Flexibility in the face of climate change? A rapid and dramatic shift towards later spring migration in Hudsonian...

With rapid environmental change, shifts in migration timing are vitally important for population stability in migratory species and have been widely documented. However, little remains known about how migrants make these shifts and what factors influence the utilization of these strategies, limiting assessments of their vulnerability to climate change. Hudsonian godwits (Limosa haemastica) are extreme long-distance migratory shorebirds that (i) have previously advanced their population-level migration timing and (ii) are sexually dimorphic. We combined over a decade of tracking data from one breeding population with a historical predictive model to assess ongoing shifts in migration timing and investigate potential sex-specific migration strategies. We found that irrespective of sex, godwit departure and arrival timing shifted 6 days later from 2010 to 2023. The population maintained an average migratory duration of 24 days and drove shifts in arrival timing entirely by changing their non-breeding-ground departure. Yet, we also found godwits arrived later than predicted by the historical model, indicating that conditions on the non-breeding grounds may constrain their ability to respond to changes on the breeding grounds. These results emphasize the need for a more holistic approach to assessing the vulnerability of migratory species and the adaptiveness of changes in migration timing.