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Demographic parameters were estimated for snow petrels Pagodroma nivea nesting at the study colony of Reeve Hill near Casey station, Antarctica between 1984 and 2003. Average breeding success for the colony varied from 18.2% to 76.5%. Breeding effort, hatching and fledging success were subject to a high interannual variability. We examined the influence of regional sea-ice extent on the breeding performance of snow petrels at Reeve Hill. Fewer birds were breeding when sea-ice had been extensive during April-May. Overall breeding success and fledging success were improved during years with extensive sea-ice cover in winter. Successful breeding effort and breeding success were depressed when there was extensive sea-ice cover during January-February. Sea surface temperatures also correlated to snow petrel breeding performance parameters. Previous work showed that large-scale climatic events (ENSO, Antarctic circumpolar wave) and the related sea-ice cover around the Antarctic might affect the lower trophic levels of the marine environment and consequently food availability for snow petrels. A comparison with the long-term study conducted at Ile des Pe´trels (Terre Ade´lie) suggests that despite similarities in the underlying biological processes that control snow petrel breeding performance, the nature of the correlation of large-scale environmental factors with breeding performance differs substantially between the two colonies, probably because of the confounding effects of other environmental factors acting at a local scale (local weather, nest quality), which also affect bird body condition.

We studied lactation behaviour in relation to pup growth in southern elephant seals (Mirounga leonina) at Macquarie Island, and compared harems in areas of high and low human presence to determine if there is an effect attributable to human activities, including scientific research. Pup weaning mass, a known correlate of first-year survival, was positively influenced by suckle bout durations during early and middle lactation and by maternal aggression during late lactation; no other behavioural variables were associated with weaning mass. In the area of high human presence, we observed from a distance the behaviour of mother-pup pairs directly before, during, and after visits to harems by other researchers. Alertness was raised threefold in the presence of people but quickly returned to predisturbance levels after their departure; there were no significant short-term effects on other behavioural variables. In the areas of high and low human presence, we observed the undisturbed behaviour of the seals in the absence of other people. No significant differences in any behavioural variables examined were found, indicating no long-term changes in behaviour resulting from human presence. Human disturbance therefore appears not to have significantly contributed to the population decline observed at Macquarie Island, but the conclusion requires caution given the fairly low power of our analyses

Antarctic petrels Thalassoica antarctica on Ardery Island, Antarctica (66°S, 110°E), experienced major reductions in breeding success and breeder survival over four seasons between 1984/85 and 1996/97. In 1996 the reason was revealed. A large snowdrift covered part of the study colony on the cliffs. Southern giant petrels Macronectes giganteus, normally lacking access to this area, exploited the snow for soft ‘crash landings”. After landing they waited for the disturbed birds to resettle on their nests and then used surprise to seize and kill a victim. Predation continued into the egg period, and only stopped after the snowdrift had melted. Giant petrels showed no interest in the eggs but, during the panic caused by their activities, South Polar skuas Catharacta maccormicki took the deserted eggs. Antarctic petrel mortality due to predation within the 1996/97 season amounted to 15.4% of experienced breeders, and breeding success was reduced to virtually zero. Weather data from the nearby Casey station over the 1980–96 period showed that a significant increase in precipitation has occurred, in combination with shifts in speed and direction of winds. We conclude that the decreases in breeding success and survival in earlier seasons were also related to increased snowfall and predation. Although similar predation behaviour by giant petrels has not been reported before, we think that it is long established and explains why nesting of the smaller fulmarine petrels is limited to steeper cliffs or sheltered sites. The complexity of the response seems unlikely to be predicted by our present understanding of how climate change affects ecosystems.

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