Nonlinear effects of winter sea ice on the survival probabilities of Adelie penguins

The population dynamics of Antarctic seabirds are influenced by variations in winter sea ice extent and persistente; however, the type of relationship differs according tu the region and the demographic parameter considered. We used annua1 presencelabsence data obtained from 1,138 individually marked hirds to study the influence of environmental and individua1 characteristics on the survival of Adélie penguins Pyfioscelis rideline at Edmonson Point (Ross Sea, Anrarctica) between 1994 and 2005. About 25% of 600 birds marked as chicks were reobserved at the natal colony. The capture and survival rates of Adélie penguins at this colony increased with the age of individuals, and five age classes were identilied for both parameters. Mean adult survival was 0.85 (SE = 0.01). and no effect of sex on survival was evideiit. Breeding propensity, as measured by adult capture rates, was dose to one. indicating a constant breeding effort through time. Temporal variations in survival were best explained by a qiiadratic relationship with winter sea ice extent anomalies in the Ross Sea, suggesting that for this region optiinal conditions are intermediate between too much and too little winter sea ice. This is likely the result of a balance between suitable wintering habitat and food availability. Survival rates were not correlated with the Southem Oscillation Index. Low adult survival after a season characterized by severe environmental conditions at breeding hut favorable conditions during winter suggested an additional mortality inediated by the reproductive effort. Adélie penguins are sensitive indicators of environmental changes in the Antarctic, and the results from this study provide iiisights iiito regional responses of this species to variability in winter sea ice habitat