The Common Tern (Sterna hirundo) is a seabird of the tern family Sternidae. This bird has a circumpolar distribution breeding in temperate and sub-arctic regions of Europe, Asia and east and central North America. It is strongly migratory, wintering in the subtropical and tropical oceans.
This species breeds in colonies on coasts and islands and often inland on suitable waters. This latter practice is assisted by the provision of floating "tern rafts" to give a safe breeding area. It lays two to four eggs. Like all white terns, it is fiercely defensive of its nest and young and will attack humans and other large predators, usually attacking the back of the head. It is too small to cause serious injury, and rarely draws blood, a distinction from the sharper-billed Arctic Tern.
Like all Sterna terns, Common Tern feeds by plunge-diving for fish, usually from saline environments. It usually dives directly, and not from the "stepped-hover" favoured by Arctic Tern. The offering of fish by the male to the female is part of the courtship display.
This is a medium-sized tern, most readily confused within its range with the similar Arctic Tern Sterna pardisaea and Roseate Tern Sterna dougalli .
Its thin sharp bill is red with a dark tip. Its longish legs are also red. Its upperwings show a dark primary wedge, unlike Arctic, in which they are uniformly grey. Its long tail extends only to the wingtips on the standing bird, unlike Arctic and Roseate Terns, which extend past the wingtips. It is not as pale as Roseate Tern, and has longer wings.
In winter, the forehead and underparts are white. Juvenile Common Terns show extensive ginger coloration and lack the scaly appearance of juvenile Roseate Terns.
The call is a clear piping, like Arctic Tern.