Gulls can change their migratory behavior during lifetime

Abstract

Migration is a widespread phenomenon among birds and is likely to be subject to strong selective pressures. Birds' annual routines and behaviors might be expected to change during their different life history stages, resulting in different, age‐related migration patterns. However, although migration has been the subject of many publications, age‐related differences in migration have received little attention. The present study examined age‐related changes in individual migration habits in lesser black‐backed gulls, Larus fuscus . We analyzed data from 10‐year (1998–2007) color‐ringing project in NW England, comprising more than 10 000 ringed individuals. Our results showed a latitudinal cline in age structure across the wintering range, with adults and gulls in their first breeding year wintering closer to the breeding grounds. Supporting this result we observed that individuals, as they get older, changed the migration behavior and winter closer to the breeding areas. Interestingly, we found no differences in survival rates across the wintering grounds. Thus differences in survival rates can not account for the latitudinal cline in age structure, and the observed findings seem to be best explained by the arrival time hypothesis, based on a mechanism whereby individuals are able to change their migratory behavior as result of the onset of sexual maturity and associated mating pressures.