Antarctic Tern

The Antarctic tern (Sterna vittata) is a medium-sized seabird, a member of the family Laridae. It is a robust bird, with a length of 35 to 40 cm and a wingspan of 74 to 79 cm. The weight of this tern ranges between 150 and 180 grams, with a tendency to be heavier during the winter months.

Identification Tips

In its breeding plumage, the Antarctic tern sports a light grey body and wings, complemented by a deeply forked white tail and lower back. A distinctive black cap extends from the nape to the bill, encompassing the brownish-black eyes. The bill, legs, and feet are a striking bright red. During the non-breeding season, the black cap recedes to the area behind the eyes, the underparts lighten, and the bill dulls to a reddish-black. Juveniles display a mottled appearance with yellowish-brown, grey, and white spots on their backs, and a yellowish-brown belly and breast. Their bill is dull black, and the legs are a muted red.

Habitat

The Antarctic tern favors rocky environments, such as islets and cliffs, sometimes amidst other seabird colonies. It nests on cliffs and rocky beaches, avoiding areas accessible to predators like cats or rats, and steering clear of sea lion-occupied beaches.

Distribution

This species has a broad distribution across the southern oceans, including the Antarctic mainland and surrounding sub-Antarctic islands. It is also known to visit South African shores outside the breeding season.

Behaviour

The Antarctic tern is a non-migratory bird, unlike its Arctic counterpart. It remains in proximity to its breeding islands year-round, with southern populations moving slightly northward after breeding. It is a gregarious feeder, often forming flocks when hunting for fish and crustaceans.

Song & Calls

The Antarctic tern is vocally active around roosts, with a primary call of "trr-trr-kriah" during flight or fishing. It uses a "chrrrr" sound to defend nests and a higher-pitched call to attract mates.

Breeding

Breeding occurs from November to December, with variations due to climate and food availability. The terns nest in loose colonies or as isolated pairs, laying one or two eggs that are incubated for 23 to 25 days. Chicks hatch in the summer and are fed by parents for 27 to 32 days until they develop flight feathers.

Similar Species

The Antarctic tern is often confused with the Arctic tern, which has shorter legs and more pronounced black margins on primary feathers. The white-fronted tern is also similar but can be distinguished by its larger size, lighter colors, and longer black bill.

Diet and Feeding

The Antarctic tern is an opportunistic feeder, primarily consuming small fish and crustaceans like Antarctic krill. It employs plunge diving or bill submersion strategies to catch prey, often foraging near the shore in kelp zones.

Conservation status

The IUCN Red List categorizes the Antarctic tern as Least Concern, with a stable global population estimated between 132,000 and 145,000 individuals. However, some breeding failures have been attributed to introduced predators such as cats and rats.