THE BREEDING BIOLOGY AND DISTRIBUTION OF ADELlE PENGUINS: ADAPfATIONS TO ENVIRONMENTAL VARIABILITY

Adtlie penguins are long-lived, highly philopatric seabinls Iilat dominate the bird biomass of the Western Antarctic Peninsula region, and serve as focal animals for our Long·Tenn Ecological Research (LTER) study of the effects of environmental variability on animal populations in the Antarctic marine ecosystem. The major pbysica1 factors affecting the breeding success, distribution and demography of Adl!lie penguins in the Southern Ocean are variability in sea ice cover, ocean circulation patterns and terrestrial topography_ We analyzed Ad~tie distributions in the Antarctic Peninsula region and concluded that Ad~lie penguins have discrete subpopulations in the nonheaslem and southwestern regions of the area. These 5ubpopulations are separated by a 400 kIn gap in their respective distributions, but each is within several hundred kilometers of predictable pack ice areas in the Weddell and Bellingshausen Seas, respectively. We propose that these pack ice areas are the wintering grounds for each subJXlPUlation, and that access to these pack ice areas, early in the season following courtship fasting. is the key to successful breeding in A~lies. We further analyzed the colony distributions within each subpopulation and found highly clumped distributions of Adelie pen· guins that were strongly correlated to physicaJ factors such as bathymetry, CUJTt:nts and wind direction. We propose that these variables reduce the occurrence of pack ice in the vicinity of breeding colonies of Ad~lie penguin populations, thereby assuring access to open water in the early season. Finally, we examined the influence of the interaction of loca1 topography and weather on the size. location and persistence of breeding groups within A~lie penguin colonies. Snow accumulation, melt water runoff and solar radiation all impact the microclimate of breeding colonies and influence the selection of nesting sites among Ad~lie penguins. The abandonment of breeding areas by Ad~lie penguins, following two to three years of failure at "poor" sites. suggests that changes in the population distribution of Ad~lie penguins may be very rapid in response to changing environmental conditions, such as increased snow deposition. Adaptations to environmental variability are seen in every aspect of the natural history of the Ad~lie penguin, from the distribution of subpopulations around Antarctica, to the sizes and distributions of colonies within regions, to the choice of breeding sites within colonies.