Migratory behavior and connectivity revealed in a secretive Neotropical migratory songbird, the Swainson's Warbler

Improving our understanding of migratory behaviors and connectivity is fundamental for identifying limiting factors and drivers of population decline. With advances in miniaturized tracking technology, we are now able to study these critical aspects of avian ecology, which, for secretive species, was once an exceptional challenge. Here, we identify several unknown aspects of the migratory behavior and connectivity of the elusive Swainson's Warbler (Limnothlypis swainsonii), by tracking individuals from populations breeding in Louisiana, U.S., and wintering in Jamaica. We identified a migratory divide between the western and eastern portions of the species' distribution, showing that most Louisiana breeders overwintered in southern Mexico and the Yucatan peninsula, whereas the Jamaica individuals migrated to the eastern portion of the Swainson's Warbler breeding range. Geolocator data documented that a portion of migratory flights in both populations were sustained well into the day, suggesting that birds migrated over large bodies of water (i.e., Gulf of Mexico and Caribbean Sea) during both spring and fall migration. Furthermore, the phenology and rate of migration differed between populations. Additional research efforts across a broader portion of the range are necessary to better understand the demographic consequences of high migratory connectivity and the implications for the conservation of the species.