Description: At the sub-Antarctic island of South Georgia 25 of the 29 breeding species are seabirds. Fifteen of these have recently been studied in some detail. By examining the timing of their breeding seasons and their diet and feeding ecology (especially feeding techniques and potential foraging ranges), the nature of their ecological isolating mechanisms, and in particular the way in which they partition the resources of the marine environment, are reviewed. Although breeding season adaptations occur (winter breeding in Wandering Albatross and King Penguin; out of phase breeding in two species-pairs of small petrels) these are less important than dillerences in food and feeding ecology. There is a fundamental distinction between the niche of pursuit-diving species (mainly penguins) and the remainder which are basically surface-feeders. The two abundant krill-eating penguins show clear differences in feeding zones. Three albatrosses and a petrel feed mainly on squid and there are differences in both the species and size of the prey of each. The remaining seabirds chiefly take krill (although the giant petrels are extensive scavengers and some smaller petrels specialize on copepods) and utilize different feeding methods and areas to do so. Various adaptations related to inshore and offshore feeding zones are discussed. Although most species possess a combination of ecological isolating mechanisms additional evidence for the particular importance of dietary differences is presented.

Description: A small collection of otoliths was obtained from scatsof sub-adult male Antarctic fur seals Arctocephalus gazella at Bird Island, South Georgia. A reference collection of otoliths from South Georgia fish was used to identify the material and to derive relationships between otolith length and fish weight which were then applied to the sample otolith, after correcting for loss of material during digestion. The pelagic icefish Chamsocephalus gunnari was the main prey, in terms of numbers (55%) and weight (76%) of fish consumed. Other species taken include thelantern fish Gymnoscoscopelus nicholsi, the nototheniids Notothenia rossii. Notothenia gibberifrons, and Patagonotothen larseni and Pseudochaenichthys georgianus. The estimated mean weight of the C. gunnari specimens was 160kg (range 45-560g) and most were young adults aged 3-5 years; individuals of other species were mainly much smaller.

Description: A check list od South Georgia birds in presented, giving details of all new records from 31 January 1977 to 30 April 1982 an summarizingrevised information on the status of many of the breeding species. In this period, 22 visiting or vagrant species have been recorded, seven for the first time at South Georgia, including the first species of Palaecrctic origin, little stint an European house martin, and substantial numbers of cattle egrets. One new breeding species, fairy prion, was discovered. The total avifauna now consists of 30 breeding species an 36 visitors and vagrants.

Description: The habitals utilized by burrowing petrels at Bird lsland, South Gcorgia are described and the habitat modifications induced by the activities of fur seals and other seabirds summarised. The field methods for an investigation of the distribution and abundance of the nine species of burrow-dwelling petrels that breed on Bird lsland are described in detail. About 40% of the 200 hectares of ground suitable for burrow excavation was investigated using a system of grid squares each 3600 m² in area. ln each square, two randomly located circular quadrats of area 36 m² were studied. For each quadrat, aspect, slope, vegetation types and their cover, extent of fur seal influence and status of every burrow were recorded. Seven categories of both empty and occupied burrows were recognized and examination techniques (including use of tape-recorded calls to facilitate species identification) are described in detail. Over 5000 burrows were examined, with dove prion the most abundant species.

Description: Published information appears to be lacking on the chemical composition and calorific content of Southern Ocean squid, which are important prey of sperm whales and many seabirds. Data for 17 species of squid (all but one from the Northern Hemisphere) are reviewed. lt is concluded that they have calorific contents distinctly lower than those of Antarctic fish and krill, mainly because of lower Iipid content. Because of the importance of such information to studies of energy transfer between trophic Ievels, it is recommended that data on the chemical composition and calorific content of Antarctic squid should be rapidly obtained.

Description: Regurgitations of the chicks of wandering albatrosses near their nests included 762 upper beaks (mandibles) and 532 lower beaks of cephalopods. Twenty-five species of cephalopod are present in the diet. Analysis of the complete samples shows the three most important species in the diet to be Kondakovia longimana (40.0% by number), Taonius pavo (16.9%) and Histioteuthis(?) eltaninae (8.7%). While the large Taningia danae only comprises 1.3% by number, it may contribute over 5% by weight. The species and size ranges of beaks are compared with those occurring in the stomachs of sperm whales killed by whalers in the Southern Hemisphere (Clarke, 1980). The ten complete samples contain an average of 44 beaks which probably represents about 200 days' accumulation. Both Antarctic and warm-water cephalopods are present in the diet. These albatrosses possibly scavenge some of thei food from vomit of sperm whales.

Description: King Penguins are the second largest of all diving birds and share with their congener, Emperor Penguins, breeding habits strikingly different from other penguins. Our purpose was to determine the feeding behavior, energetics of foraging and the prey species, and compare these to other sympatric species of subantarctic divers. We determined: (1) general features of foraging behavior using time—depth recorders, velocity meters, and radio transmitters, (2) energetics by doubly labeled water, (3) food habits and energy content from stomach lavage samples, and (4) resting and swimming metabolic rate by oxygen consumption measurements. The average foraging cycle was ≈6 d, during which the mass gain of 30 birds was ≈2 kg. When at sea, the birds exhibit a marked pattern of shallow dives during the night, whereas deep dives of 〉100 m only occurred during the day. Maximum depth measured from 34 birds and 18 537 dives was 304 m, and maximum dive duration from 23 birds and 11 874 dives was 7.7 min. The frequency distribution of dive depth was bimodal, with few dives between 40 and 100 m. Overall, swim velocities when a bird was at sea averaged 2.1 m/s (N = 5), while descent and ascent rates of change in depth averaged 0.6 m/s for dives 〈60 m (N = 74) and 1.4 m/s for dives 〉150 m (N = 90). Night feeding dives occurred at a rate of ≈20 dives/h, and deep dives occurred at a rate of ≈5 dives/h. The energy consumption rate while resting ashore was 3.3 W/kg (N = 3) or 1.6 times the predicted standard metabolic rate (SMR). The average energy consumption rate while away from the colony was 10 W/kg (N = 8) or 4.6 x SMR, compared to 4.3 x SMR estimated from a time—energy budget. The latter value is based on an average metabolic rate of 4.2 W/kg for three birds while resting in 5°C water and 9.6 W/kg while swimming at 2 m/s, which was extrapolated from the average of three birds swimming at 1 m/s. The average energy intake based on 9 stomach content samples was nearly 24.6 kJ/g dry mass. The main prey by number are myctophid fish of the species Krefftichthys anderssoni and Electrona carlsbergi. It was concluded that: (1) feeding begins ≈28 km from the colony, (2) prey is pursued night and day through its vertical movements, (3) vertical distribution of the prey is reflected closely by diving habits of the birds, (4) deep—diving, for unknown reasons, is an important component of foraging success, (5) diving capacities of King Penguins are remarkable compared to other birds and many pinnipeds, and (6) calculated foraging energetics can be closely estimated from time—energy budgets.

Description: To investigate the role of sea ice cover on penguin populations we used principal component analysis to compare population variables of Adélie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguins breeding on Signy Island, South Orkney Islands with local (from direct observations) and regional (from remote sensing data) sea ice variables. Throughout the study period, the Adélie penguin population size remained stable, whereas that of chinstrap penguins decreased slightly. For neither species were there significant relationships between population size and breeding success, except for an apparent inverse density-dependent relationship between the number of Adélie breeding pairs and the number of eggs hatching. For both species, no general relationship was found between either population size or breeding success and the local sea ice conditions. However, the regional sea ice extent at a particular time prior to the start of the breeding season was related to the number of birds that arrived to breed. For both species, this period occurred before the sea ice reached its maximum extent and was slightly earlier for Adélie than for chinstrap penguins. These results suggest that sea ice conditions outside the breeding season may play an important role in penguin population processes.

Description: Adélie (Pygoscelis adeliae) and chinstrap penguins (P. antarctica) are morphologically and ecologically very similar, have very similar diet and breed sympatrically in the Scotia Arc from the South Sandwich Islands to the Antarctic Peninsula. To investigate how these two species co-exist, their foraging distribution and diet were studied during the chick-rearing period at Signy Island, South Orkney Islands, during the breeding seasons of 2000 and 2001. Satellite tracking data from of 19 Adélie penguins and 24 chinstrap penguins were used to compare foraging distributions. In both years the diet of both species was exclusively Antarctic krill (Euphausia superba) of the same size range. In a year of low prey availability (2000), there was a statistically significant segregation of foraging areas between the two species, however, in a year of normal resource availability (2001) there was no such segregation. There was a significant difference in the foraging areas used by Adélie penguins between years but not for chinstrap penguins. Adélie penguins foraged significantly farther (mean 100 km) from the colony than chinstrap penguins (mean 58 km) in 2000 but not in 2001 (mean 58 km and 35 km respectively). In 2000, the breeding success of Adélie penguins was 51% lower than the long-term mean compared to 15% lower in chinstrap penguins. Both species achieved above average breeding success in 2001. The changes in foraging distribution and breeding success suggest that in years of low resource availability, chinstrap penguins may be able to competitively exclude Adélie penguins from potential inshore foraging areas. Current trends in climatic change and possible effects on ice distribution and krill abundance suggest that conditions could become less favourable for Adélie penguins than chinstrap penguins in areas where both species occur.