Kerguelen Tern

Kerguelenseeschwalbe (Sterna virgata )

The Kerguelenseeschwalbe (Sterna virgata ) is a type of the tern family. They occur exclusively on sub-Antarctic islands of the Indian Ocean. It is a medium sized, mostly gray tern with a dark head cap.

The IUCN classifies the species as near threatened Kerguelenseeschwalbe ( near threatened ), as the world population is very small overall. The population is estimated at only 3500-6500 mature individuals, but is overall assessed as stable.

Appearance

The Kerguelenseeschwalbe reaches a body length of up to 33 centimeters. The wing length is 24.7 to 27 inches and the wingspan is 68 to 72 centimeters. Until now, there are insufficient biometric data, which show that there are gender-specific differences in size.

The Kerguelenschwalbe is compared with other tern very dark. The tail is forked not very deep and the tail feathers are shorter than is the case with other species of the genus Sterna. The legs are very short. The beak is also relatively short and narrow and bright red. The legs and feet are bright red. Kerguelenschwalben in breeding plumage have a black head cap, which only slightly expands to the back of the neck. A conspicuous broad white line is from the dark head cap from the rest of the body plumage. The body top is smoke gray, the hull is slightly lighter. In Plain dress red beak is colored somewhat dull, the dark head cap is smaller and the forehead whitish. Young birds resemble the adult Kerguelenschwalben in Plain dress, the head cap is somewhat brownish and the plumage is interspersed with brownish spots. The body bottom is brighter than in adult birds.

Distribution area

The Kerguelenseeschwalbe breeds on the Prince Edward Islands, the Crozet Islands and the Kerguelen Archipelago in the southern Indian Ocean. It is predominantly a state bird, who is on the inland waters of these islands. Distribution area are the Kerguelen.

Way of life

The Kerguelenseeschwalbe eats fish, crustaceans, molluscs, worms, insects and spiders. The food composition will vary depending on the season. Their diet they examined predominantly in small flocks of up to twenty individuals. The most common technique of food acquisition is the shock diving. But runs occasionally on floating plants in order to look for invertebrates. Search for food, it uses not only inland waters, on the Prince Edward Islands, they found, for example up to 90 percent of their food on the coast.

The breeding season falls in the period from September to January. It breeds in small, very loose colonies of up to 30 breeding pairs. The nest is a shallow depression, which is often covered with plant material. The nest consists of one to two eggs. These are incubated for 24 days. The newly hatched chicks are brooded for five days. The young birds fledge in age from 31 to 39 days, but are dependent on the supply from the parent birds for 20 days.

The hatching success is very high with 73-88 percent. However, have a very high mortality rate towards the end of the breeding season hatched chicks because of lack of food. The was threatening factors include in particular the large number of feral cats on the Kerguelen.