I used 8 years of mark-recapture data to test alternative hypotheses about the relative influence of winter climate, social structure, and life history on survival, reproduction, and population dynamics of hoary marmots (Marmota caligata) in the southwest Yukon. Climate, characterized by the mean winter Pacific Decadal Oscillation index (PDO), was strongly related to juvenile survival, more weakly linked with adult survival and fecundity, and did not appear to influence breeding probability. Group social structure had little influence on population dynamics. Variation in adult and juvenile survival affected the population growth rate more strongly than fecundity or breeding probability, but the relative influence of life history parameters changed from year to year. Comparisons between hoary marmots and other alpine mammals indicated that the average environment to which an animal is adapted, the strategies employed to survive winter, and life history constraints may all affect demographic sensitivity to winter climate.