Hibernation provides a means of escaping the metabolic challenges associated with seasonality, yet the ability of mammals to prolong or re-enter seasonal dormancy in response to extreme weather events is unclear. Here, we show that arctic ground squirrels in northern Alaska exhibited sex-dependent plasticity in the physiology and phenology of hibernation in response to a series of late spring snowstorms in 2013 that resulted in the latest snow-melt on record. Females and non-reproductive males responded to the >1 month delay in snow-melt by extending heterothermy or re-entering hibernation after several days of euthermy, leading to a >2-week delay in reproduction compared to surrounding years. In contrast, reproductive males neither extended nor re-entered hibernation, likely because seasonal gonadal growth and development and subsequent testosterone release prevents a return to torpor. Our findings reveal intriguing differences in responses of males and females to climatic stressors which can generate a phenological mismatch between the sexes.