Antarctic tern

Sterna vittata Gmelin, 1789

Order: Charadriiformes

Family: Sternidae

New Zealand status: Native

Conservation status: Recovering

Geographical variation: Five subspecies recognised; New Zealand birds are of the subspecies bethunei.

Antarctic tern. Adult. North East Island, Snares Islands, November 1986. Image © Colin Miskelly by Colin Miskelly

Antarctic tern. Adult. North East Island, Snares Islands, November 1986. Image © Colin Miskelly by Colin Miskelly

The Antarctic tern is the most frequently observed tern around New Zealand’s subantarctic islands. Unlike its northern counterpart, the Arctic tern, New Zealand Antarctic terns do not undertake spectacular migrations after breeding, but is likely to remain close to the breeding islands all year. When feeding on shoals of small fish or swarms of crustaceans they may form flocks of up to 100 birds.

The same species is widely distributed around subantarctic islands of the southern hemisphere, as well as exposed rocky areas of the Antarctic mainland. The more southern populations migrate northwards after breeding e.g., those Antarctic terns that breed on the Kerguelen archipelago overwinter in southern Africa.

Identification

The Antarctic tern is a medium-sized tern with a white rump and forked tail. In breeding plumage adults have a black cap down to a bright red bill, with white cheeks, an even grey body, and wings with black only on the outer edge of the outer primary; the legs are red. In non-breeding plumage the black cap recedes to just behind the eyes, the underparts become white and the bill becomes dull reddish-black. Juveniles initially are marked buff, grey and white on the back, with markedly buff flanks; the bill is dull black and the legs are dull red.

Voice: “trr-trr-kriah” is the main call when in flight and fishing. A “chrrrr” is given when defending its nest against intruders, and a high-pitched call is used to summon their mate

Similar species: most likely to be confused with migrant Arctic terns. The latter are usually in non-breeding plumage when adult Antarctic terns are in breeding plumage. Arctic terns usually are shorter-legged and have more extensive dark markings on the outer edge of the outer primaries than do Antarctic terns. In addition, immature Arctic terns have a marked dark carpal bar, which is absent in Antarctic terns.

Antarctic terns can co-occur with white-fronted terns at The Snares, Auckland  and Campbell Islands. The latter are larger, paler, and have a longer, fine, black bill than Antarctic terns in any plumage.

Distribution and habitat

Antarctic terns breed at all New Zealand subantarctic islands, plus on some of the muttonbird islands off southern Stewart Island. During the breeding season (September-April) Antarctic terns do not range far at sea, and so are usually seen within 2 km of the breeding islands. At the northern breeding sites (islands off Stewart Island, The Snares), adults and young usually stay in nearby coastal waters, but farther south they tend to be absent April-October. They are assumed to be out in the southern ocean, as Antarctic terns have not been recorded north of Foveaux Strait.

Population

An estimated 1000 breeding pairs, but no systematic surveys completed except at The Snares where a minimum of 65 breeding pairs were present during the 1980s.

Threats and conservation

Populations on many breeding islands, such as The Snares and Campbell Islands, are secure in the absence of introduced mammalian predators. On the Antipodes mice may affect breeding success. On Auckland Island feral cats, pigs and mice are likely to affect breeding success and to prey upon adults and young.

Breeding

Antarctic terns are usually colonial breeders, although they may also nest as isolated pairs or small groups. Nests may be on bare rocky or gravel areas, or among light vegetation such as tussock or small Hebe. The laying season is prolonged and varies from island to island. For example, it is September-March at The Snares, October-March at Campbell Island, December-March at the Antipodes, and November-February at the Auckland Islands. The nest is a shallow scrape or depression, usually lined with flattened vegetation. The clutch size is typically 1-2. Both members of the pair incubate the eggs and feed the young.

Behaviour and ecology

Antarctic terns feed close inshore, either singly or in flocks, catching prey by contact dipping (i.e. submerging the bill whilst flying) or plunge diving to become completely submerged. Single birds may defend a feeding area, chasing off conspecifics whilst uttering a loud “chrrrrrr”. During the breeding season they defend the nest site against any intruders by repeated dive bombing, occasionally striking them with their sharp bill. After the breeding season, Antarctic terns tend to form flocks at well-established roosts on rocky promontories adjacent to the sea. The age of first breeding is 3 years and with an estimated annual survival of 94% the average life-span is 17 years, with the oldest birds surviving over 30 years.

Food

Small fish and crustaceans.

Websites

http://www.birdlife.org/datazone/speciesfactsheet.php?id=3272

References

Bailey, A.M.; Sorensen, J.H. 1962. Subantarctic Campbell Island. Proceedings of the Denver Museum of Natural History 10.

Heather, B.D.; Robertson, H.A. 1996. The field guide to the birds of New Zealand. Viking, Auckland.

Higgins, P.J.; Davies, S.J.J.F. 1996. Handbook of Australian, New Zealand and Antarctic birds. Vol. 3, snipe to pigeons. Oxford University Press, Melbourne.

Sadleir, R.F.M.; Taylor, R.H.; Taylor, G.A. 1986. Breeding of Antarctic terns (Sterna vittata bethunei). Notornis 33: 264-265.

Sagar, P.M. 1978. Breeding of Antarctic terns at the Snares Islands, New Zealand. Notornis 25:59-70.

Sagar, P.M. 1991. Aspects of the breeding and feeding of Kerguelen and Antarctic terns at the Kerguelen Islands. Notornis 38: 191-198.

Sagar, P.M.; Miskelly, C.M.; Sagar, J.L.; Tennyson, A.J.D. 2003. Population size, breeding, and annual cycle of the New Zealand Antarctic tern (Sterna vittata bethunei) at the Snares islands. Notornis 50: 36-42.

Sagar, P.M.; Miskelly, C.M.; Scofield, R.P.; Sagar, J.L. 2007. Survival estimates of Antarctic terns (Sterna vittata bethunei) on the Snares Islands, New Zealand. Notornis 54: 214-219.

Sagar, P.M.; Sagar, J.L. 1989. The effects of wind and sea on the feeding of Antarctic terns at the Snares Islands, New Zealand. Notornis 36: 171-182.

Recommended citation

Sagar, P.M. 2013. Antarctic tern. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Antarctic tern

Social structure
monogamous
Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Nest type
scrape
Nest height (mean)
0 m
Maximum number of successful broods
2
Clutch size (mean)
1-2
Mean egg dimensions (length)
46 mm
Mean egg dimensions (width)
32 mm
Egg colour
Buff-olive with brown and black blotches
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Incubation behaviour
shared
Incubation length (mean)
24-25 days
Nestling type
altricial
Age at fledging (mean)
27-32 days
Age at fledging (min)
27 days
Age at fledging (max)
32 days
Age at independence (mean)
Unknown
Age at first breeding (typical)
3 years
Maximum longevity
>30 years
Maximum dispersal
Unknown

New Zealand Antarctic tern

Breeding season
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun
Egg laying dates
  • Jul
  • Aug
  • Sep
  • Oct
  • Nov
  • Dec
  • Jan
  • Feb
  • Mar
  • Apr
  • May
  • Jun