Migratory behaviour constrains the phenological response of birds to climate change

Migratory birds may be unable to respond to climate change at their breeding grounds in the same way as residents because they do not experience local environmental conditions until migration has been completed, or because of limited plasticity in response to environmental variation. Indeed, several studies have shown that long-distance migrants have advanced their phenology less than short-distance migrants in recent decades, suggesting a slower phenological response to ongoing climate warming. However, few studies compared the phenological response of species that live year-round within the same climatic region (including residents) with that of species migrating over longer distances. We used an extensive data set on temporal change in spring first singing date (FSD) during 1977-2006 of 56 resident and migratory bird species in Northern Germany to test whether migratory status affected 2 aspects of the phenological response: the temporal trend in FSD and the response of FSD to local temperatures. Species migrating <4 degrees latitude (ca. 450 km) (less migratory species) showed greater temporal advancement in FSD compared to more migratory species. In addition, the variance in temporal trends was larger among less migratory species. Higher local temperatures were associated with earlier FSD, and multi-brooded species showed a stronger advancement in FSD with higher temperatures than single-brooded species. However, the temperature response was unaffected by migratory status, suggesting that the difference in the temporal trend in FSD between less migratory and more migratory species was mainly due to climatic and/or environmental cues regulating departure of the latter from the wintering areas and/or temporal scheduling of migratory flights, rather than to differential responses of FSD to local temperatures. Therefore, migratory behaviour should be regarded as a life-history trait possibly constraining the phenological response to rapid climatic changes in avian species.