Arctic ground squirrel hibernation trend could affect mating

An arctic ground squirrel raises its head above snow.
Photo by Øivind Tøien
An arctic ground squirrel peers over snow. A recent study conducted using data collected exclusively from the Institute of Arctic Biology’s Toolik Field Station has revealed that female arctic ground squirrels are ending their hibernation cycle early and emerging from hibernation on average 10 days earlier than they did 25 years ago.

As soils in Arctic Alaska become warmer and freeze for shorter periods in winter, mating conditions for arctic ground squirrels are changing. 
New research published in the journal Science analyzes more than 25 years of climate and biological data gathered by researchers and students from the Institute of Arctic Biology at the University of Alaska Fairbanks. The team members found that hibernating ground squirrels are delaying the dates when they begin to regulate their body temperature to survive the frigid winter. They also found that female ground squirrels are ending their hibernation periods earlier.

Over decades, the data indicate that, on average, females now become active above ground in spring 10 days earlier than they did a quarter century ago. The changes in females match earlier spring warming of the soil.

This earlier end to female hibernation periods could create both positive and negative ripple effects throughout the food web in Arctic ecosystems.   

Squirrels that emerge earlier don’t need to use as much stored fat during hibernation and can begin eating sooner, potentially resulting in healthier females. Mating also could be more successful at present because the females’ recent earlier awakening might better match that of males, which have tended to wake up before females but to remain underground longer. Litters may also survive better.
On other hand, earlier emerging females will face increased threats from predators like foxes, wolves, bears and golden eagles. And if females’ hibernation periods continue to shrink, it could mean a future mismatch during mating cycles between them and their would-be male suitors. 

Senior author Cory Williams, an assistant professor with Colorado State University, began studying arctic ground squirrels while at IAB more than 15 years ago.
“I think the thing that makes our study unique is that we are looking at a long-enough data set to show the impacts of climate change on a mammal in the Arctic,” Williams said in a news release for CSU.

Williams, who was previously a postdoctoral researcher and assistant professor at IAB, is one of several former UAF faculty, undergraduate and graduate students involved in the study, and is one of the two co-authors on the paper. The fieldwork took place out of IAB’s Toolik Field Station, located in the northern foothills of the Brooks Range 370 miles north of Fairbanks.

Lead author Helen Chmura, currently a U.S. Forest Service researcher with the Rocky Mountain Research Station, began her work on this project as a postdoctoral fellow at IAB in 2018.
“Our data show that the active layer, the soil layer above the permafrost, freezes later in the fall and begins to thaw earlier in the spring, and it’s not getting as cold in the middle of winter,” Chmura said in a news release for the Rocky Mountain Research Station. 

Brian Barnes, professor with IAB and also a co- author of the paper, originally discovered in the late 1980s that arctic ground squirrels are capable of supercooling their bodies to temperatures as low as minus 3 degrees Celsius or 27 degrees Fahrenheit.  
“This study is certainly remarkable for its long-term nature, but it’s also an example of how students at UAF were able to dig deep into big data associated with biology and soils pertaining to arctic ground squirrels,” Barnes said. “The ability of students to contribute to novel research such as this long-term data set is indicative of the unique Arctic-focused research opportunities at UAF.”
Arctic ground squirrels survive harsh Alaska winters by hibernating for over half the year, drastically slowing their lungs, heart, brain and body functions. Still, when the ground surrounding their underground nests falls well below freezing, they must continuously spend energy to generate enough heat to keep themselves alive. The fall onset of hibernation is becoming later and later, allowing squirrels to emerge in spring in better condition. 
The research team members analyzed data for the long-term air and soil temperatures from two sites near Toolik Lake. They compared that information to data from  biologgers that measured abdominal and-or skin temperature of 199 free-living individual ground squirrels in the same locations over the same 25-year period. The biologger data reflect the hibernation behavior of the ground squirrels on almost an hourly basis. 

Barnes thinks the mere fact that such a long-term data set exists is a worthy accomplishment. When he first began researching the arctic ground squirrel, he was not assured that his work would sustain a 25-year legacy, spawning awe-inspiring data sets and shaping his career trajectory and those of his students.

Beginning field scientists should consider such possibilities, he said.

“Always consider in the approach and design of your initial study how it might hold up over a lifetime,” he said. “Our initial fieldwork, which focused on individual squirrels and their survival strategies, has had unanticipated and far-reaching benefits for observing long-term interactions of climate and animal populations.”

ADDITIONAL CONTACT: Brian Barnes,  Institute of Arctic Biology professor,, 907-474-7649.