provided by EG-BAMM, Jeroen CS Creuwels & Øystein Varpe
The Antarctic petrel is a medium-sized petrel with a dark brown and white plumage. The dark brown parts may fade during the breeding season to pale brown. Head, neck and back are chocolate brown. Bill is very dark to black. The upperwing is dark brown with a large white bar over the secondary and first primary feathers, which is visible in flight. The underwing and belly are largely white. The sexes are alike, although males are slightly larger. The weight of adult birds fluctuates throughout the year between 550-800g, with peak weight around egg laying.
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Antarctic Petrels have breeding colonies in the coastal zone of Antarctica and in inland Antarctica between 65° and 80°S. As of 1999, there are 35 known breeding colonies; all except one are situated in East Antarctica. The majority of the birds breeds in inland Antarctica (Dronning Maud Land) with colonies situated on nunataks hundreds of kilometres away from the sea-ice border. Colonies are found at altitudes up to 1600 m. At sea, Antarctic Petrels are generally associated with pack ice year-round: in summer normally south of 62°S and in wintertime they can be seen up to 48°S. At sea, Antarctic Petrels are often found foraging together in large flocks or sitting on icebergs, regularly with other fulmarine petrels (often Snow Petrels). In summer, they are foraging in open waters, but can also be seen in areas with pack-ice. Breeding birds may have to forage far from the colony, hundreds to 1000 kilometres away, particularly early in the season when nearby waters tend to be ice covered. In winter, as the sea-ice grows, they move further north, but tend to remain in the vicinity of the sea ice.
The breeding biology of the Antarctic petrel is extremely synchronous; during laying, hatching and fledging most individuals are synchronized within a one week period. Antarctic Petrels lay one egg and do not relay. Individual birds return to the same nest each year, but occasionally they skip a breeding season. Birds generally return to the same partner and pair bonds are long-lasting, but divorces do occur. Antarctic Petrels are philopatric, which means that many return as a (sub)adult to their own native colony. Their age upon return or when they start breeding is not known. Longevity has not been estimated, due to lack of data, but it is expected that individuals may live up to 50 years old. In the colonies, adults are rarely taken by giant petrels or skuas. Abandoned eggs and young chicks, however, are vulnerable and heavily predated by skuas. Older chicks and adults are able to defend themselves against predators by spitting stomach oil. In addition, snow storms during the incubation or chick period may cause high mortality of eggs and chicks.
The Antarctic Petrel colonies are located on snow-free areas such as cliffs, ridges, slopes, but also on relatively levelled areas. The colonies are often facing north to catch as much sunlight as possible and are relatively exposed to the wind preventing the snow to accumulate. Colonies can be large (>10.000 sites) and one inland colony (Svarthamaren, Dronning Maud Land) consists of more than 200.000 breeding pairs, but also several smaller colonies (10s-100s of sites) exist. Normally the nests are densely packed, but sometimes they are located more scattered. The nest consists of a shallow depression and is lined with some gravel or feathers, if material is available. Some nests are well sheltered by boulders and rocks, creating cave like conditions for some birds, whereas other nests have no or limited shelter. There is some risk of melt water accumulating in the nests, a problematic situation for the chick, and a risk that seems to be highest in the well sheltered nests.
Compared to other fulmarine petrels, Antarctic Petrels have long foraging trips (lasting more than two weeks during the incubation period). Birds from colonies close to open water in coastal Antarctica also have foraging trips that last long. Antarctic Petrels take a variety of prey species, depending on season and area. The main prey species are fish (Pleuragramma antarcticum, Electrona antarctica), Antarctic Krill (Euphausia superba) and various squid species. Antarctic petrels take their food from the surface and up to 1.5m deep. When sitting on the water they catch their prey by surface-seizing and surface-plunging. They also dive from air, and use pursuit-plunging, especially around sea-ice edges.
The first adults arrive in the colony in the beginning of October, and the nest sites in the colony gradually become occupied. Like other fulmarine petrels, both parents leave the colony for a pre-laying exodus (late October to second half of November). This exodus is very pronounced in the Antarctic petrel. For about two to three weeks the colony is deserted. Egg-laying takes place in late November, upon the return from the exodus, and eggs are incubated for about 47 days. Parents alternate incubation shifts, and the duration of each shift declines strongly over the breeding season. The male is responsible for the first and longest shift, lasting 2-3 weeks. Chicks hatch around the second week in January. Chicks need protection from the harsh weather and from predators, and are, therefore, guarded by their parents for 7-15 days after hatching. The parents share this duty, and the guarding period consists of 3-4 guarding shifts. Parents in poor condition leave the chick earlier, with the risk of increased chick mortality. Chick fledging commences in late February. The full breeding cycle, from egg-laying until the chick fledges, takes approximately three months. Antarctic Petrels delay the moult of the primaries until the end of the chick-rearing phase. Moulting birds can be seen from the second week of February onwards. Failed birds may start moulting earlier, but also leave the colony earlier.
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