Two-sided edge responses of avian communities in an urban landscape

Impacts of habitat edges on wildlife populations have received considerable attention, yet few researchers have quantified changes in animal community structure on both sides of an interface between distinct habitats. To gain a better understanding of the ways in which species-specific responses scale up to produce community patterns across habitat boundaries, we examined the response of avian communities to forest-suburb edges in northeastern Illinois, USA. We surveyed bird assemblages using replicated point-transects (n = 21) that crossed boundaries between remnant forest patches and suburban residential areas in order to compare differences in community composition, species distributions, and densities. Forest and suburban bird communities were distinct, and community composition changed with distance-from-edge in forests but not suburbs. Abundances of many species that were common in the forest increased with distance-from-edge in the forest, whereas numbers of common species in the suburbs were largely unaffected by distance-from-edge. Using a new metric that we termed “tolerance,” we found many forest species avoided the edge and suburbs, and suburban species were present near the edge but did not venture far into forest. Overall, distance to the forest-suburb boundary was more influential in structuring avian communities in the forest. Some species of conservation concern crossed edges into the suburbs, suggesting that management activities may improve suburban biodiversity. Many other imperiled forest species, however, will only be retained in urban environments through the protection of forest interior habitat.