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Common Tern | Sterna hirundo
Visdief | Charrán común
The Common Tern is one of the most widespread terns of the northern hemisphere. In the guide area it is a passage migrant and winter visitor on both coasts, between its breeding grounds in North America and its wintering grounds as far as South America. Because it closely resembles other terns, careful identification is needed.
Voice
A drawn-out, descending kee-yarr stressed on the first syllable, as well as short kip calls and, when disturbed, a rapid kek-kek-kek.
Recording: Lionel FREDERIC — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
31–35 cm, slender, with narrow wings and a deeply forked tail whose outer feathers do not reach beyond the wingtips at rest. Breeding adults have a black cap, pale grey upperparts, pale grey-washed underparts and a red bill with a black tip; the legs are red and fairly long. On the upperwing the outer primaries form a dark wedge, and from below the primaries have a broad, blurred dark trailing edge; only the inner primaries are translucent. Outside the breeding season, the plumage most seen here, the forehead and underparts are white, a black band runs from the eye round the hindcrown, the bill is mostly black and a dark carpal bar is visible. Juveniles have a brownish scaly back, an obvious dark carpal bar and a pale bill base.
Confusion species
Arctic Tern Sterna paradisaea has shorter legs, a shorter bill and translucent primaries with a narrow, sharp black trailing edge. Forster's Tern Sterna forsteri has silvery-white primaries, a longer tail and, outside the breeding season, an isolated black eye patch instead of a black band round the hindcrown. Roseate Tern Sterna dougallii is paler and whiter, with very long tail streamers and a mostly dark bill. Sandwich Tern Thalasseus sandvicensis is larger, with a yellow-tipped black bill.
Habitat
Coastal waters, bays, lagoons, salt pans, estuaries and harbours, and on migration also large inland lakes; it rests on sandbars, beaches, piers and buoys. It also migrates far offshore over open sea. It fishes by plunge-diving from a brief hover.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
Along the Pacific coast from Baja California to Panama and along the Caribbean coast from Tamaulipas to Panama, most numerous during migration and often in large flocks over the sea. In winter mainly in the south of the guide area, including Costa Rica and Panama. Outside the guide area the species breeds across much of North America, Europe and Asia and winters along the coasts of South America, Africa and southern Asia.
- Winter visitor (c. Oct–Mar)
- dark = core range, pale = thinly spread
How and when to look
Flocks of resting terns on sandbars, piers and salt pans offer the best chance to compare Common Terns with other terns; during autumn migration hundreds sometimes pass along the coast. Leg length, bill tip and primary pattern are decisive.
Conservation status
Not threatened globally. Colonies on the breeding grounds are sensitive to disturbance and predation. In the guide area a passage migrant and winter visitor with no regular breeding population.
Scientific name
Sterna hirundo | Linnaeus, 1758
Linnaeus described the species in 1758 and placed it straight away in the genus where it still stands. He introduced the genus Sterna in that same work. Sterna goes back to Old English stearn, which appears in the poem The Seafarer; the Frisians used a related word for terns. hirundo is Latin for 'swallow', after the forked tail and light build the tern shares with that bird. The specimen the first description was based on came from Sweden.