Stopover ecology of fall migrating landbirds at an inland stopover site in northeastern Pennsylvania dominated by nonnative vegetation

Abstract

Landbirds are especially vulnerable during migration as they move through novel habitats and encounter enhanced predation risk, unpredictable food resources, enhanced competition, and inclement weather. Further, numerous studies suggest exotic vegetation species have the potential to alter habitat quality, in turn affecting the fitness of migratory birds. The purpose of this study was to evaluate fitness correlates associated with fall migrant use of shrubland habitat dominated by nonnative honeysuckle (Lonicera spp.) in northeastern Pennsylvania. Additionally, we looked for differences in stopover ecology between demographic cohorts (age, and in the case of Common Yellowthroat [Geothlypis trichas], both age and sex). We used estimates of mass change as our primary fitness indicator, assuming that evidence of positive mass change reflects fat deposition and hence indicates quality habitat. Our results suggest that of 7 species, 1 gained mass, 5 neither gained nor lost mass, and 1 lost mass. Further, while we found little evidence of age or sex differences in migratory timing, we did find evidence that older birds gained mass at a higher rate than younger in 2 species and that, while male Common Yellowthroats maintained mass while using our site, females lost mass. We conclude that our exotic-dominated shrubland habitat does not provide high-quality stopover habitat for most species.