Extensive post-breeding movements of Adriatic Yellow-legged Gulls Larus michahellis

Abstract

The Yellow-legged Gull Larus michahellis is generally considered to be sedentary and dispersive, with long-distance dispersal of young birds developing after the 1970s. In this paper, we present the analysis of the movement of the Yellow-legged Gulls from the eastern Adriatic coast based on observations of colour-ringed birds marked between 1999 and 2011. A total of 4,114 sightings of 1,559 Yellow-legged Gulls marked as chicks were analysed. Our results showed a clear preference in the direction of the movement of Yellow-legged Gulls and significant differences in the directions of movements and the longitude of the observation sites of birds from different colonies. During summer and autumn, the majority of gulls moved towards the north, to the Baltic and North Sea coasts. Maximum distances covered (1,958 km for juveniles and 1,380 km for adults) were much greater than for the other studied populations of the Yellow-legged Gull. We found no difference between the directions of the movement among age classes, while distances decreased with age. Three important features: long-distance movements, migratoriness of adults and differences in movements between colonies, do not support the theory that post-breeding movements of the Yellow-legged Gull have been recently developed as the result of population increase. We presume that the recent pattern of movements reflects the evolutionary history of the Yellow-legged Gulls and might be inherited or result from experience and have been transferred by learning between generations among birds from the same colony.