Geographic Structure of Adelie Penguin Populations: Demography of Population Expansion

H.T. Harvey & Associates, Los Gatos CA

Investigators

Abstract

Adelie penguin (Pygoscelis adeliae) populations in the Ross Sea region, Antarctica have been undergoing change in recent times. Changes in environmental conditions have also been noted, particularly changes in the sea ice condition, an important variable related to foraging ecology of these seabirds. The focus of this renewal project is to investigate the mechanisms responsible for geographic structuring, the founding of new colonies, and recent population expansion of Adelie penguins. Past research has shown that none of the colonies is nesting-space limited, and that sea-ice extent and concentration affect diet, foraging effort (and ultimately chick growth and survival), and over-winter survival. In addition, large colonies affect the foraging patterns of smaller ones within foraging range and, perhaps ultimately, the size of those colonies. While quantification of emigration is still in progress, its rate and direction appear also to be constrained by sea ice conditions, with reasonable concentrations of ice favoring growth of smaller colonies, where foraging competition is minimal. The current research will address the demographic mechanism of colony growth (or decline), including changes in adult survival, juvenile survival, recruitment age, proportion of adults breeding, emigration/immigration, or a combination of these factors. Research will include census work at three colonies on the Ross Sea coast: Cape Crozier, Cape Royds and Cape Bird as well as Beaufort Island. The four colonies differ in size and demography. The work will involve continuing a seven-year census record and includes known-age birds. The research team will use such technology as: computerized weighbridges that assess foraging effort and success, as well as quantify such difficult problems as band loss; time-depth-recorders and satellite transmitters to assess foraging behavior with respect to sea ice and overlap among colonies; and archival tags that, using celestial cues (time of sunset and sunrise, day length), determine migration timing and routes, and location of molting and wintering areas. Information will be related to sea-ice conditions as quantified by satellite images. Results will increase an understanding of population regulation and patterns of dispersion and the effects of climate change, mediated through changes in sea ice condition on populations.