The Effects of Urban Sprawl on Birds at Multiple Levels of Biological Organization

Abstract

Urban sprawl affects the environment in myriad ways and at multiple levels of biological organization. In this paper I explore the effects of sprawl on native bird communities by comparing the occurrence of birds along gradients of urban land use in southwestern Ohio and northern California and by examining patterns at the individual, species, community, landscape, and continental levels. I do this by assessing the distribution and abundance of all bird species occupying sites of differing land-use intensity in Ohio and California. Additionally, I conducted predation experiments using artificial nests, tracked the nest fate of American Robins and Northern Cardinals, and assessed land cover in these sites. At the individual level, predation on artificial nests decreased with urbanization; however, this trend was not reflected in the nesting success of robins and cardinals, which did not increase with urbanization. At the species level, sprawl affected local patterns of extinction and invasion; the density of different species peaked at different levels of urbanization. At the community level, species richness and diversity peaked at moderate levels of urbanization, and the number of low-nesting species and of species with multiple broods increased with urbanization. The community-level results may reflect both the species-level patterns of local extinction and invasion as well as broader landscape-level patterns. At the landscape level, a linear combination of spatial heterogeneity and density of woody patches accurately predicted both species richness and Shannon Diversity. At the continental level, local extinction of endemic species, followed by the invasion of ubiquitous weedy species, leads to faunal homogenization between ecoregions.