The spectacled tern (''Onychoprion lunatus''), also known as the grey-backed tern, is a

seabird Seabirds (also known as marine birds) are birds that are adaptation, adapted to life within the marine ecosystem, marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Laridae.

Description

A close relative of the bridled and sooty terns (with which it is sometimes confused), the spectacled tern is less common than the other members of its

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

and it has been studied less. The three species, along with the Aleutian tern were recently split into a new genus ''Onychoprion'' from '' Sterna'' (Bridge ''et al.'', 2005). They resemble the sooty tern but with a grey back instead of a black one. Their breast and underparts are white, and they have a black eye line from the bill to the back of the head.

Distribution and habitat

The spectacled tern breeds on islands of the

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

. At the northern end of its distribution it nests in the Northwestern Hawaiian Islands (with the largest population being Lisianski Island) and two small islets off

Oahu Oahu (, , sometimes written Oahu) is the third-largest and most populated island of the Hawaiian Islands and of the U.S. state of Hawaii. The state capital, Honolulu, is on Oahu's southeast coast. The island of Oahu and the uninhabited Northwe ...

, in the east as far as the

Tuamotu Islands The Tuamotu Archipelago or the Tuamotu Islands (, officially ) are a French Polynesian chain of just under 80 islands and atolls in the southern Pacific Ocean. They constitute the largest chain of atolls in the world, extending (from northwest to ...

, with other

colonies A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their '' metropole'' (or "mother country"). This separated rule was often or ...

in the

Society Islands The Society Islands ( , officially ; ) are an archipelago in the South Pacific Ocean that includes the major islands of Tahiti, Mo'orea, Moorea, Raiatea, Bora Bora and Huahine. Politically, they are part of French Polynesia, an overseas country ...

, the

Line Islands The Line Islands, Teraina Islands or Equatorial Islands () are a chain of 11 atolls (with partly or fully enclosed lagoons, except Vostok and Jarvis) and coral islands (with a surrounding reef) in the central Pacific Ocean, south of the Hawa ...

Phoenix Islands The Phoenix Islands, or Rawaki, are a group of eight atolls and two submerged coral reefs that lie east of the Gilbert Islands and west of the Line Islands in the central Pacific Ocean, north of Samoa. They are part of the Kiribati, Republic ...

Mariana Islands The Mariana Islands ( ; ), also simply the Marianas, are a crescent-shaped archipelago comprising the summits of fifteen longitudinally oriented, mostly dormant volcanic mountains in the northwestern Pacific Ocean, between the 12th and 21st pa ...

and

American Samoa American Samoa is an Territories of the United States, unincorporated and unorganized territory of the United States located in the Polynesia region of the Pacific Ocean, South Pacific Ocean. Centered on , it is southeast of the island count ...

. There are unconfirmed reports of breeding as far south as

Fiji Fiji, officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consists of an archipelago of more than 330 islands—of which about ...

, and as far east as

Easter Island Easter Island (, ; , ) is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is renowned for its nearly 1,000 extant monumental statues, ...

. Little is known about the populations outside of Hawaii. Outside of the breeding season the species is partly migratory, with birds from the Hawaiian Islands flying south. It is thought that birds in other parts of the Pacific are also migratory, and will disperse as far as

Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...

, the Philippines, and

References

* Bridge, E. S.; Jones, A. W. & Baker, A. J. (2005): A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution. ''Molecular Phylogenetics and Evolution'' 35: 459–469
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* Mostello, C. S.; Palaia, N. A. & Clapp, B. (2000). Gray-backed Tern (''Sterna lunata''). ''In:'' Poole, A. & Gill, F. (eds.): ''The Birds of North America'' 525. The Birds of North America, Inc., Philadelphia, PA. {{Taxonbar, from=Q763931 Onychoprion Birds described in 1848 Taxa named by Titian Peale