Automated telemetry reveals migratory movements and stopover timing of an endangered saltmarsh passerine

Abstract

Historically, the fates of individual passerines during migration have been informed primarily by scarce data on band recaptures and resighting. This constraint is particularly problematic for imperiled passerines because information on the timing and pathways of migration is not available to inform the development of effective actions necessary to reverse declines. We used automated telemetry stations to investigate the migratory ecology and movements of the globally endangered Saltmarsh Sparrow (Ammospiza caudacuta), for which the specifics of migratory behavior are poorly known. This short-distance migrant relies solely on coastal salt marshes in the eastern USA, breeding from Maine to Virginia, and migrating as far south as Florida. Saltmarsh Sparrows from different breeding (Maine, Massachusetts, and Rhode Island) and non-breeding (South Carolina and Georgia) latitudes generally followed similar migration routes, but individuals often had differences in departure dates. Movements were predominantly coastal, but detections suggest that sparrows also make inland and over-ocean migratory flights, particularly between southern New England and the mid-Atlantic. In fall, we detected multiple stopovers in coastal Connecticut, Rhode Island, and New Jersey, and identified spring stopover sites along the Delmarva Peninsula. Most fall stopovers lasted < 2 days, and stopover length decreased throughout the migratory season. Sustained migratory flights occurred only at night. More than 93% of migratory flights were associated with tailwinds at departure, and estimated flight ground speeds correlated weakly with tailwind support. Our research provides new understanding of migratory timing, pathways, and stopover use, which will inform actions such as land protection, marsh restoration, and the siting of near-shore wind development.