Antarctic tern (Sterna vittata)
|Size||Length: 35 - 40 cm (2)|
Wingspan: 74 - 79 cm (2)
Average summer weight: 167 - 170 g (2)
Average winter weight: 197 - 205 g (2)
The Antarctic tern is classified as Least Concern (LC) on the IUCN Red List (1).
The Antarctic tern (Sterna vittata) is a small seabird that is distributed throughout the southern hemisphere. In breeding plumage, the Antarctic tern has a black forehead, extending to the crown and back of the neck. The upperparts of the body are pale grey, contrasting with the white rump and white forked tail, and the underparts are generally grey-white, with white undertail coverts. The eyes are brownish-black and the bill and legs are bright red (2) (3).
The non-breeding adult Antarctic tern appears similar, but the forehead is white and the crown is streaked with white. The underparts are whiter outside of the breeding season, and the bill and legs vary from reddish-black to dull red (2) (3).
The juvenile Antarctic tern typically has a white forecrown, streaked with black, and a dark brownish-grey to blackish-grey hindcrown. The upperparts are typically grey with heavy black and buff bars, and white on the underparts with fine black barring. The feathers of young juvenile Antarctic terns usually have scaly dark tips, but these wear quickly and are not present in older juveniles. Year-old juveniles have a white forehead, similar to the breeding adult, as well as white underparts and a dull reddish-black bill (2).
Six subspecies of the Antarctic tern are recognised, which vary in their distribution, size and plumage tone. Sterna vittata gaini is the largest, and also palest, of the subspecies, followed by Sterna vittata tristanensis. Sterna vittata georgiae is the smallest of the six subspecies, but has the longest wings, while Sterna vittata vittata, Sterna vittata bethunei and Sterna vittata macquariensis are all intermediate in size. The nominate subspecies, Sterna vittata vittata, has the darkest plumage (2).
The Antarctic tern breeds on a large number of sub-Antarctic islands in the Southern Oceans and off the coast of Antarctica (1) (4) (5). It winters on the coast of Argentina and South Africa (4) (6) (6), particularly along the coastline and offshore islands of the Western and Eastern Cape provinces of South Africa (7).
During the breeding season, the Antarctic tern inhabits rocky islands or rocky areas near the coast. It generally nests in areas inaccessible to predators, including offshore stacks and cliffs, among boulders, on headlands, stacks, ridges, spits and peninsulas, as well as on gravely, rocky and sandy beaches and in sparse scrub (2) (4). The nest is typically placed in a natural depression in rock, or in a shallow scrape in soil, sand or vegetation (4).
The Antarctic tern forages in inshore waters during the breeding season, in coves, bays, inlets, harbours and estuaries, especially where there is an abundance of kelp (4).
Outside of the breeding season, the Antarctic tern is primarily pelagic, roaming over large areas of open water. It often forms communal roosts on ice-floes or icebergs in Antarctica, and will forage in open water bordering the edge of the ice (2) (3) (4). The Antarctic tern also winters off the temperate coasts of South America and South Africa, where it generally inhabits rocky headlands and beaches (2) (4).
The Antarctic tern feeds almost exclusively on small fish, but it may also take small quantities of molluscs, crustaceans, insects and algae (2) (4). The Antarctic tern typically feeds alone or in small flocks (2) (4), although it may fish in flocks of up to several hundred birds where prey is abundant (3). It forages by hovering 2 to 15 metres above the water, before dipping or plunge-diving below the surface of the water in pursuit of prey (2) (3) (4).
Breeding usually begins around November and December, although the exact timing varies with location, climate and food availability (2) (4). On Heard Island, for example, egg-laying occurs between October and January (3), on Marion Island and the Crozet Islands between December and February, and between February and March in the Antipodes (2). The Antarctic tern forms loose breeding colonies of around 5 to 20 pairs, but pairs will also nest alone or, more rarely, in large flocks of up to 1,000 pairs (2) (3) (4). Generally, 1 or 2 eggs are laid, and are incubated by both adults for 23 to 25 days (2) (5). The young Antarctic terns typically leave the nest and hide 3 or 4 days after hatching (5), although they are unable to fly until they fledge at 25 to 32 days old (2) (5). The young Antarctic terns are fed and cared for by the adults for some time before they become independent (3) (5). Adult Antarctic terns often cooperate to defend the colony from predators such as skuas and gulls, which may take eggs or chicks from unattended nests (2) (3).
The Antarctic tern is migratory, typically travelling long distances from its breeding grounds to winter off the coasts of South America and South Africa. Populations wintering in South America typically arrive from mid-April, and remain until mid-October (4). In South Africa, wintering Antarctic terns arrive in April and May, although individuals continue to arrive through to August. Generally, most terns depart for the breeding grounds in September and October, although some isolated individuals do remain during the summer months (7). Similarly, some populations of the Antarctic tern remain close to the breeding grounds all year round (4).
Although the Antarctic tern is not currently considered globally threatened, many islands support only tiny populations of this species and some subspecies may therefore be extremely vulnerable to localised extinctions (2) (3).
Ground-based predators, such as rats, as well as feral and domestic cats, feed on the eggs, chicks and adults of the Antarctic tern (2) (3) (8). Predation by these introduced species is likely to have been one of the main causes of population declines on many islands, and in Tristan da Cunha the Antarctic tern is now restricted to the remaining rat-free islands within the group (8). Rats are thought to be the primary cause of this species’ failure to breed on the main island at Macquarie Island (3).
The Antarctic tern is also particularly vulnerable to human disturbance, which is known to cause frequent reproductive failures in this species (2) (3) (4).
The Antarctic tern is listed on Annex II of the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), which aims to protect bird species which are dependent on wetlands for at least part of their annual cycle. The agreement prohibits the taking of birds and eggs, deliberate disturbance to populations, and the possession or utilization of, and trade in, birds or eggs of species listed by the agreement (9).
On Macquarie and Heard Islands, the Australian Government has made a number of recommendations to ensure that subspecies of the Antarctic tern breeding in these areas are protected. These include monitoring the breeding population size and breeding success on Macquarie Island and Heard Island, eradicating feral pests to lessen predation of eggs and chicks, ensuring that effective quarantine programmes on the islands minimise the introduction of further pests, and managing tern colonies to minimise human disturbance (3).
Find out more about the conservation of the Antarctic tern and other birds:
BirdLife International - Antarctic tern:
Find out more about conservation in the Antarctic region:
Polar Conservation Organisation:
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- Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- Coverts: small feathers concealing the bases of larger flight feathers, usually on the wings or tail.
- Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
- Feral: previously domesticated animals that have returned to a wild state.
- Incubate: to keep eggs warm so that development is possible.
- Molluscs: a diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
- Nominate subspecies: the subspecies indicated by the repetition of the specific name. Thus, in this case the Cyclura nubila nubila is the nominate subspecies of the Cayman Islands ground iguana, Cyclura nubila.
- Pelagic: in birds, applied to sea birds that come to land only to breed, and that spend the major part of their lives out at sea.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Temperate: referring to the geographical region that lies between the polar and tropical regions, characterised by a moderate climate with distinct seasons.
IUCN Red List (March, 2011)
- del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
Department of the Environment and Heritage. (2005) Ten Seabird Species Issues Paper. Part B: Conservation Issues for Specific Species/Groups - 4. Antarctic Tern (New Zealand) and Antarctic Tern (Indian Ocean) - Conservation issues. Department of the Environment and Heritage, Australian Government. Available at:
BirdLife International - Antarctic tern (March, 2011)
Polar Conservation Organisation - Antarctic tern (March, 2011)
Avian Demography Unit - Antarctic tern (March, 2011)
- Tree, A.J. and Klages, N.T.W. (2004) Population size, distribution and origins of Antarctic Terns Sterna vittata wintering in South Africa. Marine Ornithology, 32: 55-61.
Agreement on the Conservation of African-Eurasian Migratory Waterbirds (March, 2011)