About Hydroprogne caspia (Pallas, 1770)
This species, the Caspian tern, is the world's largest tern. It measures 48–60 cm (19–24 in) in length, has a wingspan of 127–145 cm (50–57 in), and weighs 530–782 g (18.7–27.6 oz). Adult individuals have black legs, and a long, thick red-orange bill with a small black tip. They have a white head with a black cap, and white neck, belly, and tail. The upper wings and back are pale grey, while the underwings are pale with dark primary feathers. When in flight, the tail is less forked than that of other terns, and the underside of the wingtips is black. In winter, the black cap remains present (unlike in many other tern species), but gains some white streaking on the forehead. Its call is a loud heron-like croak. The breeding habitat of this species is large lakes and ocean coasts in North America (including the Great Lakes), with local breeding populations in Europe (mainly around the Baltic Sea and Black Sea), Asia, Africa, and Australasia (Australia and New Zealand). Birds that breed in North America migrate to southern coasts, the West Indies, and the northernmost part of South America. Birds that breed in Europe and Asia spend the non-breeding season in the Old World tropics. Birds from Africa and Australasia are either resident or only disperse over short distances. In 2016, a pair of Caspian terns bred successfully in Cape Krusenstern National Monument in northwestern Alaska. This site is 600 km further north than any previous North American breeding record for the species. This event was part of a general trend of species moving north in Alaska, a tendency attributed to global warming. The global population of Caspian terns is about 50,000 pairs. Population numbers are stable in most regions, but the Baltic Sea population (counted at 1400–1475 pairs in the early 1990s) is declining and is a focus of conservation concern. The Caspian tern is one of the species covered by the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA).
