Antipodean tern

Sterna vittata

 The Antipodean tern (Sterna vittata), also called fork-tailed tern or Antarctic tern, is a species of tern that occurs around the Antarctic. The name comes from the antipodes, which according to earlier beliefs should colonize the "underside" of the earth. Several subspecies are distinguished. The IUCN classifies the antipodean tern as harmless (least concern) because of its very large distribution area.

The antipodean tern reaches a body size between 32 and 40 centimeters. The wing length is between 23.6 and 28.7 centimeters and the wingspan is 74 to 79 centimeters. Antipodean terns weigh between 114 and 205 grams, and males tend to have slightly longer bills than females.

The antipodean tern is thus a medium-sized species of tern. It is drawn in gray and white and has a black head cap that extends down to the neck. Most individuals have a white stripe on the cheeks that separates the dark head cap from the light gray underside of the body. The top is blue-gray. The under tail-coverts are white. The color of the beak and legs varies depending on the subspecies from a dark coral red to a bright red. In the plain dress, the forehead is white, the underside of the body is spotted gray. The legs are usually a little more dull and brownish.

The antpode tern can be confused with a number of other terns. The resemblance to the Falkland tern, the Kerguelen tern, the Arctic tern and the common tern is particularly pronounced.

The antipodean tern has a very large distribution area. It breeds on Tristan da Cunha, Gough Island, Bouvet Island, Crozet Islands, Kerguelen, Amsterdam Island, Heard Island, Macquarie Island, Campbell Island, Auckland Islands, Snare Islands, Antipode Islands and the Bounty Islands. On the Antarctic Peninsula it breeds up to latitude 68 south. The breeding area also includes the South Shetland Islands, the South Orkney Islands, South Georgia and the South Sandwich Islands.

The antipodean tern feeds on fish as well as krill and other crustaceans. During the breeding season it also uses inland waters for foraging. In winter quarters, however, they only find their food in the sea. Typical for them is a shock dive from a height of ten meters. It looks for food both individually and in small schools. Occasionally it also follows boats and adult birds occasionally forage for food on the mainland as well. On Tristan da Cunha she can occasionally be seen looking for food in pastures.

The breeding season depends on the geographical latitude, the breeding season usually falls between October and March. It is basically a colony breeder and usually breeds in small colonies of five to 40 pairs. However, there are individual breeding colonies that comprise 1000 breeding pairs. Antipodean terns breed on islands with terrestrial predators, but also individually on inaccessible cliffs. The nest is a shallow hollow, often lined with shells or small stones. The clutch consists of one or two eggs. These are incubated for 23 to 25 days. The young birds can fledge at 27 to 32 days, but are still fed by the parent birds for a few days afterwards.

The current population is estimated by the IUCN at 130,000 to 140,000 sexually mature individuals. [6] Basically, antipode terns are sensitive to human disturbance. A population-threatening factor for this species is the introduction of terrestrial predators, including the introduction of domestic cats to their breeding islands. The small breeding population on Macquarie Island, for example, is threatened with extinction because cats and rats eat adult birds as well as chicks and eggs there.