DYNAMICS OF ANTARCTIC PENGUIN POPULATIONS IN RELATION TO INTERANNUAL VARIABILITY IN SEA-ICE DISTRIBUTION

To investigate the role of sea ice cover on penguin populations we use d principal component analysis to compare population variables of Adel ie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguins breeding on Signy Island, South Orkney Islands with local (from direc t observations) and regional (from remote sensing data) sea ice variab les. Throughout the study period, the Adelie penguin population size r emained stable, whereas that of chinstrap penguins decreased slightly. For neither species were there significant relationships between popu lation size and breeding success, except for an apparent inverse densi ty-dependent relationship between the number of Adelie breeding pairs and the number of eggs hatching. For both species, no general relation ship 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 relate d 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 Adelie than for chinstrap penguins. These result s suggest that sea ice conditions outside the breeding season may play an important role in penguin population processes.