Kerguelen Tern Sterna virgata Scientific name definitions

33 cm; wingspan 71 cm. Forehead to nape black; upperparts, including uppertail-coverts, smoky grey, with contrasting white rump; outer tail streamers grey, tail greyish; smoky grey below , becoming white on undertail-coverts; white cheek  and moustachial area contrasts strongly with grey chin and throat; grey underwing-lining diagnostic, and narrow black trailing edge of primaries ; at rest tail does not extend beyond folded wing; bill deep red; feet bright orange (Crozet Is) to dull red (Kerguelen). Separated from S. vittata by slightly smaller size, with shorter bill and wings, darker plumage, and grey, rather than white, uppertail and underwing-coverts. Non-breeding adult has bill dull reddish (Crozets) to black (Kerguelen); birds acquire white forehead by Feb, moult beginning during incubation. Juvenile like that of S. vittata, finely vermiculated grey, brown and buff, with broad pale and dark bars.

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Non-breeders remain close to breeding areas throughout year.

S Indian Ocean close to Antarctic Convergence at Kerguelen Is, Prince Edward and Marion Is, and Crozet Is; reported breeding on Heard I erroneous; sympatric with S. vittata, but diffe­rent phenology and feeding niche. Non-breeders remain close to breeding areas throughout year.

Fish, crustaceans, molluscs, earthworms, insects and spiders. Diet changes seasonally from mainly crustaceans in Sept, fish in Nov, insects in Dec, to fish in Jan–Feb. In courtship feeding, small fish 50%, crustaceans 14%, insects 36%. Chicks fed mainly on spiders, insects, crustaceans, molluscs and earthworms, at period when S. vittata has arrived and is feeding mainly on fish. Feeds alone, or in flocks of up to 20 or more. Fish caught by aerial contact-dipping (83%) and plunge-diving, in inshore waters and around kelp (Macrocystis); sometimes walks on kelp to capture invertebrates. Amphipods taken by wading in tide pools. Inland flocks of up to 50 birds feed on insects snatched from vegetation in flight (90%), or by walking. High winds frequently interfere with feeding.

Calls include a harsh "chittick" and a long drawn out "keeeaaar".

Not globally threatened. Currently considered Near Threatened, and previously, Vulnerable. The global population has been estimated at 3,500–6,500 individuals (1 Jouventin, P., Stahl, J.C. and Weirmerskirch, H. (1988). La conservation des oiseaux des Terres Australes et Atlantiques Françaises. Pp. 225-251 in: Thibault & Guyot (1988). Close , 2 Taylor, M., F. Peacock, and R. M. Wanless (2015). The 2015 Eskom Red Data Book of Birds of South Africa, Lesotho and Swaziland. BirdLife South Africa, Johannesburg, South Africa. Close ). There are no recent counts from the Kerguelen Islands, where most nest (race virgata); 1000–2000 pairs during 1982–1985. The population of race mercuri comprises around 100 pairs on Marion Island in the Prince Edward archipelago (but apparently it no longer nests on Prince Edward Island) and 150–200 pairs on the Crozet Islands.

Population trends are unknown but it is assumed that the species is not undergoing any significant decline. The principal threat to this species is probably from adverse weather conditions, gale-force winds preventing all feeding in marine and terrestrial habitats; the timing and length of the laying season are also dependent on the weather with birds known to desert breeding colonies during storms (3 Weimerskirch, H. and Stahl, J.C. (1988). The breeding and feeding ecology of the Kerguelen Tern Sterna virgata. Ornis Scandinavica. 19: 199-204. Close , 4 Sagar, P.M. (1991). Aspects of the breeding and feeding of Kerguelen and Antarctic Terns at the Kerguelen Islands. Notornis. 38: 191–198. Close ). There are feral cats on Kerguelen but this species inhabits predator-free islets around the main island. The decline of the small population of Prince Edward Island since 1984 may have some connection with the increase in the skua population there, although the principal prey of the latter is burrowing petrels (5 Whittington, P.A., Crawford, R.J.M., Dyer, B.M. and Ryan, P.G. (2009). Estimates of numbers of Kelp Gulls and Kerguelen and Antarctic Terns breeding at the Prince Edward Islands, 1996/1997 – 21361368/21361369. African Journal of Marine Science. 31(3): 439–444. Close ). Salmonid fish introduced into Kerguelen rivers may have provided an additional food supply.