Most terns are white, gray, and black; some species have
brightly colored bills and feet. They range in length from 20 to
51 cm (8 to 20 in), with short legs and long, narrow wings.
Most species have forked tails and straight, sharp bills. The
largest, the Caspian tern, is 51 cm (20 in) long and has a
wingspan of 135 cm (53 in). The smallest is the least tern,
which is 20 cm (8 in) long and has a wingspan of 51 cm (20
in). Most terns inhabit ocean coasts, where they feed on fish
and small marine invertebrates. Forster's tern of North
America nests in prairie marshes as well as on coasts.
Members of the genus known collectively as marsh terns are
confined to freshwater areas and feed primarily on insects.
Best known of these is the black tern of North America and
Most terns nest on the ground in dense colonies in open areas
such as beach or tundra; nests vary from a simple depression
to an elaborate structure of twigs, grass, and bits of shell.
The noddies, a genus of dark-colored tropical terns, nest in
trees or on cliff ledges. The white, or fairy, tern, which
inhabits tropical islands around the world, incubates its single
egg on a bare branch or in the crotch of a tree, with no nest.
Tropical terns rarely lay more than one egg, but northern
species such as the common tern and the roseate tern often
lay three and occasionally four eggs.
Terns are long-lived. Individuals continuing to breed at well
over 20 years of age have been documented in several
species. Most do not breed until they are three years old,
although they may return to their natal colonies earlier. The
sooty tern, which inhabits tropical islands, comes to land only
to breed, and its plumage is not waterproof. Young birds thus
spend as much as three years in the air (unless they can find
floating objects on which to sit) until they are of breeding
Scientific classification: Terns belong to the subfamily
Sterninae in the family Laridae, order Charadriiformes. The
arctic tern is classified as Sterna paradisaea, the Caspian tern
as Sterna caspia, the least tern as Sterna antillarum, and
Forster's tern as Sterna forsteri. Marsh terns make up the
genus Chlidonias. The black tern is classified as Chlidonias
niger. Noddies make up the genus Anous. The white, or fairy,
tern is classified as Cygis alba, the common tern as Sterna
hirundo, the roseate tern as Sterna dougallii, and the sooty
tern as Sterna fuscata.