Sandwich tern

Voice

A loud, hard, grating disyllabic kirrick or kerr-ick that carries for kilometres and defines the sound of a Wadden colony. Young birds beg with a thin, insistent, plaintive psieuw, heard along the beach from July to September as they chase their parents. In the colony a continuous shrill roar rises from April to June, swelling in waves whenever a block of birds lifts off together.

Identification

Large, white and long-winged, with stiff deep wingbeats and steep plunge-dives from as much as fifteen metres. The bill is long, slender and black with a sharply demarcated yellow tip, as though dipped in wax; the legs are black. At rest the black cap runs back into a shaggy, raisable crest, giving the characteristic spiky rear head. The mantle is very pale pearl grey, light enough that the bird reads as white at distance; only the outer primaries darken through the summer with wear, forming a grey wedge. From June onwards the forehead turns white, so in July and August almost every bird shows a white face and a black rear crown. Juveniles have scaly black-and-buff upperparts, a shorter bill without the yellow tip, and beg loudly in their parents' wake. AviList 2025 places the American birds, long carried on checklists as Thalasseus acuflavidus, within this species, while several other lists keep them apart. Taken as forms of one species, they part company on three points. European sandvicensis has a long, slender bill whose yellow runs well back and blends into the black. American birds, from the south-eastern United States south into South America, average a shorter and deeper bill with a straighter gonys and a shorter, more sharply cut-off yellow tip, often little more than the nail. Their mantle is a shade darker pearl grey, and the outer primaries carry more dark, forming a more solid blackish wedge in fresh feathers with shorter silvery tongues on the inner webs.

Confusion species

Common and Arctic Terns are smaller and more compact, with a red bill and grey underparts, and they fly more loosely and lightly; Sandwich Tern looks whiter and far stiffer-winged. Gull-billed Tern is the real trap in southern Europe: a short, thick, wholly black bill without a yellow tip, longer black legs, broader wings and a gull-like flight, and it hunts insects and lizards over land instead of diving at sea. At distance in the Delta the voice helps: the disyllabic kirrick of Sandwich Tern is sharp and grating, while Gull-billed gives a nasal, laughing ge-gerrek. Far out at sea a Sandwich Tern can suggest a Little Gull or Kittiwake, but the black bill with the yellow tip and the plunge-dive settle it. Picking out an American bird within the species is another exercise altogether. The characters of the two forms overlap across their whole range and none carries a record on its own: bill shape, mantle tone and primary pattern have to agree together, and the mantle only with a European bird alongside in the same light. In practice a European claim does not close without a series of sharp photographs of bill, mantle and spread wing, and in several cases DNA from a moulted feather or a faecal sample before a committee will move. Allow as well for the South American form eurygnathus, Cayenne Tern, which sits between the two and carries a largely yellow to orange-yellow bill. Age the bird too: a first-summer European tern with a worn outer hand and a stubby bill imitates most of these characters at once.

Habitat

Strictly coastal: it breeds in dense colonies on bare islands and shell banks, almost always inside or beside a Black-headed or Mediterranean Gull colony, which defends the ground against predators. It feeds well offshore and in tidal gullies, plunge-diving for sandeel, herring and sprat, and rests in packs on beaches, groynes and sand flats. Outside the breeding season it migrates along the coastline and lingers in shallow bays, lagoons and salt pans.

Range and movements

From the Baltic and the British Isles to the Black Sea and the Caspian region, with the main North Sea colonies in the Netherlands and Germany. The Netherlands holds a large share of the north-west European population, with colonies on Griend, Texel and in the Delta; birds from there winter as far as Ghana and Mauritania. In Spain it breeds in small numbers in the Ebro delta and in Andalusian salt pans, and is a common passage migrant and winter visitor along almost the whole coast. American birds breed along the south-eastern United States, the Gulf of Mexico and the Caribbean, and as eurygnathus down the Atlantic coast of South America to Argentina, wintering south to Brazil and Peru. A handful of birds of the American form have been accepted in Europe, with the Azores by far the most likely landfall; mainland claims routinely spend years in assessment.

• Resident
• Breeding (summer)
• Winter
• Passage
• Migration direction
• dark = core range, pale = thinly spread

Where and when to look

From April to September a Wadden sea wall or a tidal inlet on a falling tide is the best spot: birds pass back to the colony with a sandeel held crosswise in the bill. In July or August sit on the beach and find the begging juveniles: that is the easiest moment to study juvenile plumage and the adult head at leisure. On September and October seawatches parties pass low along the coast, when the stiff beat and the pale, almost white upperwing stand out against grey water.

Conservation status

Not globally threatened, but the species is vulnerable because so many birds concentrate in so few colonies. In 2022 highly pathogenic avian influenza tore through the Dutch and German colonies, killing thousands of adults and locally reducing breeding success to almost nothing; numbers have recovered only partly since. Disturbance, the flooding of low-lying colonies and sandeel availability add to the pressure, which is why the Dutch population is Red-listed.