Climate Change Is a Wake-Up Call for Hibernating Squirrels

When winter arrives in northern Alaska, Arctic ground squirrels dig burrows three feet beneath the surface. Then, as temperatures dip below freezing, they snuggle in for eight months of hibernation. During that time, their bodies go through drastic changes to keep them alive—including dropping their body temperature to a frigid 27 degrees Fahrenheit. They finally emerge in the spring and begin searching for food and mates.

But as the planet warms because of human-caused climate change, the rodents’ hibernation patterns are getting thrown off. Females are leaving their burrows earlier and earlier each spring. Their male counterparts, on the other hand, don’t seem to have changed when they end hibernation. This mismatch could eventually spell trouble for the species’ reproductive success, according to a new paper published last week in the journal Science.

To understand Arctic ground squirrel patterns, researchers analyzed long-term climate and biological data gathered over the last 25 years in the Alaskan Arctic. They found that females are now ending hibernation up to ten days earlier than they used to, likely because the soil is thawing sooner.

This ten-day shift over a period of 25 years might seem insignificant, but “in terms of climate, that’s incredibly fast,” as study co-author Cory T. Williams, a biologist at Colorado State University, tells the New York Times’ Mélissa Godin.

Though Arctic ground squirrels still have a strong population—the International Union for Conservation of Nature lists them as a species of least concern—any changes to their numbers could have ripple effects up the food chain. Many Arctic predators rely on Arctic ground squirrels for food, including eagles, wolves, hawks, falcons, bears, ermine and foxes.

Previously, males would come out of hibernation one month before females did, because male Arctic ground squirrels need time each spring to become sexually mature again. Their testicles shrivel up in the fall, then regrow and descend when they end hibernation. In addition, their testosterone levels plummet during hibernation, then spike again each spring.

While the males still emerge from their burrows first, that window before the females surface is shortening. If the recent trend continues, someday, females could awaken to a world in which males are not yet reproductively mature, which could throw off their mating cycle.

For now, however, researchers say the species may get some benefits from females ending hibernation earlier. For one, they don’t need to use up as much of their fat reserves while hibernating, which gives them a bit of a head start in the spring. They can also start looking for seeds, berries, roots and shoots earlier. Together, scientists say these changes could result in higher survival rates and more robust litters.

However, emerging earlier in the spring means female Arctic ground squirrels are vulnerable for longer to hungry predators. This, in turn, might lead to predators adapting their own behaviors and reproductive cycles to keep pace with an earlier supply of prey.

In short, scientists still don’t fully understand the ramifications of rising temperatures in the Arctic, which is warming faster than other parts of the world. It’s possible that male Arctic ground squirrels will eventually also end hibernation earlier, but only time will tell.

In the meantime, the study provides evidence of climate change’s rapid “effects on ecosystems within the time span of people’s lives, including young people,” as study co-author Helen Chmura, an ecologist with the U.S. Forest Service, tells the Agence France-Presse’s Issam Ahmed.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.