As Arctic warms, female arctic ground squirrels end hibernation before males – a mismatch with consequences

As Alaskan permafrost warms, hibernating arctic ground squirrels generate less heat, causing females to emerge from hibernation up to 10 days before their male counterparts – a mismatch that could have large, cascading ecological impacts. The findings of the related study reveal both direct and indirect impacts of a warming world. Winter temperatures play a fundamental role in fitness and population dynamics for many species that live in higher latitudes. However, in the Arctic, where warming is occurring more rapidly than most other places on Earth, rising winter temperatures are altering the phenology, or timing, of key seasonal animal behaviors, like migrations or hibernation. However, despite the rapid rate of Arctic climate warming, few long-term studies merge physical records of climate change and physiological responses of Arctic species. To evaluate the physiological impact of recent climate change on arctic ground squirrels (Urocitellus parryii), Helen Chmura and colleagues combined long-term air and soil temperature records at two sites in Arctic Alaska with a 25-year hibernation record for this species. They found that, over the past several decades, winter freezing of permafrost has slowed, resulting in a shift in the timing and duration of when squirrels up-regulate body heat generation during hibernation. What’s more, Chmura et al. discovered sex differences in phenological responses to this warming – female squirrels have increasingly emerged from hibernation earlier, advancing their spring active season by 10 days over the last 25 years, with males showing no such change over time. The authors argue that this phenological mismatch could potentially have a variety of repercussions for arctic ground squirrel population dynamics and the functioning of Arctic food webs. While reduced thermogenesis due to warming temperatures could allow the squirrels to conserve energy and, thus, increase winter survival, a shortened hibernation season could also increase the exposure of the animals to hungry predators, altering mortality rates, particularly for earlier emerging female squirrels. The phenological mismatch between the sexes may also disrupt reproductive rates. And over longer time scales, continued warming in the Arctic may lead to changes in male squirrel seasonal behaviors, say the authors.