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The most commonly reported ecological effects of climate change are shifts in phenologies, in particular of warmer spring temperatures leading to earlier timing of key events. Among animals, however, these reports have been heavily biased towards avian phenologies, while we still know comparatively little about other seasonal adaptations such as mammalian hibernation. Here we show a significant delay (0.47 days per year over a 20 year period) in hibernation emergence date of adult females in a wild population of Columbian ground squirrels in Alberta, Canada. This finding was related to the climatic conditions at our study location: due to within-individual phenotypic plasticity, females emerged later during years of lower spring temperature and delayed snowmelt. Although there has not been a significant annual trend in spring temperature, the date of snowmelt has become progressively later due to an increasing prevalence of late season snowstorms. Importantly, years of later emergence were also associated with decreased individual fitness. There has consequently been a decline in mean fitness (i.e., population growth rate) across the last two decades. Our results illustrate that plastic responses to climate change may: (i) be driven by climatic trends in addition to warming temperature; and (ii) be associated with declines in individual fitness and, hence, population viability.
- Climate science