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Sandwich Tern | Thalasseus sandvicensis
Grote stern | Charrán patinegro
The Sandwich Tern is a slender crested tern with a thin black bill with a yellow tip. American birds belong to the form acuflavidus, which some taxonomists treat as a separate species. In the guide area it breeds locally along the Gulf of Mexico and outside the breeding season occurs along both coasts south to Panama, often together with Royal Terns.
Voice
A loud, rasping kirr-ick or kerrrick, higher and harsher than the call of Royal Tern; often given in flight.
Recording: Paul Kelly — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
37–43 cm, slender, with long, narrow wings, a short forked tail and a long, thin bill. The bill is black with a yellow tip; the yellow-billed Cayenne form eurygnatha of the southern Caribbean and South America, and intermediates with a blotched bill, are rare in the guide area. In breeding plumage a black cap with a shaggy crest on the hindcrown; early in the season and in winter the forehead is white and only a black-speckled hindcrown remains. The upperparts are very pale grey, the underparts white. The legs are black. Juveniles have dark V-shaped marks on the back and wings and a shorter, all-dark bill.
Confusion species
Royal Tern Thalasseus maximus is clearly larger, with a thick orange bill. Elegant Tern Thalasseus elegans has a long, slightly drooping orange-yellow bill and a longer crest. Gull-billed Tern Gelochelidon nilotica has a short, thick, all-black bill, longer legs and no crest. Forster's Tern Sterna forsteri is smaller, with orange legs and, in non-breeding plumage, a black eye patch instead of a black hindcrown.
Habitat
Coastal waters, shallow bays, lagoons, estuaries and harbours; rarely far out at sea or inland. It fishes by plunge-diving from a searching flight. It roosts in flocks on beaches, sandbars, quays and jetties. It breeds in dense colonies on bare islets and sandbars, often together with Royal Terns.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
Breeds locally on islets along the Gulf of Mexico, including off the coast of the Yucatán Peninsula. Outside the breeding season along the entire Caribbean and Atlantic coast from Mexico to Panama, and in smaller numbers also along the Pacific coast. Outside the guide area the species breeds along the Atlantic and Gulf coasts of the United States, in the Caribbean and along the coast of South America; the nominate form breeds in Europe.
- Resident
- Summer visitor (c. Apr–Sep)
- Winter visitor (c. Oct–Mar)
- Passage (Mar–Apr, Oct–Nov)
- dark = core range, pale = thinly spread
How and when to look
Resting flocks of terns on beaches, jetties and sandbars along the Caribbean coast, such as in Yucatán and Belize, are the place to find Sandwich Terns among Royal Terns. At close range the thin black bill with a yellow tip is the decisive feature; the rasping call gives the species away in flight too.
Conservation status
Not threatened. The species is numerous, but breeds in a limited number of large colonies on low islets, which are vulnerable to disturbance, egg collecting, introduced predators and flooding during storms.
Scientific name
Thalasseus sandvicensis | (Latham, 1787)
Latham described the species in 1787 as Sterna sandvicensis; because it was later moved to another genus, the author and year stand in brackets. The genus Thalasseus was introduced in 1822 by Boie. Thalasseus derives from Ancient Greek thalassa 'sea'. sandvicensis means 'of Sandwich', the town in the English county of Kent that was the type locality. The specimen the first description was based on came from Sandwich, Kent, England.