Storm-induced mass mortality results in both immediate and long-term consequences for a migratory songbird.

Extreme weather events are occurring more often, resulting in increasingly frequent mass mortality events for plants and animals. Identifying why individuals die during these events and their long-term consequences for populations can enable a mechanistic understanding of species' vulnerability to global change. Here we report on early-arriving purple martins (Progne subis)-a migratory songbird-that were killed at >50% of their breeding sites across two US states during a severe winter storm event in 2021. Victims exhibited substantial allelic differences from individuals sampled before and after the storm event. The surviving population suffered delayed breeding, reproductive failure and, in 2022, late breeding-ground arrival. Phenological trait values returned to the mean by 2024, yet the population may be unlikely to recover demographically until at least 2027. Purple martins are markedly declining in the region and signatures of past events suggest that frequent mass mortality events may be challenging their resiliency.