Wood Frog

Who’s Hibernating in the Valley?

Cartoon bears in nightcaps snoozing in an over-stuffed bed define how many of us envision this miracle of nature. But as it turns out, most bears don’t truly hibernate—but other creatures do.

Many bears experience a state of dormancy called torpor, a type of light hibernation. Torpor is characterized by the ability to wake up quickly to avoid threats, perhaps go out for a snack, and sleep for short lengths of time according to conditions. Part of this distinction also may have to do with size. As a rule of thumb, the smaller the animal, the more likely it is to be a true hibernator.

Groundhogs and Wood Frogs and Bees….oh my!

In the Southeast United States there are plenty of examples of true hibernators, including groundhogs. A member of the squirrel family, the groundhog spends the warmer months building fat reserves to survive the cold weather and lack of food. They can sleep snug in their burrows for up to five months, an important distinction on the hibernation checklist.

During this time, a groundhog’s heart rate may plummet from 80-100 beats per minute to 5-10 beats a minute. Likewise, their body temperature can decrease more than 60 percent, and their breathing can drop from 16 to only two breaths per minute.

Other hibernators include some surprises. Consider the wood frog, who often spends the winter in leaf litter. Its heart can completely stop beating during hibernation, and a portion of its body freezes. Although the process sounds painful, the wood frog doesn’t seem to mind. As soon as spring arrives, this hearty frog thaws out, finds some food, locates a pond and begins mating.

The bumblebee is another astonishing hibernator. In autumn, the queen digs underground to hibernate by herself as the rest of her colony dies. In spring she makes her way out and begins laying a new workforce, new royalty, and male bees.

Torpor – a lighter sleep

Meanwhile, other mammals take advantage of torpor. Unlike hibernation, torpor is thought to be involuntary. Animals such as racoons, skunks and even some bats benefit from this type of slumber, which is not as deep as that of true hibernators.

Skunks live in their dens year-round, but stay there more continuously in cold weather. Because they enter a state of torpor instead of hibernation, they can wake themselves on more temperate days and climb out to forage. Grubs are one of skunks’ favorite foods. This delicacy is most plentiful in the winter, creating an “all-you-can-dig” buffet for these nocturnal animals, who also enjoy unsecured garbage and pet food left outside.

Bats are popular animals that many individuals associate with hibernation. However, research may suggest that some bats leave their shelters on a regular basis during winter. 

“It’s important to distinguish that each of the 16 bat species in the TVA region has specific winter habitat requirements,” says Jesse Troxler, TVA biologist. “For example, eastern red bats use trees and leaf litter and rarely enter caves. Gray bats, however, are known to winter in caves.”

Troxler says that data on hibernation vs. torpor is far from complete. “There is a lot of conflicting information out there about whether species are ‘true hibernators’ or use torpor. In the end, it may, in fact, be a spectrum.”

One thing’s for certain, this issue is on the radar of many biologists who are gathering data to understand more. In the meantime, here’s to the variety of animals in our part of the country and the interesting ways they spend their long winter nap.

If you come across an immobile animal, leave it alone! That dead-looking creature might wake out of its torpor and decide to bite you. For other tips on staying safe on public lands, Read more about other tips on staying safe on public lands.