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Kerguelen Tern | Sterna virgata
Kerguelenstern | Charrán de las Kerguelen
The Kerguelen Tern is a small, dark grey tern of the sub-Antarctic islands of the southern Indian Ocean. Within the region it breeds only on Marion and Prince Edward, South Africa's islands far to the south-east of the mainland. Unlike most terns, it does much of its feeding over land and fresh water.
Voice
A high, rasping kreek or kee-errr, slightly higher and thinner than the call of Antarctic Tern, and a fast chatter when the colony is disturbed.
Recording: Hichem MACHOUK — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
31–33 cm. In breeding plumage a black cap with a sharply defined white cheek stripe below it; the rest of the body, including the underparts, is fairly dark grey. The rump and tail are grey, not white, and the tail streamers are relatively short. The bill is deep red and rather short and thin, the legs red. In non-breeding plumage the forehead is white and the crown speckled, the underparts become paler and the bill darker. Juveniles are heavily scaled brown and black above, darker than young Antarctic Terns. Flight is fast with rather stiff wingbeats, often low over vegetation.
Confusion species
Antarctic Tern Sterna vittata occurs on the same islands and is the main pitfall. It is larger and paler grey, with a white rump and tail with longer streamers, a heavier bill, and feeds mainly at sea. The grey rear body and grey tail of Kerguelen Tern are the best feature in flight. Arctic Tern Sterna paradisaea occurs there on passage, but in the southern summer it is usually in moult and has a white rump.
Habitat
The coastal zone of the islands: marshy grassland, moss flats, freshwater pools and sheltered kelp-filled bays. Much food is taken over land, where it picks insects, larvae and other invertebrates from vegetation and pools, as well as small fish and crustaceans from the kelp zone. It nests in small, loose groups on the ground among low vegetation or on bare gravel near the shore.
Where the bird is most at home, classified by the vegetation units of southern Africa.
Range and movements
Within the region only on the Prince Edward Islands (Marion and Prince Edward), where a few tens of pairs breed; not reliably recorded on the African mainland. Beyond the region it breeds on the Crozet Islands and Kerguelen, with a few pairs on Heard Island. Outside the breeding season the birds largely stay near the breeding islands.
How and when to look
Seen only during the annual relief voyages to Marion, usually in April–May, or during research work on the island. With every tern on the island, check the colour of rump and tail: grey points to this species, white to Antarctic Tern. Eggs are laid in the southern spring and summer, mainly October–December.
Conservation status
Sensitive; globally it is listed as Near Threatened because of its small population of a few thousand pairs on a handful of islands. Introduced cats and rats have done much damage elsewhere; on Marion the cats were eradicated in the early 1990s, but mice, which can attack chicks and eggs, remain.
Scientific name
Sterna virgata | Cabanis, 1875
Cabanis described the species in 1875 and placed it straight away in the genus where it still stands. The genus Sterna was introduced in 1758 by Linnaeus. Sterna goes back to Old English stearn, which appears in the poem The Seafarer; the Frisians used a related word for terns. virgata is Latin for 'striped'; what the name refers to on the bird is unclear. The specimen the first description was based on came from Kerguelen Islands.