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Length 36â€“46 cm (14Â¼-18 in), wingspan 85-97 cm, weight 130-285 g
Slender black bill with pale yellow tip
Feet have yellow soles
Light grey above with blackish wing tips. The rump and rather short forked tail are white. Underparts white (rarely faintly tinged creamy-pink).
Summer Adult: forehead, crown and nape black. Loose long feathers at the nape form a crest in the wind or when excited. Winter Adult black areas on the front and top of the head turn white and speckled black on the crest. This can happen as early as June, more usually from July onward. Juvenile: scalloped with blackish-brown chevrons on mantle and wings, brown on forehead, crown and nape; white elsewhere. Bill is blackish-yellow to all black. First-winter: mantle becomes pale grey, and forehead white after post-juvenile moult in a month or two after fledging; some scalloping remains on wing coverts.
Gull-billed Tern is superficially similar in plumage, but differs structurally, with longer legs, shorter broader wings (more gull-like in flight), shorter, thicker, all-black bill, no crest, and a pale grey rump. Lesser Crested and Elegant Terns are structurally very similar, but differ in their bright orange bills, and in Lesser Crested, also a pale grey rump, and in Elegant, a longer bill. Juvenile Roseate Tern has a similar scalloped mantle pattern, but is smaller, has a darker forehead, and a longer tail.
Sandwich Tern, fresh juvenile (bill not yet fully grown) Photo by Xmor Farne Islands, Northumberland, UK, July 2014
A breeding summer visitor widely on the coasts of Europe and southwestern Asia (Estonia west to Ireland, and western France, and east through the Mediterranean from northeast Spain to the Black Sea and Caspian Sea), wintering on the west and north coasts of Africa, the Arabian Sea, and locally of western India. A separate [sub]species (see Taxonomy, below) breeds on the Atlantic coasts of North and South America, wintering additionally on the Pacific coast of northern South America.
T. s. sandvicensis breeds on the Atlantic and Mediterranean coasts of Europe and winters on the west coast of Africa.
Cabot's Tern, adult summer Photo by bobsofpa South Padre Island, Texas, April 2016; note stout-based bill compared to Sandwich Tern
Cabot's TernThalasseus (sandvicensis) acuflavidus
T. s. acuflavidus breeds on Atlantic coasts of North America and winters on Caribbean and northern South American coasts.
T. s. eurygnathus breeds and winters on the Atlantic coast of South America.
A study of genetic data showed that acuflavidus (including eurygnathus) was more closely related to Elegant Tern than to Sandwich Tern, and should be treated as separate species, Thalasseus acuflavidus. It differs from sandvicensis most obviously in a shorter, stouter bill, with in South American eurygnathus populations an increasing amount of yellow in the bill. There are also differences in timings of wing moult, and in the juvenile plumage having less scaling on the mantle. In the past, the populations with all or mostly yellow bills were sometimes treated as a separate species, Cayenne Tern T. eurygnathus, but in genetics these are very close to Cabot's Tern.
There are one or two records of transatlantic vagrants of each of T. s. sandvicensis in North America and T. s. acuflavidus in Europe; in both cases including ringed birds which allowed confirmed identification at a time when field identification between them was still poorly researched.
Sangster, G., et al. (2011). Taxonomic recommendations for British birds: seventh report. Ibis 153: 883â€“892.
Efe, M. A., Tavares, E. S., Baker, A. J. & Bonatto, S. L. (2009). Multigene phylogeny and DNA barcoding indicate that the Sandwich tern complex (Thalasseus sandvicensis, Laridae, Sternini) comprises two species. Mol. Phyl. Evol. 52: 263â€‘267.
Garner, M., Lewington, I., & Crook., J. (2007). ldentification of American Sandwich Tern. Dutch Birding 29: 273-287.