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Dietary composition of birds, breeding on King George Island

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Three skua specimens with a colouration pattern of the Chilean skua were observed at Potter Peninsula, King George Island, Antarctica. Two of these were breeding birds. However, they showed a pattern of mitochondrial DNA typical for South Polar skua. These birds thus represent hybrids originating from male Chilean skua. The third bird could not be caught. It appeared to be indistinguishable from Chilean skua.
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An analysis of the diet of the Kelp Gull Larus dominicanus during the chick-rearing period at a colony in northern Gerlache Strait, Antarctic Peninsula showed that Antarctic Krill Euphausia superba made up 20% by mass of the diet of the adults and 66% by mass of the chicks' diet. Fish constituted a low proportion of total prey, both in pellets and chick regurgitations, whereas the importance of limpets in adult pellets was similar to results from other studies in Antarctica. Chick regurgitations show substantial differences in the diet at the study site with other localities. Our data on breeding success were in accordance with localities farther south in Antarctica where Kelp Gull chicks are fed offshore prey. Antarctic Krill may represent a substantial resource for Kelp Gulls in some localities as those reported here; the abundance of this resource during the chick-rearing period, associated with low levels of predation by skuas and with favourable local climatic conditions, could be linked with very high reproductive success in the study area.
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This paper is the first methodological investigation of the ligature application for food studies in semi-precocial birds. In a population of Brown Skuas, South Polar Skuas and mixed pairs, ligatures were attached to chicks for a period of 28 hours. Of 408 theoretical sampling visits, 8% could not be carried out. The number of times the ligature was applied did not cause differences in mortality of chicks nor did I find a growth difference for treated and untreated chicks. The method did not work equally well for three skua forms with different diets. Parent birds disgorged food equally often to ligatured and control chicks. This method is probably less accurate when used for diets with a high proportion of fish. While I was applying the ligature, body weight loss showed a non-linear decline, with a drop appearing in the first hours after application. The chicks may compensate for weight loss. In chicks whose stomachs were flushed after ligature use, no food was found, leading to the assumption that the ligature method is highly efficient. A projection of the total food consumption by field data revealed values of only 45% (Brown Skua) and 25% (South Polar Skua) ofthat of the model by Drent and others (1992). The advantages and disadvantages of ligaturing are discussed in regard to its further use in precocial birds.
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A total of 3518 pairs of Antarctic terns nested on King George Island in the 1980/81 season. In the region of Admiralty Bay numbers ranged from 652-1828 pairs (7.2-20.1 pairs per 1 km of coastline). Most pairs nested on rock-rubble heaps void of vegetation and on moraines. On average 1.45 eggs, 0.46 newly hatched chick and 0.22 young bird leaving the colony fell to one pair. First chicks grew faster. The diet of adult and young birds consisted of Euphasia: Amphipoda and fish. The total consumption of krill by Antarctic terns in the region of Admiralty Bay was 4.69-4.93 tons in 1980/81, which makes 0.60-0.78% of its biomass. The presence of tern colonies may be important to the development of associations of nitrophilous lichens.
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During the Dutch King George Island Expedition of 1990/91, complete stomach contents of Pintado or Cape Petrels were sampled by means of the stomach-flushing method. Food samples consisted of Antarctic silverfish Pleuragramma antarcticum by 60% of mass. The remainder of the mass was made up mainly of amphipods and Antarctic krill Euphausia superba. This is in contrast to previous studies of breeding pintado petrels which have reported a diet dominated by crustacean prey with a fish component of less than 30% by mass. -from Authors
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The Pale-faced Sheathbill (Chionis alba) is an opportunistic predator-scavenger. During spring in Antarctica it foraged in colonies of southern elephant seals, obtaining placentas, pup carcasses, milk from nursing cows, blood, and feces. Afterbirths and pup carcasses constituted the bulk of the food consumed. Daily consumption estimates averaged 67 g/bird for placenta and 11 g/bird for pup carcasses, which are 54% and 26% of daily energy requirements, respectively. Sheathbills spent 86% of the day foraging or displaying and 14% resting or preening. Actively feeding birds spent 38% of the time searching for food, 20% feeding, 23% resting, 14% on comfort activities, and 3% in agonistic behaviors.
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In the diet of Phoebetria palpebrata squid and krill Euphausia superba were the main components by weight and by frequency of occurrence, although fish were also taken. P. palpebrata can forage more widely during the breeding season than black-browed albatross Diomedea melanophris and grey-headed albatross D. chrysostoma. Ecological segregation from these is probably achieved by a combination of differences in foraging range and area and by differences in the detailed composition of the diet.-from Author
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A total of 45 pellets from the Imperial Cormorant or Blue-eyed Shag Phalacrocorax atriceps was collected in January 1994 at Duthoit Point, Nelson Island, South Shetland Islands. The analysis showed fish as the main prey, followed by octopods, polychaetes and gastropods. Notothenia coriiceps formed the bulk of the diet, but Harpagifer antarcticus was the most frequent and important fish in number. The prey items represented in the pellets were consistent with those observed in stomach contents sampled simultaneously in the same colony; however, they differed in importance. A daily mean of 0.7 pellets per bird was collected, representing 255 g of fish. Correction factors previously estimated in a feeding trial were applied to this value, and suggested that the average daily amount of food ingested by an adult cormorant during the sampling period was 1325 g, which falls within the range observed by stomach content analysis. Other aspects related to the feeding behaviour of the species are also discussed.
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The first underwater digital photographs obtained by cameras carried by Shags Phalacrocorax aristotelis showed the birds diving in areas dominated by soft coral Alcyonium digitatum and feeding on butterfish Pholis gunnellus, which were brought to the surface before being swallowed. Prey capture rates were markedly lower than previous estimates for birds feeding on sandeels Ammodytes. This reduced foraging performance probably contributed to the very poor breeding success at the colony on the Isle of May in 2005.