation, patch/landscape, and vegetation/patch/landscape models of density for each species. We also evaluated area sensitivity for each species while accounting for three hypotheses that can lead to false conclusions that area sensitivity is occurring.