Sandwich Tern
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Sterna sandvicensis Latham, 1787 |
The Sandwich Tern (Thalasseus sandvicensis, syn. Sterna sandvicensis - see Bridge et al, 2005) is a seabird of the tern family Sternidae. It is very closely related to the Lesser Crested Tern T. bengalensis, Chinese Crested Tern T. bernsteini, and Elegant Tern T. elegans, and has been known to interbreed with Lesser Crested.
This bird has three subspecies:
- T. s. sandvicensis breeds on the Atlantic and Mediterranean coasts of Europe, and winters off western Africa and Arabia.
- The marginally smaller T. s. acuflavida breeds on Atlantic coasts of North America, wintering in the Caribbean and further south, and has wandered to western Europe.
- Yellow-billed T. s. eurygnatha (sometimes treated as a separate species, Cayenne Tern T. eurygnatha) breeds on the Atlantic coast of South America from Argentina north to the Caribbean, intergrading with T. s. acuflavida in the north of its range.
In birds, the specific name sandvicensis usually denotes that the species was first described from Hawai‘i, formerly known as "Sandwich Islands". The Sandwich Tern does not occur there; in this case, its specific name refers to Sandwich, Kent, Latham's type locality.
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 apart) and nesting close to other more aggressive species such as Arctic Terns and Black-headed Gulls to avoid predation.
Like all Thalasseus terns, 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 Tern. The offering of fish by the male to the female is part of the courtship display.
This is a medium-large tern, 37-43cm long with an 85-97cm wingspan, which is unlikely to be confused within most of its range, although the South American race could be confused with the Elegant Tern.
The Sandwich Tern's thin sharp bill is black with a yellow tip, except in the yellow or orange billed South American race. Its short legs are black. Its upperwings are pale grey and its underparts white, and this tern looks very pale in flight, although the primary flight feathers darken during the summer. The call is a characteristic loud grating noise.
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, slenderer bill. Chinese Crested Tern is the most similar to Sandwich, but has a reversal of the bill colour, yellow with a black tip; it does not overlap in range with Sandwich Tern so confusion is unlikely.
In winter, the Sandwich Tern's forehead becomes white. Juvenile Sandwich Terns have a scaly appearance like juvenile Roseate Terns.
The Sandwich Tern is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.
[edit] References
- BirdLife International (2004). Sterna sandvicensis. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Database entry includes justification for why this species is of least concern
- 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. PDF fulltext
- Harrison, Peter (1988): Seabirds (2nd edition). Christopher Helm, London ISBN 0-7470-1410-8
- National Geographic Society (2002): Field Guide to the Birds of North America. National Geographic, Washington DC. ISBN 0-7922-6877-6
- Olsen, Klaus Malling & Larsson, Hans (1995): Terns of Europe and North America. Christopher Helm, London. ISBN 0-7136-4056-1
[edit] External links
- Sandwich Tern videos on the Internet Bird Collection
