Terns are the slender, elegant cousins of the gulls, with narrow pointed wings, forked tails that earned them the name sea swallows, and sharp bills. There are about 40 species, from the least tern at 9 inches (23 cm) to the Caspian tern at 21 inches (53 cm). The Sandwich tern pictured is 14-17 inches (36-43 cm) long with a wingspan of 3-3.3 feet (0.9-1 m), a shaggy black crest and a black bill with a yellow tip.
Most terns are white and grey with a black cap in the breeding season, which shrinks to a patch behind the eye in winter. They are light birds, weighing only 7-10 oz (200-280 g) in the case of the Sandwich tern.
Terns breed on coasts and inland waters all over the world, nesting in colonies on beaches, sandbars, islands and marshes, and sometimes on flat rooftops. The Arctic tern breeds around the Arctic and winters at the edge of the Antarctic pack ice, so it sees more daylight than any other animal.
Terns eat small fish and crustaceans. They hunt by flying slowly over the water with the bill pointed down, hovering when they spot prey, then plunging head first to snatch it from just below the surface. Unlike gannets they barely go under.
The Arctic tern makes the longest migration of any animal, a round trip of up to 44,000 miles (70,000 km) each year between the two poles. Over a 30-year life that is the distance to the Moon and back three times.
Courting males present fish to females, and pairs nest in dense colonies that mob any predator, diving at foxes, gulls and people and striking them on the head.
Terns form the subfamily Sterninae within the family Laridae, alongside gulls and skimmers. The IUCN lists the Sandwich tern and most other species as Least Concern. The Chinese crested tern, with fewer than 100 birds, is Critically Endangered, and several beach-nesting species such as the least tern and roseate tern are protected locally.
Disturbance of nesting beaches, flooding from storms and rising seas, and avian flu, which hit Sandwich tern colonies hard in 2022, are the main threats.
