The Caspian Tern (Hydroprogne caspia, formerly Hydroprogne tschegrava) is a species of bird with an extensive range, but scattered distribution. It is found in North America, Europe, Asia, Africa, Australia, and New Zealand. In North America it is found on large lakes and ocean coasts. In Europe it is found mainly around the Baltic Sea and the Black Sea. North American birds migrate to southern coasts, the West Indies and northern South America. European and Asian birds migrate to the Old World tropics. African and Australian birds are mostly resident and only move short distances. The global population is about 50,000 pairs. Most populations are stable, but the Baltic Sea population is declining.
This bird is the largest species of tern at 18.9 to 22 inches long. It has a wingspan of 50 to 55 inches and weighs 20.25 to 27.5 ounces. The adult has black legs, and a long thick red-orange bill with a black tip. The upperwings and back are pale gray, and the underwings are pale with dark primary feathers. In flight, the wing tips are black on the underside. It has a black cap that is present throughout the year (unlike most other terns), but there is some white streaking on the forehead. The call is a loud heron-like croak.
The diet of the Caspian Tern consists of mostly fish, which it dives for. It hovers high over the water and then plunges without warning. Insects and the young and eggs of other birds are also sometimes taken. This bird may fly up to 37.5 miles from its breeding colony to catch fish. It will either fish on freshwater lakes or at sea.
Breeding takes place in the spring and summer. These birds nest together in colonies, or singly in a mixed colony of other terns and gulls. The nest is on the ground among gravel or sand, or sometimes on vegetation. The female lays one to three pale blue-green eggs with heavy brown spotting. Incubation lasts for 26 to 28 days. The newborn chicks are pale cream to darker gray-brown in color. This coloration helps the adults recognize their own young when returning to the colony from feeding trips. The chicks fledge after 35 to 45 days.
The Caspian Tern is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.