Present situation of population of the Snowy Sheathbill near south border of the breeding range. - S.A. Loparev. - Berkut. 10 (1). 2001. P. 91-101.
Data were collected during wintering on Ukrainian antarctic station “Vernadsky” (island of Galindez near the northern part of the Antarctic peninsula, 65.15 S, 64.16 W) in season 2000/2001. Biology of the Sheathbill, relations with other species, influence of abiotic factors were studied in environs of the station. Though the Snowy Sheathbill has the large breeding range, it is one of the most unnumerous antarctic birds. Total number does not exceed several thousandsv individuals. Southern border of the breeding range passes in the surveyed territory. About 100 sheathbills were found here. On Argentine Islands the species is present the whole year round, but in April the appreciable increase of number is observed. Migration passes during April and May. By the end of May is formed wintering group in 14-20 birds. Adult individuals make basis of such groups. Pairs are remained during the whole year. Places of permanent exits of Gentoo Penguins and Adelie Penguins on a coast and ice, sealeris are the main wintering habitats. They provide birds with a forage: indigested remains of creel and other Crustacea. Sheathbills constantly visit also thrown out food remains on antarctic stations. Foraging behaviour in winter is desrcibed. Spring display beginns sometimes in Julay (old pairs), mass display occurs since end of August till end of September. Snowy Sheathbills nest in colonies of Blue-eyed Cormorants, Gentoo Penguins or Bearded Penguins. Colonies of Adelie Penguins are unattractive because of aggressiveness of these birds, especially near nests. Lost belch of cormorants and peguins, mainly from Crustacea, is the main food of sheathbills and their chicks during the breeding period. More seldom these birds pick up regurgitated remains of fish. Eggs of penguins, dead chicks and carrion are also present in ration, but they are not an essential part of it. Sometimes sheathbills independently prey on Crustacea on a shore. Feeding on carrion in colonies is sharply limited by the presence of skuas. Sheathbills make their nests in niches and caves under big stones. Distance between the nest and feeding plots does not exceed 30-100 m. Nests are made of feathers, panes of skin with feathers, bones, etc. Egg laying begins as a rule in December. Full clutch has 1-3 eggs, as a rule 2 ones. Hatchlings are appeared in first and second ten-days of January. Such late times of breeding are connected with peculiarities of feeding. Penguins feed their chicks, and therefore there are much food. Both parents hatch eggs. First coat of chicks is dark-brown, leggs and bill are blue-black. Chicks in the age of 1-2 days weigh 37-44 g. Breeding success makes 1,6 fledgelings per successful pair or 0,8 ones per breeding pair. Moult of adult birds begins usually in second half of January and ensds mainly till middle of April. Differences between sexual and age groups are described. The Southern Black-backed Gull and the South Polar Skua are the main competitors in feeding. Protection of this vulnerable endemic bird species is necessary. [Russian].
Key words: Snowy Sheatbill, Chionis alba, Antarctic, ecology, breeding, feeding, behaviour, protection.
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