Arctic ground squirrels have changed their hibernation patterns due to climate change

The Arctic ground squirrels, unique among their mammalian kin, have captured the curiosity of scientists for their incredible survival skill. They don’t freeze to death even when their body temperatures plummet below zero. This ability keeps them alive in some of the most inhospitable winter climates on the planet.

In a study published in the journal Science, an in-depth analysis spanning over a quarter of a century has shed light on how these creatures react to changing temperatures. 

Arctic ground squirrels are adapting, but not in a good way

Their hibernation periods, it turns out, are getting shorter, and intriguingly, differ between the sexes. The females, in a surprising twist, wake up from their winter slumber slightly ahead of the males.

This seemingly minor shift in wake-up calls may have profound impacts on the local ecosystems. These early risers, in turn, could set off a chain reaction affecting the entire food chain, with both positive and negative outcomes yet to be fully understood.

Cory Williams, a senior author of the study and an assistant professor at the Department of Biology at Colorado State University, brings more than 15 years of experience studying these squirrels. He began his research at the University of Alaska Fairbanks.

“The thing that makes our study unique is that we are looking at a long enough dataset to show the impacts of climate change on a mammal in the Arctic,” explained Professor Williams. He noted that this extensive research provides evidence of a direct link between changes in temperature and the physiology and ecology of these squirrels.

Helen Chmura, lead author of the study and a researcher at USDA Forest Service’s Rocky Mountain Research Station, began her analysis as a postdoctoral fellow in Alaska. “Our data show that the active layer, the soil layer above the permafrost, freezes later in the fall, doesn’t get as cold in the middle of winter, and thaws slightly earlier in the spring,” said Chmura.

She emphasized that these shifts, accounting for roughly a 10-day reduction in frozen soil, have happened over a mere 25 years – a rapid change in ecological terms.

How Arctic hibernation patterns have changed

Arctic ground squirrels hibernate for more than half the year to survive the brutal Alaska winters. During hibernation, they slow down their body functions to the bare minimum but still need to burn stored fat to prevent their tissues from freezing. Each spring, they emerge from burrows dug deep into the ground, starved and ready to mate.

In this extensive study, Chmura, Williams and their team used a range of biologging tools to measure the body temperatures of 199 free-living ground squirrels. They combined this data with long-term air and soil temperature data from two sites in Arctic Alaska. 

Interestingly, they found that only the female squirrels were adjusting their hibernation schedules and coming out earlier every year. Males appeared to stick to their old schedules.

The females’ shift to earlier spring emergence is in sync with the early thawing of spring. The positive side is that females can conserve their stored fat during hibernation and start foraging earlier in the spring. This could potentially lead to healthier offspring and increased survival rates.

However, if the males fail to adjust their hibernation patterns, it could result in fewer mating opportunities, disrupting the balance of the species. 

Importance of Arctic ground squirrels to the ecosystem

Ground squirrels are also an important food source for predators like foxes, wolves, and eagles. Longer periods above ground could lead to greater exposure and a higher risk of predation.

The consequences for the squirrel population remain uncertain – there are no clear winners or losers. Hibernation conserves energy, which might aid in winter survival. But predator responses to climate shifts could also impact ground squirrel numbers.

“Our paper shows the importance of long-term datasets in understanding how ecosystems are responding to climate change,” said Williams. 

Additional contributors to this research include Brian Barnes from the University of Alaska Fairbanks and Loren Buck from Northern Arizona University. Both began the study in the 1990s with the goal of understanding how Arctic ground squirrels could survive the extremely long, cold, and dark winters in the Arctic and exactly how cold their hibernation spots were.

New technology provided great results to the researchers

The initial curiosity around the squirrels’ survival strategies prompted them to install the first soil temperature monitors. As technology evolved over the years, they were able to continuously measure the soil temperature during winter. Cassandra Duncan and Grace Burrell, students at the University of Alaska Fairbanks, were also part of the research team.

This research marks a significant contribution to our understanding of the Arctic’s unique wildlife and the rippling effects of climate change. It is through this type of long-term, dedicated study that we can start to comprehend the profound impacts of changing temperatures on the delicate balances within Arctic ecosystems.

This analysis of the Arctic ground squirrels’ changing hibernation patterns reminds us of the resilience of nature, while simultaneously underscoring the vital importance of continued climate research. As ecosystems continue to adapt to a warming world, the full scope of these changes is yet to be discovered.

More about Arctic ground squirrels

Arctic ground squirrels (Urocitellus parryii) are remarkable creatures that are equipped with a variety of adaptations to help them survive in some of the world’s harshest climates. Here are some key facts and traits of Arctic ground squirrels:

Distribution and Habitat

These ground squirrels are native to the Arctic and are found across the northernmost parts of North America. They live in various regions, including Alaska, Northern Canada, and Siberia. They prefer open habitats like meadows, fields, or tundra.

Physical Features

Arctic ground squirrels are the largest among North American ground squirrels. They have a sturdy build and are generally brown or reddish-brown in color, with some white spotting.

Hibernation

Arctic ground squirrels are known for their extended hibernation periods, which can last for up to 8 months in a year. During hibernation, their body temperature can drop to below freezing, a physiological marvel allowing them to survive in the extreme Arctic winter. They slow down their metabolic processes to conserve energy, with heart rates dropping to as low as one beat per minute.

Diet

They are omnivorous creatures, consuming a diet of seeds, fruits, leaves, flowers, insects, and occasionally small vertebrates. They gather and store food in their burrows for consumption after hibernation.

Social Structure

These ground squirrels live in colonies and have complex burrow systems. They’re mostly diurnal, meaning they’re active during the day.

Breeding and Lifespan

Breeding occurs shortly after hibernation, usually in April or May. The female raises the young alone, and the litter size can range from 5 to 10 pups. The typical lifespan of an Arctic ground squirrel in the wild is around 3 to 6 years.

Predation

Arctic ground squirrels are prey for various carnivores including foxes, wolves, and birds of prey like eagles and hawks.

Climate Change Impact

Recent research shows that these squirrels are altering their hibernation patterns in response to climate change. Specifically, female squirrels are emerging earlier from hibernation due to earlier spring thaw, a change that could impact breeding patterns and the wider Arctic ecosystem.

These fascinating creatures continue to be subjects of scientific study, especially in the context of climate change and its impacts on Arctic ecosystems. Their ability to survive in harsh climates through remarkable physiological adaptations makes them unique models for understanding biological responses to extreme environments.

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