Inland flights of young red-eyed vireos Vireo olivaceus in relation to survival and habitat in a coastal stopover landscape
Bradley K. Woodworth, Charles M. Francis, Philip D. Taylor
Inland dispersal of migrating land birds away from the coast, often opposite to the direction of migration, occurs frequently. Many of these movements may involve migrants seeking improved stopover conditions farther inland, but direct study of inland flights and of the ecological factors influencing their occurrence is limited. We used an automated telemetry array and ground-tracking to assess flight behaviours, survival, and habitat use of young red-eyed vireos Vireo olivaceus during fall migration at a coastal island and an inland stopover site in southwest Nova Scotia. We recorded inland flights for 41% (11/27) of individuals that departed the island. At least 25% of 16 individuals tagged at the inland site also relocated within the landscape prior to continuing migration, but due to the higher proportion of ambiguous flights at the inland site (44%) compared to the island (15%), we could not be sure if actual proportions of relocations differed between sites. Mortality on the island (at least 10 of 39 individuals) was significantly higher than at the inland site (0 of 16 individuals). At mainland sites near the coast where we found 6 of 11 individuals after they relocated away from the island, mortality remained high (2/6). Lack of deciduous canopy cover may have contributed to the high mortality on the island, but coastal mainland sites had a relatively high amount of deciduous canopy cover, similar to at the inland site where there was no mortality. Although coastal stopover sites may be important for migrating songbirds, especially before or after making a large water crossing, our results show that mortality can be much higher, and habitat poorer, at the coast compared to farther inland. Therefore, relocating inland may be an adaptive strategy for individuals that initially settle at the coast and that need to rest and refuel before they continue migration.