Arctic Tern
: Animalia  : Chordata  : Aves  : Charadriiformes  : Sternidae  : Sterna  : paradisaea
Binomial name
Sterna paradisaea Pontopiddan, 1763

The Arctic Tern (Sterna paradisaea) is a seabird of the tern family Sternidae. This bird has a circumpolar distribution breeding abundantly in arctic and sub-arctic regions of Europe, Asia and North America as far south as Brittany and Massachusetts.

This species is strongly migratory, wintering in the Antarctic. This 19,000 km (12,000 mile) journey ensures that this bird sees more daylight than any other creature on the planet. One particularly spectacular example involved an Arctic Tern ringed as a chick not yet able to fly, on the Farne Islands off the Northumberland coast in eastern Britain in summer 1982, which reached Melbourne, Australia in October 1982, a sea journey of over 22,000 km (14,000 miles) in just three months from fledging.

The Arctic Tern breeds in colonies on coasts, islands and occasionally inland on tundra near water. It lays up to four eggs. It is the most aggressive tern, fiercely defensive of its nest and young, and will attack humans and other large predators, usually striking the top or back of the head. Although it is too small to cause serious injury, it is capable of drawing blood. In this it differs from the Common Tern, which usually veers off at the last moment, relying on bluff to deter predators without actually striking.

Like all Sterna terns, Arctic Tern feeds by plunge-diving for fish, usually from the sea, though occasionally also fishing in coastal freshwater lagoons. It often dives from a "stepped-hover". The offering of fish by the male to the female is part of the courtship display.

This is a medium-sized tern, 33-39cm long with a 66-77cm wingspan. It is most readily confused within its range with the similar Common Tern Sterna hirundo and Roseate Tern Sterna dougalli. Unlike these two, its thin sharp bill is entirely dark red, as are its short legs. Its upperwings are uniformly grey. Its long tail extends beyond the wingtips on the standing bird, unlike Common Tern, but is shorter than that of Roseate Tern. It is not as pale as Roseate Tern, and has longer wings.

On the wintering grounds, Arctic Tern also has to be distinguished from the Antarctic Tern Sterna vittata and Kerguelen Tern Sterna virgata; the six-month difference in moult is the best clue here, with Arctic Terns being in winter plumage during the southern summer.

In winter, the forehead and underparts are white. Juvenile Arctic Terns lack the extensive ginger coloration of young Common Terns and the scaly appearance of juvenile Roseate Terns.

The call is a clear piping, similar to that of the Common Tern, but higher pitched and more strident.