Terns are seabirds in the family Sternidae, previously considered a subfamily (Sterninae) of the gull family Laridae
. They form a lineage with the gulls and skimmers which in turn is related to skuas and auks. Terns have a worldwide distribution.

Most terns were formerly treated as belonging to one large genus Sterna, with the other genera being small.
However analysis of DNA sequences supports the splitting of Sterna into several smaller genera (see list, below)

Many terns breeding in temperate zones are long-distance migrants, and the Arctic Tern probably sees more daylight than any
other creature, as it migrates from its northern breeding grounds to Antarctic waters.

They are, in general, medium to large birds, typically with grey or white plumage, often with black markings on the head.
They have longish bills and webbed feet. They are lighter bodied and more streamlined than gulls, and look elegant in flight
with long tails and long narrow wings. Terns in the genus Sterna have deeply forked tails, those in Chlidonias and Larosterna
shallowly forked tails, while the noddies (genera Anous, Procelsterna, Gygis) have unusual 'notched wedge' shaped tails,
the longest tail feathers being the middle-outer, not the central nor the outermost.

Terns ranges in size from the Least Tern, at 42 g (1.5 oz) and 23 cm (9 inches), to the Caspian Tern, at 630 g (1.4 lbs)
and 53 cm (21 inches). They make harsh, single-note calls.

Engelsk	Norsk	Latinsk
Pied Kingfisher	Terneisfugl	Ceryle rudis
Whiskered Tern	Hvitkinnsvartterne	Chlidonias hybrida
White-winged Tern	Hvitvingesvartterne	Chlidonias leucopterus
Black Tern	Svartterne	Chlidonias niger
Gull-billed Tern	Sandterne	Gelochelidon nilotica
White Tern	Silketerne	Gygis alba
Caspian Tern	Rovterne	Hydroprogne caspia
Inca Tern	Inkaterne	Larosterna inca
Aleutian Tern	Beringterne	Onychoprion aleuticus
Bridled Tern	Tøyleterne	Onychoprion anaethetus
Sooty Tern	Sotterne	Onychoprion fuscatus
Gray-backed Tern	Polynesiaterne	Onychoprion lunatus
Large-billed Tern	Tykknebbterne	Phaetusa simplex
Black-bellied Tern	Svartbukterne	Sterna acuticauda
Black-fronted Tern	Maoriterne	Sterna albostriatus Chlidonias albostriatus
River Tern	Flodterne	Sterna aurantia
Roseate Tern	Rosenterne	Sterna dougallii
Forster's Tern	Prærieterne	Sterna forsteri
South American Tern	Svaleterne	Sterna hirundinacea
Common Tern	Makrellterne	Sterna hirundo
Arctic Tern	Rødnebbterne	Sterna paradisaea
White-cheeked Tern	Hvitkinnterne	Sterna repressa
White-fronted Tern	Nyzealandterne	Sterna striata
Black-naped Tern	Svartnakketerne	Sterna sumatrana
Snowy-crowned Tern	Svartøreterne	Sterna trudeaui
Kerguelen Tern	Kerguelenterne	Sterna virgata
Antarctic Tern	Sørhavsterne	Sterna vittata
Little Tern	Dvergterne	Sternula albifrons
Least Tern	Amerikadvergterne	Sternula antillarum
Damara Tern	Benguelaterne	Sternula balaenarum
Peruvian Tern	Perudvergterne	Sternula lorata
Fairy Tern	Alveterne	Sternula nereis
Saunders' Tern	Araberdvergterne	Sternula saundersi
Yellow-billed Tern	Amazondvergterne	Sternula superciliaris
Lesser Crested Tern	Bengalterne	Thalasseus bengalensis
Great Crested Tern	Hinduterne	Thalasseus bergii
Chinese Crested Tern	Kinaterne	Thalasseus bernsteini
Elegant Tern	Langnebbterne	Thalasseus elegans
Royal Tern	Kongeterne	Thalasseus maximus
Sandwich Tern	Splitterne	Thalasseus sandvicensis

Aleuta-tern: Sterna aleutica - sterna kamtschatica

Sterna
Sterna is a genus of terns in the bird family Sternidae. It used to encompass most "white" terns indiscriminately,
but mtDNA sequence comparisons have recently determined that this arrangement is paraphyletic.
It is now restricted to the typical large white terns occurring near-globally in coastal regions.
Of those, 14 are listed below, under Latin as Sterna....

One Arctic Tern, ringed as a chick (not yet able to fly) on the Farne Islands off the Northumberland coast in eastern
Great Britain in summer 1982, reached Melbourne, Australia in October 1982, a sea journey of over 22,000 km
(14,000 statute miles) in just three months from fledging—an average of over 240 km per day, and one of the longest
journeys ever recorded for a bird.

Chlidonias
The name marsh tern refers to terns of the genus Chlidonias, which are typically found in freshwater marshes,
rather than coastal locations. There are four species.

Onychoprion
Onychoprion, the "brown-backed terns", is a genus of seabirds in the tern family. Although the genus was first described
in 1832 by Johann Georg Wagler the four species in the genus were until recently retained in the larger genus Sterna,
the genus that most terns are in .

Three of the four species are tropical, and one has a sub-polar breeding range. The Sooty Tern has a pan-tropical distribution;
the Bridled Tern also breeds across the Tropical Atlantic and Indian Ocean but in the central Pacific it is replaced by the
Spectacled Tern. The Aleutian Tern breeds around Alaska and Siberia but winters in the tropics around South East Asia.

Thalasseus
Thalasseus, the crested terns, is a genus of six species of seabirds in the tern family. Thalasseus signifies a "creature of the sea".
It has a worldwide distribution, and many of its species are abundant and well-known birds in their ranges.

These large terns breed in very dense colonies on coasts and islands, and exceptionally inland on suitable large freshwater lakes close to the coast. They nest in a ground scrape.

Thalasseus terns feed by plunge-diving for fish, almost invariably from the sea. They usually dive directly, and not from the
"stepped-hover" favoured by, for example, the Arctic Tern. The offering of fish by the male to the female is part of the courtship.

These species have long thin sharp bills, usually a shade of yellow or orange except in the Sandwich Tern where the bill is black
with a yellow tip in most subspecies. All species have a shaggy crest. In winter, the Thalasseus terns' foreheads become white.