Habitat interactions structuring songbird communities across forest-urban edges

Urban habitats vary greatly in the resources they provide for birds and other wildlife. Few species entirely avoid either human or forest habitats and for species that regularly utilize both, the two habitat types (forest and urban) may interact in complex ways to shape the animal communities at the forest-urban ecotone. I studied habitat relations to songbird community structure across the urban-forest edge in a heavily urbanized watershed in the New York metropolitan region. My research was designed to provide specific knowledge about the natural and human-built habitat components that maintain avian richness and abundance. I found that mature, intact forests with large trees and greater vertical complexity were the most valuable to birds breeding in and migrating through urban forests. Also, shrubby habitats along forest edges bolstered bird richness because they provide habitat for specialized shrub-nesting species. In my study, urban forests of a broad range of sizes and habitat conditions were associated with increased bird diversity in adjacent human habitats up to at least 0.2 Km from their edges. A high density of large trees in the urban matrix was related to increased avian richness outside the forest in urban neighborhoods. Also, a high density of large trees in the urban matrix was associated with higher richness and abundance of breeding and migrating birds inside adjacent forests. Because residential areas have the highest density as well as variety of large trees relative to other types of urban land use, they also contain the greatest richness of birds. This study demonstrates that local habitat is very important in structuring the bird community both inside forests as well as in the urban matrix but adjacent habitat also affects bird community structure. Forest area and isolation are relatively unimportant in shaping bird communities at the forest-urban ecotone. These findings suggest a wide-range of conservation practices, including forest preservation, management of shrubby edges, and planting and caring for a variety of long-lived trees in urban neighborhoods, that would maintain a rich bird community in urban regions.