Subarctic‐breeding passerines exhibit phenological resilience to extreme spring conditions

Abstract

AbstractThere has been relatively little study of the capacity of subarctic passerines to adjust their phenologies to rapid changes on their breeding grounds. Here, we assess variation in passerine arrival timing in Denali National Park, Alaska, from 1995 to 2015, a period that included both the warmest and coldest recorded mean spring temperatures for the park. Using an open‐population occupancy modeling approach in which arrival events are random variables, we investigated interannual variation in the arrival distribution for 10 Nearctic–Nearctic migrants, three Nearctic–Neotropical migrants, and one Palearctic migrant. Neotropical–Nearctic migrants varied in terms of the flexibility of their arrival timing, but generally showed plastic phenologies, suggesting resilience under extreme spring conditions. In comparison, Nearctic–Nearctic migrants showed similar or greater plasticity in arrival timing. A majority of species showed synchronous–asynchronous fluctuation in arrival (i.e., synchronous arrival in some years, asynchronous in others) in combination with various levels of the mean response (i.e., early, average, and late arrival), suggesting the presence of interactions between environmental conditions at multiple scales and inter‐individual variation. The presence of synchronous–asynchronous fluctuation in arrival suggests that weakening of the north–south temperature gradient under continued Arctic amplification may strongly affect arrival variances. Our results also suggest that complex interactions between distributional and phenological changes may be possible. For example, the arrival distribution of Fox Sparrow (Passerella iliaca) became more synchronized over time, a pattern that coincided with a dramatic increase in occupancy probability through expansion of its elevational distribution. Overall, our findings suggest that monitoring of the mean–variance relationship may lead to a deeper understanding of the factors shaping phenological responses.