Advances in spring migratory phenology comprise some of the most well-documented evidence for the impacts of climate change on birds. Nevertheless, surprisingly little research has investigated whether birds are shifting their migratory phenology equally across sex and age classes – a question critical to understanding the potential for trophic mismatch. We used 60-years of bird banding data across North America – comprising over 4 million captures in total – to investigate both spring and fall migratory phenology for a total of 98 bird species across sex and age classes, with the exact numbers of species for each analysis depending on season-specific data availability. Consistent with protandry, in spring (n=89 species), adult males were the first to arrive and immature females were the last to arrive. In fall (n=98), there was little difference between sexes, but adults tended to depart earlier than juveniles. Over 60 years, adult males advanced their phenology the fastest (-0.84 days per decade, 95CrI = -1.22 to -0.47, n=36), while adult and immature females advanced at a slower pace, causing the gap in male and female arrival times to widen over time. In the fall, there was no overall trend in phenology by age or sex (n=57), driven in part by high interspecific variation related to breeding and molt strategies. Our results indicate consistent and predictable age- and sex-based differences in the rates at which species’ springtime phenology is shifting. The growing gap between male and female migratory arrival indicates sex-based plasticity in adaptation to climate change that has strong potential to negatively impact current and future population trends.

See Methods of Neate-Clegg & Tingley, Global Change Biology. Briefly, raw banding data were extracted from the USGS Bird Banding Lab. A series of stringent filters were applied to narrow the dataset down to meet sample size requirements. Then, Weibull-corrected phenological metrics were calculated for every age group and sex for every species.