Mass Change Values of Landbird Migrants at an Inland Stopover Site Dominated by Nonnative Vegetation

Early successional habitats are declining in eastern North America while at the same time remaining habitats are being invaded by a suite of nonnative shrub species. While the significance of these transitional habitats to breeding birds is well known, increasing evidence suggests they are important during the postfledging/premigratory and migratory periods, not only for shrub-nesting species but also for many species that breed in late-successional habitats. Additionally a number of studies suggest exotic species have the potential to alter habitat quality, in turn affecting the fitness of migratory landbirds. The purpose of this study was to evaluate fitness correlates associated with migrant use of shrubland habitat dominated by nonnative honeysuckle ";Lonicera spp." in order to gauge habitat quality for spring migrants using an inland stopover site in northeastern Pennsylvania. We used estimates of mass change as our fitness indicator, with positive mass change indicating quality habitat. Our results suggest most birds gain mass while using honeysuckle-dominated habitat and many species, including species that characteristically breed in forested habitats, accrue fitness advantages from using shrubland habitat during spring stopover in northeastern Pennsylvania. However, we emphasize the need to examine the cumulative effects of exotic vegetation through multiple stages of the avian annual cycle to better understand the fitness consequences of nonnative vegetation on migratory landbirds.