Do grizzly bears really hibernate? The answer's complicated

If you're talking to a scientist, try not to use the words "bear" and "hibernate" in the same sentence.

It's common knowledge that bears enter a deep sleep during winter, but what's the proper terminology for that? Calgary naturalist Brian Keating says it's more complicated than many might think.

"It's been argued as to whether or not it's a hibernation with bears," he said. "They definitely go into what I would call a hibernation. Professionals, I guess, call it a torpor."

Hibernation and torpor are similar concepts, in which mammals enter a state of reduced heart rate and body temperature.

"What forces these animals to go into hibernation is they can't make a living in our ridiculously difficult winters, so they go to sleep," Keating said. "Not a bad idea."

But what scientists call "true hibernation" is experienced by only a few animals in Alberta, primarily ground squirrels and marmots.

"Ground squirrels will burrow down into the ground and sustain themselves in their burrow in an ambient air temperature about a degree above freezing," Keating said. "They let their body go down to that kind of temperature, so they are basically in a state of suspended animation."

Hoary marmots and Columbian ground squirrels, both commonly found in Alberta's mountains during the warmer months, spend about three-quarters of the year in hibernation underground.

"It takes a long time — perhaps half an hour or so of shivering and shaking — to get their muscles warmed up before they can actually be active enough to move around to any great degree," Keating said.

Keating recalled visiting a friend's lab in Manitoba, where ground squirrels had been put into hibernation. The friend pulled out a hibernating ground squirrel, and it began to shiver and shake as it knew it was being handled, Keating said.

It takes a great deal of effort and energy for an animal in true hibernation to wake up.

That's not the case with bears.

"If you were to climb into the den of a bear, that bear can come out of its state of torpor rapidly, and would probably end up ripping off your face," Keating said.

Torpor, which is also experienced by skunks, raccoons and some bats, is not nearly as deep of a sleep as true hibernation.