Wintering behavior of Arctic ground squirrels

Among mammals, Arctic ground squirrels are unique. Their ability to avoid freezing even when their body temperatures drop below that level on the thermometer makes it easier for them to withstand harsh winter climates. A novel study was reported in Science. Examines more than a quarter of a century of biological and climatic data.

A juvenile arctic ground squirrel foraging near the Toolik Field Station in northern Alaska. Image Credit: Cory Williams

Results include shorter hibernation durations and differences between male and female hibernation periods. Spoiler alert: Chicks “rise and shine” a bit early with respect to warming, which could have a positive or negative ripple effect throughout the food web in such ecosystems.

Cory Williams, lead author and assistant professor in the Department of Biology at Colorado State University, began examining Arctic ground squirrels when he was at the University of Alaska Fairbanks more than 15 years ago.

I think what makes our study unique is that we’re looking at a data set long enough to show the impacts of climate change on a mammal in the Arctic. We can show a direct link between temperature changes and the physiology and ecology of these animals..

Cory Williams, lead author and assistant professor, Department of Biology, Colorado State University

The lead author of this new study, Helen Chmura, began the research while she was a postdoctoral fellow at the University of Alaska Fairbanks in 2018. She now works as a USDA Forest Service investigator at the Rocky Mountain Research Station.

Our data shows that the active layer, the layer of soil above the permafrost, freezes later in the fall, does not get as cold in the dead of winter, and thaws slightly earlier in the spring. These changes, which are equivalent to a reduction of about 10 days in the time the ground freezes at a depth of one meter, have occurred in just 25 years, which is quite fast..

Helen Chmura, lead study author, Rocky Mountain Research Station

Arctic ground squirrels endure the harsh winters of Alaska by hibernating for more than six months of the year, which extremely slows down the functions of their heart, lungs, body, and brain. Still, they must use energy to produce enough heat from stored fat to prevent tissue from freezing. They reemerge from their burrows that are more than 3 feet below the ground each spring, hungry and eager to mate.

Soil and temperature data

Chmura and Williams, as well as co-authors, examined long-term air and ground temperature data at two sites in Arctic Alaska along with data collected using biologgers. They quantified the skin and/or abdominal temperatures of 199 individual free-living ground squirrels over the same 25-year period. They found that females undergo changes when they complete hibernation, emerging earlier each year compared to males.

The modifications in the females correspond to a previous spring thaw. The benefit of this is that they do not need to expend as much stored fat at the time of hibernation and can start foraging for shoots and roots, seeds and berries in early spring. The researchers believe this could result in higher survival rates and healthier litters.

The downside is that if males also do not alter hibernation patterns, ultimately there could be a mismatch in existing “date nights” for females and males. Additionally, ground squirrels are an essential food source for various predators including wolves, foxes, and eagles. Increased exposure and the threat of being eaten is an indirect consequence of being active above ground for longer.

No clear winners and losers

A big mystery is what will happen to the population: there are no obvious losers and winners. Although hibernation requires minimal energy, which could help them survive through the winter, ground squirrel numbers also depend on how predators react to weather disturbances. For now, Williams says, “Our article shows the importance of long-term data sets in understanding how ecosystems are responding to climate change..” Chmura approved, adding: “It takes a great team to continue a data set like this for 25 years, especially in the Arctic..”

Other contributing authors are Brian Barnes of the University of Alaska Fairbanks and Loren Buck of Northern Arizona University, who began this research in the 1990s to study how Arctic ground squirrels endure such long, dark, and winters. cold and just how cold their hibernation places were. .

These questions encouraged them to install the first soil temperature monitors, and as technology advanced, they were able to quantify those temperatures throughout the winter. Cassandra Duncan and Grace Burrell helped with the study while studying at the University of Alaska Fairbanks.

Magazine reference:

Chemura, H. and others. (2023) Climate change is altering the physiology and phenology of an arctic hibernator. Science.