Variation in Songbird Migratory Behavior Offers Clues About Adaptability to Environmental Change

For seasonally migrating birds, aspects of migratory behavior, such as the use of temperate versus tropical wintering areas, may influence their ability to respond to environmental change. Here, we infer potential flexibility in songbird migration from variation in two alternative stopover behaviors. Hierarchical Bayesian mark-recapture modeling was used to quantify stopover decisions over 19 years for four temperate and four tropical migratory species at a stopover site in southern Canada. Short-distance temperate migrants exhibited higher variability in behavior and greater responses to local weather than longer-distance tropical migrants, as measured by transience (the proportion of birds stopping <24 h, i.e. seeking brief sanctuary or subsequently relocating) and departure (re-initiation of migration by birds that stopped over for >24 h). In contrast to many previous works on climate-migration associations, annual variation in stopover behavior did not show strong links to broad-scale climatic fluctuations for either temperate or tropical migrants, nor was there any indication of directional changes in stopover behavior over the past two decades. In addition to suggesting that migratory songbirds-particularly tropical-wintering species-may face increasing threats with future climatic variability, our study highlights the potential importance of flexibility in en-route behavior for resilience to environmental change.