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Good Question: How Does Hibernation Work?

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(credit: CBS) Jason DeRusha
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By Jason DeRusha, WCCO-TV

MINNEAPOLIS (WCCO) — Most of us have a cartoony image of hibernation: Yogi Bear snoozing away under the giant Redwood tree. But in Ely, Minnesota, Lily the bear is showing signs of labor. She’s about to give birth, in the middle of hibernating. So what happens during hibernation?

“I’ve been doing hibernation research for the past 12 years,” said Dr. Paul Iaizzo, a University of Minnesota heart physiologist.

Iaizzo wants to heal humans, but specializes in bears.

He and researchers from the Minnesota Department of Natural Resources and Medtronic put heart monitors on hibernating bears. They measured heart rates at around 5 or 10 beats per minute during hibernation.

“When they inhale, their hearts go up to 60 beats, then go right back down. They’re very efficient at taking in all that oxygen and conserving all that energy,” said Iaizzo.

Bears don’t eat or drink anything, so they can lose around 60 pounds of fat during hibernation.

“What we’re trying to understand is how they don’t lose muscle mass,” Iaizzo said.

If you slept for 5 months, you wouldn’t be able to move afterwards. But bears are able to run out of their dens when they wake up in the spring.

“You break your arm and have a cast, that’ll shrink to 50 percent with a couple months. A patient in a hospital bed, they’re losing muscle mass and strength. It’s interesting that bears don’t do this,” he explained.

Some scientists don’t think bears technically hibernate, because their body temperature only drops about 10 degrees and they can wake up if a predator (like a wolf) looms.

“You can wake up a bear. Bears still have this intact fight or flight instinct. Bears have the ability, within minutes, to respond to a predator and danger,” he said.

Another thing that is unique about bear hibernation is that bears can give birth during that time.

“It’s a typical phenomenon,” said Iaizzo. “There’s a bump in heart rate, then she goes back into hibernation. The cubs must be suckling and feeding during the hibernation of this mother.”

Scientists are looking at bear genetics, compounds in the plasma, trying to unlock the mystery of hibernation.

“They really aren’t losing much strength at all, which is amazing. If you could figure out how to do that for patients, it would be pretty exciting,” Iaizzo explained.

Other animals do hibernate. Gophers burrow into the ground, and their bodies come close to the temperature of the air in there. Some types of bats, frogs, snakes and ladybugs also hibernate.

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