The Sandwich tern is a medium-large tern with grey upperparts, white underparts, a yellow-tipped black bill, and a shaggy black crest which becomes less extensive in winter with a white crown. Young birds bear grey and brown scalloped plumage on their backs and wings. It is a vocal bird. It nests in a ground scrape and lays one to three eggs.
Like all Thalasseus terns, the Sandwich tern feeds by plunge diving for fish, usually in marine environments, and the offering of fish by the male to the female is part of the courtship display.
Taxonomy
Sandwich tern in flight
The terns are small to medium-sized seabirds, gull-like in appearance, but usually with a more delicate, lighter build and shorter, weaker legs. They have long, pointed wings, which gives them a fast buoyant flight, and often a deeply forked tail. Most species are grey above and white below, and have a black cap which is reduced or flecked with white in the winter.[3]
The Sandwich tern was originally described by ornithologist John Latham in 1787 as Sterna sandvicensis, but was moved to its current genus Thalasseus (Boie, 1822) following mitochondrialDNA studies which confirmed that the three types of head pattern (white crown, black cap, and black cap with a white blaze on the forehead) found among the terns corresponded to distinct clades.[2] The current genus name is derived from GreekThalassa, "sea", and sandvicensis, which, like the English name, refers to Sandwich, Kent, Latham's type locality.[4]
This bird has no subspecies. Two former subspecies are now treated as a separate species, Cabot's tern (T. acuflavidus); this breeds on the Atlantic coasts of North America, northern and eastern South America, and has wandered to Western Europe.
This is a medium-large tern, 36–41cm (14–16in) long with an 95–105cm (37–41in) wingspan, which is unlikely to be confused within most of its range. The weight ranges from 200-300 g.[5]
The Sandwich tern's thin, sharp bill is black with a yellow tip. Its short legs are black. Its upper wings are pale grey and its underparts white, and this tern looks very pale in flight, although the primary flight feathers darken during the summer.[6] In winter, the adult Sandwich tern's forehead becomes extensively white. Juvenile Sandwich terns have dark tips to their tails, an all-blackish bill (lacking the yellow tip, but sometimes yellowish at the base) and a scaly appearance on their back and wings, like juvenile roseate terns but with less black on the crown.[6]
A Sandwich tern (left, with a deformed bill) among lesser crested terns, Kerala, India
The lesser crested tern and elegant tern differ in having all-orange bills; lesser crested also differs in having a grey rump and marginally stouter bill, and elegant in having a slightly longer, more slender bill. The Chinese crested tern is more similar to the Sandwich tern, but has a reversal of the bill colour, yellow with a black tip; it does not overlap in range with the Sandwich tern so confusion is unlikely. Cabot's tern is the most similar, sharing the black bill with a yellow tip, but differs in the bill being obviously stouter, and also differs in moult timing, losing its black forehead earlier in the summer. Its juveniles also lack the scaly pattern of Sandwich tern, being a plainer grey (though this can be confused with first-winter plumage of Sandwich tern).[7]
The Sandwich tern is a vocal bird; its call is a characteristic loud grating kear-ik or kerr ink.[6]
Sandwich tern call
Behaviour
This species breeds in very dense colonies on coasts and islands, and exceptionally inland on suitable large freshwater lakes close to the coast. It nests in a ground scrape and lays one to three eggs. Unlike some of the smaller white terns, it is not very aggressive toward potential predators, relying on the sheer density of the nests—often only 20–30cm (7.9–11.8in) apart and nesting close to other more aggressive species such as Arctic terns and black-headed gulls to avoid predation.
Like all Thalasseus terns, the Sandwich tern feeds by plunge-diving for fish, almost invariably from the sea. It usually dives directly, and not from the "stepped-hover" favoured by Arctic terns. The offering of fish by the male to the female is part of the courtship display.
Plunge-diving Sandwich tern
Plunge-diving Sandwich tern
Sandwich tern looking for prey
Status
The Sandwich tern has an extensive global range estimated at 100,000–1,000,000km2 (39,000–386,000sqmi). It has a population estimated at 460,000–500,000 individuals. Population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as least concern.[1]
The Sandwich tern is among the taxa to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.[8] Parties to the agreement are required to engage in a wide range of conservation actions, which are describes in a detailed action plan. This plan should address key issues such as species and habitat conservation, management of human activities, research, education, and implementation.[9]
T. sandvicensis approaching its waiting offspring with a fish
Terns are seabirds in the family Laridae that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated as a subgroup of the family Laridae which includes gulls and skimmers and consists of eleven genera. They are slender, lightly built birds with long, forked tails, narrow wings, long bills, and relatively short legs. Most species are pale grey above and white below, with a contrasting black cap to the head, but the marsh terns, the Inca tern, and some noddies have dark plumage for at least part of the year. The sexes are identical in appearance, but young birds are readily distinguishable from adults. Terns have a non-breeding plumage, which usually involves a white forehead and much-reduced black cap.
The common tern is a seabird in the family Laridae. This bird has a circumpolar distribution, its four subspecies breeding in temperate and subarctic regions of Europe, Asia and North America. It is strongly migratory, wintering in coastal tropical and subtropical regions. Breeding adults have light grey upperparts, white to very light grey underparts, a black cap, orange-red legs, and a narrow pointed bill. Depending on the subspecies, the bill may be mostly red with a black tip or all black. There are several similar species, including the partly sympatric Arctic tern, which can be separated on plumage details, leg and bill colour, or vocalisations.
The roseate tern is a species of tern in the family Laridae. The genus name Sterna is derived from Old English "stearn", "tern", and the specific dougallii refers to Scottish physician and collector Dr Peter McDougall (1777–1814). "Roseate" refers to the bird's pink breast in breeding plumage.
The gull-billed tern, formerly Sterna nilotica, is a tern in the family Laridae. It is widely distributed and breeds in scattered localities in Europe, Asia, northwest Africa, and the Americas. The Australian gull-billed tern was previously considered a subspecies.
The lesser crested tern is a tern in the family Laridae.
The royal tern is a tern in the family Laridae. The species is endemic to the Americas, though vagrants have been identified in Europe.
The elegant tern is a tern in the family Laridae. It breeds on the Pacific coasts of the southern United States and Mexico and winters south to Peru, Ecuador and Chile.
The Chinese crested tern is a tern in the family Laridae. It is the county bird of Lienchiang County, Fuchien.
The greater crested tern, also called crested tern or swift tern, is a tern in the family Laridae that nests in dense colonies on coastlines and islands in the tropical and subtropical Old World. Its five subspecies breed in the area from South Africa around the Indian Ocean to the central Pacific and Australia, all populations dispersing widely from the breeding range after nesting. This large tern is closely related to the royal and lesser crested terns, but can be distinguished by its size and bill colour.
Thalasseus, the crested terns, is a genus of eight species of terns in the family Laridae.
Cabot's tern is a species of bird in subfamily Sterninae of the family Laridae, the gulls, terns, and skimmers. It is found in the eastern U.S. and Middle America, the Caribbean, Trinidad and Tobago, and in every mainland South American country except Bolivia and Paraguay.
The West African crested tern is a bird species in the family Laridae. Until 2020 it was considered a subspecies of the New World royal tern, Thalasseus maximus.
1 2 Bridge, Eli S.; Jones, Andrew W.; Baker, Allan J. (2005). "A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution". Molecular Phylogenetics and Evolution. 35 (2): 459–469. Bibcode:2005MolPE..35..459B. doi:10.1016/j.ympev.2004.12.010. PMID15804415.
↑ Snow, David; Perrins, Christopher M., eds. (1998). The Birds of the Western Palearctic (BWP) concise edition (2 volumes). Oxford: Oxford University Press. p.764. ISBN0-19-854099-X.
↑ Cramp, S. (1985). "Sterna sandvicensis Sandwich Tern". Handbook of the Birds of Europe, the Middle East and North Africa: the birds of the Western Palearctic. Volume 4: Terns to woodpeckers. Oxford: Oxford University Press. pp.48−62. ISBN978-0-19-857507-8.
Olsen, Klaus Malling; Larsson, Hans (1995). Terns of Europe and North America. London: Christopher Helm. ISBN0-7136-4056-1.
Stienen, Eric W.M. (2006). Living with gulls: trading of food and predation in the Sandwich Tern Sterna sandvicencis (PhD Thesis). University Groningen. hdl:11370/51438613-1ca3-4f4c-8cf1-5933785422a7.
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