Derric Pennington, University of Minnesota and Robert Blair, University of Minnesota.
Background/Question/Methods Urban areas can harbor a diversity of breeding birds, but the relative importance of proximate vegetation and landscape factors that influence their distribution in a city are poorly understood. We examined breeding riparian bird communities and the influences of two important biophysical features of the urban environment – vegetation and buildings. To better understand the relative importance of landscape features at different spatial scales within an urban landscape, we surveyed breeding songbirds and a number of vegetation characteristics on 71 sites along an urban gradient within Cincinnati, Ohio, U.S.A. Landscape features at larger scales were quantified using GIS. We took a functional-group approach to examine the bird communities in order to ascertain potential mechanisms. Using an information-theoretic approach, we modeled relative density, species richness, and evenness in relation to local woody vegetation and to tree cover, grass cover, and building density within 50-1000 m of each site.
Results/Conclusions In general, models containing both proximate woody vegetation and landscape factors were most important in explaining bird density and diversity. Native canopy and understory woody measures were the most important vegetation measures – positively associated with native, Neotropical migrant, insectivorous, single brood, upper canopy, and open-cup nest building species while exotic, short-distance migrants, omnivores, multi-brood, ground nesting species responded oppositely. At the landscape scale, both tree cover and grass cover were the most important factors across guilds; tree cover was positively associated with permanent residents, aerial feeders, and single-brood species, and negatively with omnivorous and exotic species while grass cover was positively associated with several guilds, including multi-brood and ground foraging species. Building density was most important and positively influenced exotic, granivores, and cavity-nesting species and negatively influenced Neotropical migrant, single-brood, upper-canopy feeding, open-cup nesting species. Bird community responses to spatial scale varied; in general, smaller spatial scales (< 500 m) best described bird density while richness was best described by larger scales (> 500 m). Overall, native breeding birds in urban areas would be served well by management practices that maintain a wide buffer of native vegetation around urban streams.