Tree Swallows (Tachycineta bicolor) are migratory aerial insectivores that breed across North America and have experienced long-term population declines. Although the mechanisms behind these declines have proved difficult to identify, emerging methods for studying migration staging areas could provide new insights. Tree Swallows congregate in staging roosts during fall migration, gathering at sunset to roost overnight, then leaving at sunrise to feed or continue their migration south. Using a particularly large roost site in Connecticut, USA, we used NEXRAD Level III data to calculate metrics of reflectivity corresponding to snapshots of morning roost size each day. Using these metrics as measures of relative abundance, we tested predictions about the effects of wind and date on daily roost size and day-to-day changes in relative abundance. We found that radar reflectivity around the roost decreased with higher wind speeds during the morning emergence and when wind speeds were high the previous day. In addition, we found a temporal pattern of roost abundance corresponding to a peak of migration around the end of August for this stopover site. Our results provide insight into the sensitivity of Tree Swallow responses to wind conditions and lay the groundwork for future studies using NEXRAD to examine links between migratory behavior and declines in swallow populations.

You do not currently have access to this content.