Climate change affects arctic ground squirrel hibernation

Arctic ground squirrels possess a remarkable ability that sets them apart from other mammals. Despite facing freezing temperatures, they can avoid freezing themselves, allowing them to survive in extremely harsh winter climates. A recent study published in Science examines over 25 years of climate and biological data to shed light on the behavior of these squirrels during hibernation. The research reveals interesting findings, such as shortened hibernation periods and variations between male and female squirrels. Surprisingly, female squirrels awaken earlier in response to warming temperatures, which could have both positive and negative consequences throughout the ecosystem.

Cory Williams, an assistant professor in the Department of Biology at Colorado State University and the senior author of the study, has been studying arctic ground squirrels for over 15 years, initially at the University of Alaska Fairbanks. According to Williams, what sets their study apart is the extensive dataset they have collected, which allows them to demonstrate the direct impact of climate change on Arctic mammals. Williams explains that they can establish a clear connection between temperature changes and the physiological and ecological responses of these animals.

The lead author of the study, Helen Chmura, initiated the analysis during her time as a postdoctoral fellow at the University of Alaska Fairbanks in 2018. Currently, she works as a researcher with the USDA Forest Service at the Rocky Mountain Research Station. Chmura emphasizes that their data reveals significant changes in the Arctic environment. The active layer, which is the layer of soil above the permafrost, now freezes later in the autumn, experiences milder winter temperatures, and thaws slightly earlier in the spring. These alterations, which amount to approximately a 10-day reduction in the duration of frozen soil at a depth of one meter, have occurred within just 25 years—a relatively rapid timeframe.

A juvenile arctic ground squirrel foraging near Toolik Field Station in northern Alaska. Credit: Cory Williams/Colorado State University

Arctic ground squirrels have developed a unique survival strategy to endure the harsh winters of Alaska. They enter a deep hibernation state for more than half the year, drastically slowing down their bodily functions, including their lungs, heart, brain, and overall metabolism. However, even during hibernation, they need to expend energy to generate enough heat from their stored fat to prevent their tissues from freezing. When spring arrives, these squirrels resurface from their burrows, which can be more than three feet deep underground, in a state of extreme hunger and readiness to mate.

To gain insight into the behavior of these squirrels, Chmura, Williams, and their co-authors conducted an extensive analysis. They studied long-term air and soil temperature data from two locations in Arctic Alaska and used biologgers to measure the abdominal and/or skin temperature of 199 individual ground squirrels over a span of 25 years. Their findings revealed an interesting trend: female squirrels are adjusting their hibernation patterns, consistently emerging earlier each year, while male squirrels are not exhibiting the same changes. The shift in female behavior aligns with the earlier onset of spring thaw.

This phenomenon has its advantages. By ending hibernation earlier, female squirrels can minimize the amount of stored fat they need to utilize during hibernation and start foraging for food sources like roots, shoots, berries, and seeds earlier in the spring. This, in turn, could potentially lead to healthier litters and increased survival rates for the species.

However, there is a potential downside to this mismatch in hibernation patterns between males and females. If the males do not adjust their hibernation timing accordingly, it could result in a lack of available mating opportunities, disrupting the breeding cycle. Additionally, being active above ground for longer periods increases the squirrels’ exposure and vulnerability to predators. Ground squirrels play a crucial role in the food chain, serving as a vital food source for predators like foxes, wolves, and eagles. Therefore, the extended above-ground activity carries a higher risk of predation for the squirrels.

A juvenile arctic ground squirrel foraging near Toolik Field Station in northern Alaska. Credit: Cory Williams/Colorado State University
A juvenile arctic ground squirrel foraging near Toolik Field Station in northern Alaska. Credit: Cory Williams/Colorado State University

The future of the Arctic ground squirrel population remains uncertain, with no clear winners or losers. While hibernation offers the advantage of reduced energy expenditure, which could enhance survival during the winter, the population dynamics of ground squirrels are also influenced by the response of predators to climate changes. As of now, the study’s senior author, Williams, emphasizes the significance of long-term datasets in comprehending the ecological responses to climate change. Chmura concurs, highlighting the challenging task of maintaining a dataset spanning 25 years, particularly in the Arctic region.

Two other researchers, Brian Barnes from the University of Alaska Fairbanks and Loren Buck from Northern Arizona University, have been pivotal contributors to this study since the 1990s. Their primary objective was to gain insights into how Arctic ground squirrels endure the long, cold, and dark winters, as well as to determine the temperatures experienced in their hibernation burrows. This led them to install the initial soil temperature monitors, and with advancing technology, they were able to continuously measure these temperatures throughout the winter season.

Source: Colorado State University

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