Arctic ground squirrel hibernation trend could affect mating
Amy Loeffler
907-474-7933
June 1, 2023
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 ķƵ. 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, bmbarnes@alaska.edu, 907-474-7649.
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