Caspian Gull is a name applied to the gull taxon Larus (argentatus) cachinnans, a member of the Herring Gull/Lesser Black-backed Gull complex.
It is a large gull at 59-67 cm (23-26 in) and a body mass of 680-1,500 g (1.5-3.3 lb). with a long, slender bill, ccentuated by the sloping forehead. The legs, wings and neck are longer than those of the Herring Gull and Yellow-legged Gull. The eye is small and often dark, the legs vary from pale pink to a pale yellowish colour. The back and wings are a slightly darker shade of grey than the Herring Gull but slightly paler than the Yellow-legged Gull. The outermost primary feather has a large white tip and a white tongue running up the inner web.
First-winter birds have a pale head with dark streaking on the back of the neck. The underparts are pale and the back is greyish. The greater and median wing-coverts have whitish tips forming two pale lines across the wing.
The Caspian Gull breeds around the Black and Caspian Seas, extending eastwards across Central Asia to north-west China. In Europe it has been spreading north and west and now breeds in Poland and eastern Germany. Some birds migrate south as far as the Red Sea and Persian Gulf while others disperse into Western Europe, in countries such as Sweden, Norway and Denmark. Small numbers are now seen regularly in Britain, especially in South-east England, East Anglia and the Midlands.