Habitat selection, movement, and activity budgets of neotropical landbird migrants following trans-Gulf migration

David Asher Aborn


Habitat selection is very important to the evolution and ecology of organisms. For migratory birds, habitat selection is complicated by the fact that the birds encounter a wide diversity of habitats on their breeding grounds, wintering grounds, and especially during migration. Selection of the proper habitat at migratory stopover sites is critical, as it can mean the difference between survival and reproduction, or becoming a casualty of migration, the very phenomenon that has enabled many avian species to persist. Despite its importance, little research has been conducted on habitat selection during migration, especially the proximate mechanisms of this behavior. I investigated the process of habitat selection at a Gulf coast stopover site. I radiotracked Summer Tanagers (Piranga rubra) on a Gulf coast barrier island following spring trans-Gulf migration. The results suggest that tanagers explore the available habitats prior to settling, rather than use prior information or innate preferences. Sex, age, and energetic condition all influenced habitat use and movements, with energetic condition producing the most notable differences. Birds spent the greatest proportion of their time perched, with 5% or less of their time spent foraging. Again, sex, age, and energetic condition influenced activity budgets. Mist-netting data from eleven species of migrants revealed that leaner birds tended to use a greater number of habitats, and either gain more or lose less mass than individuals using only one habitat. There were differences in the relative suitability among habitats, but migrants exhibited no differences in the pattern or rates of movement among habitats, suggesting that they were treating the habitats equally. The netting data suggest that leaner migrants might be switching habitats as the suitability of a given habitat patch decreases, thereby improving the chances of depositing fat and resuming migration in a timely manner. Taken together, the telemetry and netting data reenforce the importance of habitat diversity in the conservation of migratory landbirds.