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Caspian Gulls are large, white-headed gulls. They take four years to reach maturity, so there are five different phases of plumage. During the breeding season, adult Caspian Gulls have an all-white head and front. The belly can have a light-grey tinge. The wings are grey, with black tips on the outer primaries, which in turn have white spots on them. In-flight the wings show white leading and trailing edges. The tail is white. Outside the breeding season the back of the head can be slightly streaked grey, but otherwise, except for wear and tear, the plumage remains the same. Their most prominent (but not unique!) feature is the rather long, slender yellow bill with a red spot near the tip of the lower mandible. The irises are pale-grey. The colour of the legs and feet can vary, from fleshy pale-pink via grey to yellow. There are 4 different immature plumages. The plumage of third-year birds already closely resembles that of adults, but with some residual grey streaking on the head, nape of the neck and some of the flight feathers. The bill is mostly dark-yellow, with a black spot (across both mandibles) near the tip. The legs and feet are pale-pink. Second-year birds have an almost all-white head, a mostly light-grey front and mottled grey sides. The wings are mostly grey, with some mottling on the coverts; the tips of the outer primaries and the tail are black. The legs and feet are pale-pink. The irises are quite dark. The frontal half of the bill is partly black, while the rest is dark-yellow. Except for their almost all-white head and chest and a grey belly, first-year Caspian Gulls are mottled grey all over, with some streaking on the sides, but a bolder scalloped pattern on the wings. The irises are dark. The bill is black with a greyish base. Juveniles have an all-black bill, a strongly streaked neck, a finely scalloped front and boldly scalloped brownish-grey wings.

The overall distribution of this species can be assessed, and specific locations where birds have been spotted can be found, based on individual sighting reports submitted by birdwatchers to ebird.org .

The global distribution of the Caspian Gull is available HERE .

Caspian Gulls are a partly migratory species. Most of the population breeds around the Black Sea and the Caspian Sea and further eastwards into Central Asia, to north-western China. In recent decades they have been extending their range north-westwards into eastern Europe, breeding in Poland and eastern Germany. Some birds migrate South during the winter, to the Red Sea and the Persian Gulf, while others disperse into Western Europe, mostly around the Baltic Sea, but also towards the coastline of the North Sea.

In Europe Caspian Gulls are partly resident, partly winter visitors. They breed in wetlands mostly in Poland, along the lower Danube river, along the North coast of the Black Sea, along the Dnjepr river, along the lower Volga river and along the North coast of the Caspian Sea. There is also an overwintering population at the northern tip of the Adriatic Sea, around Venice, Italy. On both sides of the Volga, and from there eastwards, they are summer breeding migrants.

Outside the breeding season Caspian Gulls are mostly coastal species.

G. Pinelas reports finding Caspian Gulls at the Port of Sesimbra, Setubal, Portugal, in February 2018.

J. Pires spotted a Caspian Gull on a pelagic off Sagres, Algarve, Portugal, in November 2022.