Adult male birds advance spring migratory phenology faster than females and juveniles across North America

Abstract

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 Americacomprising 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, 95 CrI = −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.

Why sex matters in phenological research

“…Notably, when one insect species is excluded, five species with sex dissimilarity indicated that reproductive phenology of males was more variable than that of females (three birds, Gordo et al 2013, Harnos et al 2015, Hedlund et al 2015; two amphibians, Chadwick et al 2006). This pattern accords well with a recent finding that males are more likely to advance their breeding migration phenology than females across 36 bird species (Neate‐Clegg and Tingley 2023). Although data are very limited, this pattern clearly contrasts with the conventional view that females are more likely to shift reproductive phenology than males (Ball and Ketterson 2008, Chmura et al 2020).…”

“…courtship and breeding migration), which should be assessed in the context of sexual match/mismatch hypothesis. Indeed, a recent study has shown that males are more likely to advance their breeding migration phenology than females across 36 bird species (Neate‐Clegg and Tingley 2023), which contradicts the conventional view that females should exhibit more plastic responses to climate change (Ball and Ketterson 2008, Chmura et al 2020). Overall, although climate change‐induced phenological shifts are likely sex‐specific, many questions remain such as which sex is more likely to shift phenology under climate change, what determines it, and how sex‐specific phenological shifts can mediate seasonal population dynamics and long‐term demographic trends.…”

Sexes in sync: phenotypic plasticity, sexual selection and phenological synchrony between the sexes in a wild hibernator

“…The uncoupling of community interactions as a result of asynchronous phenological responses to climate change has been raised as a conservation concern [2,51–53]. Lane et al .…”

“…The uncoupling of community interactions as a result of asynchronous phenological responses to climate change has been raised as a conservation concern [2,[51][52][53]. Lane et al [19] found that female Columbian ground squirrels plastically delay emergence from hibernation in response to delayed snowmelt, but a lack of similar information on males has prevented an understanding of potential desynchrony between the sexes.…”

Thermal microrefugia and changing climate affect migratory phenology of a thermally constrained marine mammal

“…For example, as migratory bird species shift to earlier breeding and nesting dates, they exhibit mismatched timing to peak vegetation and associated insect biomass, reducing prey availability (Visser and Both, 2005;Moore, 2011;Mayor et al, 2017). Conversely, similar species or populations of the same species have not changed the timing of their migration and nesting activities in the face of climate change, illustrating that populations or individuals within the same or similar species may react differently to changing climate conditions (Visser and Both, 2005;Moore, 2011;Neate-Clegg and Tingley, 2022). Other species of birds and insects have ceased migrations in recent years and instead remain year-round at midlatitude sites that were previously used as stop-over locations (Groepper et al, 2008;Pulito and Berthold, 2010;Moore, 2011;Satterfield et al, 2018).…”