Deep Sleep, Torpor, or Hibernation? It's Naptime in SW Colorado
Durango Herald, Dec 14, 2006
Melissa Paxton, Development Coodinator

Ground squirrels horde as much food as possible, so when they wake up during winter naps they have something to gnaw on. Courtesy of DNS.

If you ask your resident 6-year-old what she knows about hibernation, she might tell you something similar to what my friend, Grace Frideger, told me recently:

"It's when bears get lots of food and then they wait until winter starts and it is cold outside and then they go in their caves and go to sleep. Oh, and raccoons hibernate, too. Then in spring, the bears get out of their bear caves and they go exploring because they haven't been out in a really long time, and I think they yawn a lot when they wake up."

I'm pretty sure we learned the same thing when I was in first grade, too. I definitely remember being careful to be quiet as I scrambled over, under and around the granite boulders, icy overhangs and shallow caves of our deeply forested backyard in hopes of not waking up a sleepy spring bear.

But while bears, badgers, raccoons, chipmunks, squirrels and skunks do some pretty deep napping come winter, scientists these days tend to call this group of mammals' sleep time "torpor" - and they save the term "hibernation" for true hibernators.

The difference? Mammals who spend time in torpor never reach the deep sleep that hibernators do. Squirrels and chipmunks may eat lots of acorns, nuts and seeds in the fall, but their main objective is to hoard as much food into their burrows as they can fit. That way when they wake up from their winter naps - as they do every week or so - they can have a snack before succumbing again to sleep.

The true hibernators of Europe and North America - bats, hedgehogs, prairie dogs, groundhogs (no wonder Punxsutawney Phil always looks so grumpy!) and marmots - really do sleep their winters away.

Hibernating bats, which spend their winters grouped together in caves or stuffed into rocky crags and cracks, can regulate their body temperatures to exactly match the freezing temperatures outside. They can also set their hearts to beat as little as eight times per minute and only need to take a breath once every two minutes.

White-tailed prairie dogs - and their young - can hibernate for up to five months, stuffing themselves for weeks ahead of time on grasses and insects, in order to store up a nice layer of warm, energizing fat.

Known as woodchucks, marmots and groundhogs, every species of marmota is a true hibernator. In fact, these furry rodents sleep so deeply that if you stumbled across one on a snowy hike, you could literally pick it up by its icy tail, swing it over your head, and it wouldn't move a muscle. (Of course we don't recommend you add this to your list of winter hobbies.)

While it appears that animals that go into torpor use many of the same internal regulators to slow their bodies down as true hibernators do, the difference seems to lie in the waking-up process. Animals in torpor, such as bears and badgers, might be a bit groggy when awakened, but they can actually get moving pretty quickly. A true hibernator, such as the marmot, may take days just to squeeze open one eye!

Knowing all this now, it makes me glad I never had a torpor-ific bear encounter.