Nest predator abundance and urbanization

Abstract

We used infra-red triggered cameras, point counts, footprint monitors, and artificial nests baited with quail eggs to investigate the abundance of potential nest predators at 75 sites spread across a gradient of housing density in Franklin County, Tennessee. The total number of predators detected at each site showed a shallow positive rise with increasing housing density. Blue Jays (Cyanocitta cristata), domestic cats (Catus silvestris), raccoons (Procyon lotor), and opossums (Didelphis marsupialis) all increased in abundance, American Crows (Corvus brachyrhynchos) decreased in abundance, and the abundance of domestic dogs (Canis lamiliaris) was not related to housing density. Thus, in our study area, urbanization may increase populations of some nest predators, but not of others. The probability of predation on artificial nests containing a quail egg did not change with housing density, and quail egg predation was correlated only with the presence of raccoons and American Crows. These data suggest that quail eggs may not be an appropriate method for studying rates of predation on eggs or nestlings in urban settings, but may be helpful for assessing the abundance of American Crows and raccoons. More information is needed about how changes in the abundance of predators translates into changes in rates of predation on bird nests, and for studies of how urbanization affects populations of nest predators in regions other than North America and Europe. We also outline two parallel studies of economics and policy that may provide ways to connect conservation biology with changes in land-use planning.