The conservation value of urban riparian areas for landbirds during spring migration: Land cover, scale, and vegetation effects

Urbanization changes bird community structure during the breeding season but little is known about its effects on migrating birds. We examined patterns of habitat use by birds at the local and landscape level during 2002 spring migration at 71 riparian plots along an urban gradient in Cincinnati, Ohio, USA. Using linear regression, we examined variation in relative density, species richness, and evenness of four migratory guilds associated with natural land covers and building area at four scales (50, 100, 250, 500 m radial buffers). We also examined the influence of local vegetation using multiple regression models. As building area increased, riparian forests tended to be narrower and have fewer native trees and shrubs. In general, native birds were positively associated with tree cover (within 250-500 m of stream) and native vegetation, and negatively with building area (within 250 m); exotic species responded inversely to these measures. Short-distance migrants and permanent residents displayed the weakest responses to landscape and vegetation measures. Neotropical migrants responded strongest to landscape and vegetation measures and were positively correlated with areas of wide riparian forests and less development (>250 m). Resident Neotropical migrants increased with wider riparian forests (>500 m) without buildings, while en-route migrants utilized areas having a wide buffer of tree cover (250-500 m) regardless of buildings; both were positively associated with native vegetation composition and mature trees. Consequently, developed areas incorporating high native tree cover are important for conserving Neotropical migrants during stopover.