All species › Waders, gulls and terns › Skimmers, noddies, terns and gulls › Snowy-crowned Tern
Snowy-crowned Tern | Sterna trudeaui
Trudeaus stern | Gaviotín piquerito | Trinta-réis-de-coroa-branca
The Snowy-crowned Tern is a medium-sized, pale grey tern of southern South America, with a white head and a black eye mask. It breeds in marshes and at lagoons in Argentina, Uruguay, southern Brazil and central Chile. Outside the breeding season birds from Chile move north along the coast; in the guide area it is a rare visitor to the coast of Peru.
Voice
A hoarse, grating kerr, similar to the call of other terns, and short kip calls.
Recording: Meena Haribal — CC BY-NC-SA 4.0 · xeno-canto
Identification
33–36 cm, a medium-sized tern with a fairly long, forked tail. Adults have a white head with a black stripe through and behind the eye, and pale grey upperparts and underparts; the pale primaries and the white rump and tail contrast with the grey body. In breeding plumage the bill is yellow with a black band just before the tip and the legs are orange. Outside the breeding season the bill is duller and darker, with less yellow. Juveniles have brown spots on the upperparts and a darker bill. The sexes are alike.
Confusion species
Forster's Tern Sterna forsteri, a very rare vagrant from the north, has the same type of mask in non-breeding plumage, but white underparts and a black bill. Common Tern Sterna hirundo has in non-breeding plumage a black hindcrown, a dark bar on the forewing and white underparts. South American Tern Sterna hirundinacea is larger, with a red bill and a black cap or hindcrown.
Habitat
Outside the breeding season beaches, river mouths and coastal lagoons, where it dives for small fish at sea and in shallow water. It breeds in colonies in freshwater marshes, at lagoons and on islets in lakes, often with nests on floating plant debris. It does not breed in the guide area.
Where the bird is most at home, classified by the vegetation units of the Andes and the west coast.
Range and movements
In the guide area only in Peru, as a rare visitor along the coast, mainly in the south and centre of the country; absent from Colombia, Ecuador, Bolivia and the Galápagos. Outside the guide area it breeds in central Chile and from southern Brazil through Uruguay to Argentina.
How and when to look
In the southern winter, look among the terns on beaches and at river mouths in southern Peru for a grey tern with a white head and black mask. A masked bird in the northern winter may also be a Forster's Tern.
Conservation status
Least Concern. The population is declining locally through the loss and disturbance of marshes on the breeding grounds.
Scientific name
Sterna trudeaui | Audubon, 1838
Audubon described the species in 1838 and placed it straight away in the genus where it still stands. The genus Sterna was introduced in 1758 by Linnaeus. The genus name comes from Old English stearn, a word for a tern; the Frisians had a similar word. The species name honours James de Berty Trudeau (1817–1887), a physician from Louisiana and friend of Audubon, who sent him the specimen. The specimen the first description was based on came from Great Egg Harbor, New Jersey, United States.