AGS Parturition DatesArctic ground squirrel parturition dates as determined by body temperature.Parturition_Dates.csvAGS Female Spring Arousal DatesDates female arctic ground squirrels returned to euthermia each springFemale_Spring_Arousal_Dates.csvAGS Male Spring Arousal DatesDates male arctic ground squirrels first became euthermic each springMale_Spring_Arousal_Dates.csv2010_Tb_filesZIP file containing body temperature data for arctic ground squirrels during the 2009-10 hibernation season. The ID in the file name is based on the eartag at the time of download - this can be matched to the unique ID from the parturtion date or arousal date files (eartag # can change across years).2011_Tb_filesZIP file containing body temperature data for arctic ground squirrels during the 2010-11 hibernation season. The ID in the file name is based on the eartag at the time of download - this can be matched to the unique ID from the parturtion date or arousal date files (eartag # can change across years).2012_Tb_FilesZIP file containing body temperature data for arctic ground squirrels during the 2011-12 hibernation season. The ID in the file name is based on the eartag at the time of download - this can be matched to the unique ID from the parturtion date or arousal date files (eartag # can change across years).2013_Tb_FilesZIP file containing body temperature data for arctic ground squirrels during the 2012-13 hibernation season. The ID in the file name is based on the eartag at the time of download - this can be matched to the unique ID from the parturtion date or arousal date files (eartag # can change across years).2014_Tb_FilesZIP file containing body temperature data for arctic ground squirrels during the 2013-14 hibernation season. The ID in the file name is based on the eartag at the time of download - this can be matched to the unique ID from the parturtion date or arousal date files (eartag # can change across years).2015_Tb_FilesZIP file containing body temperature data for arctic ground squirrels during the 2014-15 hibernation season. The ID in the file name is based on the eartag at the time of download - this can be matched to the unique ID from the parturtion date or arousal date files (eartag # can change across years). Site data is found in the parturition and arousal data files.

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.