Abstract

The Caspian Gull Larus cachinnans has undergone a considerable range expansion in the last 100 years. This expansion is ongoing and, over recent decades, the species has established itself as a breeding bird in central and western Europe. The total central and western European population is estimated to number at least 7,600 pairs, including sizeable breeding populations in Poland, Belarus and Germany. It is likely that the population will continue to increase and expand. Through colonisation of new areas, Caspian Gull now comes into contact with other large white-headed gull species, notably Herring L. argentatus and Yellow-legged Gulls L. michahellis, which has led to hybridisation. The Caspian Gull offers an excellent opportunity to track the range extension of a species in real time.