The origin of Lesser Black-backed Gulls Larus fus- cus wintering in central Iberia

The origin and age of Lesser Black-backed Gulls Larus fuscus wintering inland on the Iberian Peninsula were mapped using sightings of colour-ringed birds. A total of 288 individuals were sighted over a 17 year period. The gulls originated from seven different countries, with the majority being ringed in the United Kingdom and the Netherlands. The most commonly resighted age group were adults, and most birds were sighted two years after ringing. Our analysis provides evidence for a change in the migration patterns of Lesser Black-backed Gulls, which may be explained by Baker’s exploratory migration model. It is probable that the gulls follow the rivers Tagus and Guadiana to the rubbish tips in the inner part of the Iberian Peninsula. The prevalence of adult birds could indicate that Lesser Black-backed Gull has become established as a regular wintering species in the inner part of the Iberian Peninsula. recoveries of ringed birds. He suggested that the principal factors influencing changes in migration patterns of Lesser Black-backed Gulls may have been climatic changes and the increased tendency of the birds to forage at human rubbish tips, although the increase in the population over the second half of the twentieth century (Barnes 1953