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Pygoscelid penguin populations throughout the Antarctic Peninsula region have changed rapidly in recent decades. Ongoing climate change is thought to underpin these changes through bottom-up effects on habitat suitability and prey availability, ultimately affecting penguin behavior, survival and reproduction. To quantify winter behavior and energetic requirements required to support winter activity and to estimate population-level consequences of variation in survival rates under conditions of rapid climate change, this dissertation investigates two projects, each using a different penguin species. Daily activity and energetic demands during winter were estimated for gentoo penguins (Pygoscelis papua) using data from archival temperature tags. Foraging trip frequencies ranged from 0.85 to 1.0 trips day⁻¹ and total trip durations were positively correlated with day length. Mean daily food requirements, based on a mixed diet of fish and krill (Euphausia superba) were estimated at 0.70 ± 0.12 kg day⁻¹. Early winter foraging trips matched day length better than late winter foraging trips, suggesting that individuals maximized foraging time during the early winter period to recover body mass following the breeding season and molt. The attenuated response of foraging trip durations to increasing day length in late winter may be related to differences in local resource availability or individual behaviors prior to the upcoming breeding season. To investigate population-level consequences of variation in survival rates, data from long-term mark-recapture studies of Adélie penguins (Pygoscelis adeliae) were integrated in a stochastic population model to estimate the risk of local extirpation. No trends in survival rates were evident, and variability in survival rates was poorly explained by the selected suite of environmental covariates. Stochastic projections based on the extant variability of survival rates suggests that small increases in the frequency of years with poor survival result in a rapid increase in risk of near-term local extirpation. Compared to other populations of Adélie penguins around the Antarctic continent, survivorship and population growth rates were lowest in the northern Antarctic Peninsula region. Despite no simple correlations with environmental indices, it is readily apparent that Adélie penguins are vulnerable to the rapid environmental changes that are occurring in the Antarctic Peninsula region