The spatial impact of an urban area on breeding birds

Urbanization alters the landscape profoundly affecting plant and animal distributions and abundances. Urbanized areas negatively affect bird communities by favoring resident generalist or invasive species, in turn, reducing diversity and promoting local extinction. Even though urbanization affects biodiversity in many systems, the spatial extent to which a metropolitan area impacts biodiversity is not well characterized. The goal of the present study was to elucidate the areal extent to which an urban/suburban landscape affects avian diversity. I conducted a breeding-bird distribution study containing over 2,000 roadside survey locations in a 500,000 ha study area in north-central Tennessee, that contained areas of natural and urban (mainly the city of Nashville) land cover. Breeding bird species were divided into three guilds: those that breed and winter in the same area-residents; those that breed and winter in different but relatively close areas-short-distance migrants; and those that breed in North America and winter in Central and South America-Neotropical migrants. These data were spatially analyzed through spatial interpolation surface models: Kriging and linear surface models. Neotropical migrant richness exhibited stronger negative associations with urban land cover than either residents or short-distance migrants. The surface model for urban land cover formed urban density zones. Neotropical migrant total richness spatial patterns significantly corresponded to the urban spatial patterns. Neotropical migrant breeding bird richness was significantly less over a 150,000 ha area of urban/suburban-developed landscape, or an area 50 times larger than Nashville's downtown district. Assessment of the overall metropolitan spatial effect to diversity will provide a benchmark for areal urban/suburban impacts that can assist conservation and management strategies directed towards controlling environmental impacts of urban sprawl.