Delayed autumn migration in northern European waterfowl

Abstract

Climate change is causing phenological shifts in the environment. Among birds, increasing temperatures have been shown to advance the spring migration and breeding, which in turn affect individual reproductive success. The autumn migration phenology has, however, been largely overlooked. Here, we study long-term changes in the timing of autumn migration in 15 northern European waterfowl species during 1979–2009. We hypothesised that waterfowl should delay their migration since they winter north of the Sahara desert. Our results show that 6 (Greylag Goose Anser anser, Eurasian Wigeon Anas penelope, Eurasian Teal Anas crecca, Tufted Duck Aythya fuligula, Velvet Scoter Melanitta fusca, and Common Goldeneye Bucephala clangula) of the 15 studied species have delayed at least one of the three phases of migration examined. The most marked delay in median migration dates was by more than a month over the past 31 years. Only the Bean Goose Anser fabalis exhibited an advanced beginning of its migration. We also analyse the timing of the entire waterfowl migration and show that the median and end of the migration have been significantly delayed. The results support our predictions and highlight how rapid phenological responses to climate change may be. Such delayed departures may be the cause for recently observed northward shifts of wintering ducks. Our results suggest that waterfowl to be a good indicator group for climate change. Changing migration times can also have population-level consequences due to differential hunting and natural predation pressures over the waterfowl flyway.