The ecology of birds in the urban landscape: Avian community composition, dispersal, and survival across the rural-to-urban gradient in Washington D.C

Urbanization during the latter half of the twentieth century has altered habitats, restructured wildlife communities, and influenced the range sizes and population dynamics of animal species. While many bird species persist in urban environments, little is known about the consequence of urbanization on birds -- in part because urban landscapes confer conflicting pressures, such as exposure to novel predators, and benefits, such as anthropogenic food resources. Here, we explore the influence of urbanization on birds in the Washington D.C. metropolitan area using a unique study design that addresses the community composition, dispersal behavior, and survival of birds across the rural-to-urban gradient within the context of a regional citizen science project. We found supportive evidence for environmental filtering of bird communities by assessing variation in functional diversity as well as the proportional and apparent abundance of avian life history guilds within sites across the rural-to-urban gradient. To address the influence of urbanization on avian dispersal, we explored the degree of permeability of habitats in association with the spatial distribution of four species of birds banded and reencountered in subsequent years. There was supportive evidence that, for two of the four species, the distribution of habitat influences settlement patterns of birds and thus shapes dispersal behavior in human-dominated landscapes. Finally, we used mark-recapture data to assess variation in adult survival across the rural-to-urban gradient to test hypotheses about the processes by which urbanization is expected to influence avian survival. Adult survival was enhanced in suburban and urban habitats for four of our seven focal species and there was no evidence in support of an influence of urban land cover on survival for the remaining species. Taken cumulatively, this research addresses three distinct ecological relationships between birds and their environments and provides a significant advancement in our understanding of the influence of urbanization on wildlife populations.