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 adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same enviro ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Laridae Laridae is a family of seabirds in the order Charadriiformes that includes the gulls, terns, skimmers and kittiwakes. It includes around 100 species arranged into 22 genera. They are an adaptable group of mostly aerial birds found worldwide. T ...

Description

A close relative of the bridled and

sooty tern The sooty tern (''Onychoprion fuscatus'') is a seabird in the family Laridae. It is a bird of the tropical oceans, returning to land only to breed on islands throughout the equatorial zone. Taxonomy The sooty tern was described by Carl Linnaeu ...

s (with which it is sometimes confused), the spectacled tern is less common than the other members of its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

and it has been studied less. The three species, along with the

Aleutian tern The Aleutian tern (''Onychoprion aleuticus'') is a migratory bird living in the subarctic region of the globe most of the year. It is frequently associated with the Arctic tern, which it closely resembles. While both species have a black cap, th ...

were recently split into a new genus ''Onychoprion'' from ''

Sterna ''Sterna'' is a genus of terns in the bird family Laridae. The genus used to encompass most "white" terns indiscriminately, but mtDNA sequence comparisons have recently determined that this arrangement is paraphyletic. It is now restricted to t ...

'' (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. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

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

. At the northern end of its distribution it nests in the

Northwestern Hawaiian Islands The Northwestern Hawaiian Islands or Leeward Hawaiian Islands are a series of islands and atolls in the Hawaiian island chain located northwest (in some cases, far to the northwest) of the islands of Kauai and Niihau. Politically, they are all p ...

(with the largest population being

Lisianski Island Lisianski Island ( Hawaiian: ''Papa‘āpoho'') is one of the Northwestern Hawaiian Islands, with a land area of and a maximum elevation of above sea level. It is a low, flat sand and coral island about northwest of Honolulu, Hawaii. The isla ...

) and two small islets off

Oahu Oahu () (Hawaiian language, Hawaiian: ''Oʻahu'' ()), also known as "The Gathering place#Island of Oʻahu as The Gathering Place, Gathering Place", is the third-largest of the Hawaiian Islands. It is home to roughly one million people—over t ...

, in the east as far as the

Tuamotu Islands The Tuamotu Archipelago or the Tuamotu Islands (french: Îles Tuamotu, 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, extendin ...

, with other

colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...

in the

Society Islands The Society Islands (french: Îles de la Société, officially ''Archipel de la Société;'' ty, Tōtaiete mā) are an archipelago located in the South Pacific Ocean. Politically, they are part of French Polynesia, an overseas country of the F ...

, the

Line Islands The Line Islands, Teraina Islands or Equatorial Islands (in Gilbertese, ''Aono Raina'') are a chain of 11 atolls (with partly or fully enclosed lagoons) 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 the Marianas; in Chamorro: ''Manislan Mariånas'') are a crescent-shaped archipelago comprising the summits of fifteen longitudinally oriented, mostly dormant volcanic mountains in the northwestern Pacific Ocean, betw ...

and

American Samoa American Samoa ( sm, Amerika Sāmoa, ; also ' or ') is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the island country of Samoa. Its location is centered on . It is east of the International ...

. There are unconfirmed reports of breeding as far south as

Fiji Fiji ( , ,; fj, Viti, ; Fiji Hindi: फ़िजी, ''Fijī''), 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 ...

, and as far east as

Easter Island Easter Island ( rap, Rapa Nui; es, Isla de Pascua) 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 most famous for its nearl ...

. 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 (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...

, 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