Albatros à tête grise

Identification

The grey-headed albatross averages 81 cm (32 in) in length and 2.2 m (7.2 ft) in wingspan. Weight can range from 2.8 to 4.4 kg (6.2 to 9.7 lb), with a mean mass of 3.65 kg (8.0 lb). It has a dark ashy-grey head, throat, and upper neck, and its upper wings, mantle, and tail, are almost black. It has a white rump, underparts, and a white crescent behind its eyes. Its bill is black, with bright yellow upper and lower ridges, that shades to pink-orange at the tip. Its underwings are white with a lot of black on the leading edge and less on the trailing edge. Juveniles have a black bill and head and a darker nape. Its eye crescent is indistinct and its underwing is almost completely dark.

Taxonomie

Mollymawks are a type of albatross that belong to the family Diomedeidae from the order Procellariiformes, along with shearwaters, fulmars, storm petrels, and diving petrels. They share certain identifying features. First, they have nasal passages that attach to the upper bill called naricorns, although the nostrils of an albatross are on the sides of the bill. The bills of Procellariiformes are also unique in that they are split into between seven and nine horny plates. Finally, they produce a stomach oil made up of wax esters and triglycerides that is stored in the proventriculus. This is used against predators as well as an energy rich food source for chicks and for the adults during their long flights. They also have a salt gland situated above the nasal passage that helps desalinate their bodies, to compensate for the ocean water they imbibe. It excretes a concentrated brine from the nostrils.

Nom scientifique

Thalassarche chrysostoma

Autorité

(Forster, JR, 1785)

Ordre

Procellariiformes

Famille

Diomédéidés

Genre

Thalassarche

Répartition et habitat

Grey-headed albatrosses nest in colonies on several islands in the Southern Ocean, with large colonies on South Georgia in the South Atlantic, and smaller colonies on Islas Diego Ramírez, Kerguelen Islands, Crozet Islands, Marion Island, and Prince Edward Islands in the Indian Ocean, Campbell Island and Macquarie Island south of New Zealand, and Chile. While breeding, they will forage for food within or south of the Antarctic Polar Frontal Zone. Birds that roost in the Marion Island area forage for food in the sub-tropical zone. Juveniles or non-breeding adults fly freely throughout all the southern oceans, north to 35°S.

Aire de reproduction

SO : subantarctic islands of Ildefonso and Diego Ramirez (sw of Tierra del Fuego), South Georgia, Prince Edward, Crozet, Kerguelen (sw to se Indian Ocean), Macquarie (far se of Australia) and Campbell is. (s of South I., New Zealand)

Aire hors reproduction

s oceans mostly s of Subtropical Convergence

Migration

Complete migrants

Comportement

At sea the grey-headed albatross is highly pelagic, more so than other mollymawks, feeding in the open oceans rather than over the continental shelves. They feed predominantly on squid, taking also some fish, crustacea, carrion, cephalopods, and lampreys. Krill is less important as a food source for this species, reflecting their more pelagic feeding range. They are capable of diving as deep as 7 m (23 ft) to chase prey, but do not do so frequently.<p>A single egg is laid in a large nest, typically built on steep slopes or cliffs with tussock grass, and incubated for 72 days. Studies at South Georgia's Bird Island have shown that the growing chick is fed 616 g (21.7 oz) of food every 1.2 days, with the chick increasing in weight to around 4,900 g (170 oz). Chicks then tend to lose weight before fledging, which happens after 141 days. Chick will generally not return to the colony for 6–7 years after fledging, and will not breed for the first time until several years after that.[citation needed] If a pair has managed to successfully raise a chick it will not breed in the following year, taking the year off. During this time spent away from the colony they can cover great distances, often circling the globe several times.

Conservation

The IUCN classifies this bird as endangered due to rapidly declining numbers in South Georgia which holds around half the world's population. It has an occurrence range of 79,000,000 km2 (31,000,000 sq mi) and a breeding range of 1,800 km2 (690 sq mi), with a population, estimated in 2004, of 250,000. Estimates place 48,000 pairs at South Georgia Island, 6,200 on Marion Island, 3,000 pairs on Prince Edward Islands, 7,800 pairs on Campbell Island, 16,408 pairs in Chile, 84 pairs on Macquarie Island, 5,940 on Crozet Island, and 7,905 on Kerguelen Islands<p>Populations have been shrinking based on different studies. Bird Island numbers have been reduced 20% to 30% in the last 30 years. Marion Island registered 1.75% reduction per year until 1992 and now appears to be stable. Campbell Island has seen reduction of 79% to 87% since the 1940s. Overall, the trends looks like a 30-40% reduction over 90 years (3 generations). Illegal or unregulated fishing in the Indian Ocean for the Patagonian toothfish, Dissostichus eleginoides resulted in 10–20,000 dead albatrosses, mainly this species, in 1997 and 1998. Longline fishing is responsible for other deaths.<p>To assist this species, studies are being undertaken at most of the islands. Also, Prince Edward Islands is a special nature preserve, and Campbell Island and Macquarie Island are World Heritage Sites.

Tendance de la population

declining