Migration and Carry-Over Effects in Tree Swallows (Tachycineta bicolor)

Abstract

There is growing evidence of carry-over effects in migratory birds. Aerial insectivores are declining across North America; therefore, to determine the cause of these declines, we must have a holistic view of their annual cycle. I use geolocators to map the annual movements of tree swallows breeding in Nova Scotia, Canada, determine if reproduction has carry-over effects on migration, and examine the effects of geolocators. Geolocators revealed that tree swallows began migration in July and had an extended stopover in the northeastern United States. They wintered in Florida or Cuba, returning from spring migration in late April. This study revealed that later breeding swallows began migration later than earlier breeding swallows, but all birds arrived on the wintering grounds around the same time, due to differences in stopover length. No short-term effects of geolocators were found, although the sample size was small, and thus these results must be interpreted cautiously.