Hibernating Bears 'A Metabolic Marvel' A new study finds that despite lowering its metabolism by 75 percent, a bear's internal temperature barely drops. Bears also don't lose muscle mass or strength, and researchers hope the study — the first continuous monitoring of a bear in hibernation — will be a boon for human medicine.
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Hibernating Bears 'A Metabolic Marvel'

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Hibernating Bears 'A Metabolic Marvel'

Hibernating Bears 'A Metabolic Marvel'

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There are some advantages to being a bear. One is that you get to sleep through the winter. But there are some other perks you might not know about. NPR's Joe Palca does, and he has the bear facts.

JOE PALCA: It's relatively easy to study small creatures, especially the ones you can grow in the lab. But Brian Barnes wants to study bears. In particular, hibernating bears.

BRIAN BARNES: And we wanted it in natural conditions. And so these were the challenges.

PALCA: Did you go to them or did they come to you?

BARNES: They came to us.

PALCA: Their supply of bears comes from the Alaska Department of Fish and Game. They're typically bears who've taken a wrong turn and wound up in the middle of a city like Anchorage. In the summer, the bears live outdoors at the University of Alaska in Fairbanks, where Barnes works.

BARNES: And then we move them into a hibernaculum.

PALCA: Hibernaculum. Is that a real word? Or did...

BARNES: It is.

PALCA: ...you have to make one up?

BARNES: And the plural's hibernacula.

PALCA: In this case it's basically a big box, wired so it can measure things like the bears' temperature, heart rate or brain waves.

BARNES: We anticipated they might just tear the place up or go on strike or something. But they actually showed very natural behavior of getting ready to hibernate.

PALCA: As you can see on our website, when they start to hibernate, they curl up.

BARNES: They go to sleep. They begin to quiet their heart rate, slow their breathing, and their metabolic rate plunges.

PALCA: Barnes says the study he and his colleagues are publishing today in the journal Science marks the first time bears have been monitored throughout the winter. So what happens when hibernation starts?

BARNES: The bear will cool off just by a few degrees.

PALCA: From a normal temperature of about 99 degrees down to about 90 degrees.

BARNES: And yet its metabolic rate decreased by 75 percent.

PALCA: This was a surprise. No one realized that a bear could stay so warm while lowering its metabolism that much. It's a combination of very good insulation accompanied by bouts of shivering when the bear's internal temperature drops much below 90. Barnes says just about everything a bear does while hibernating is remarkable.

BARNES: Bears don't eat, drink, urinate or defecate for six or seven months.

PALCA: They make their own water, probably by metabolizing fat, and they get rid of wastes by breaking them down internally.

BARNES: They're a closed system. All they need is air. And they can do just fine. They're a metabolic marvel.

PALCA: One of the things bears do with waste is to use the calcium in it to keep their bones strong. A human who is bed-ridden for months will start to lose bone mass. But Seth Donahue says his research shows that doesn't happen with bears. Donahue is at the Michigan Technical University.

SETH DONAHUE: Basically we found out there were no negative consequences of six months of hibernation on the bone strength or mineral content.

PALCA: And it's not just the bones in bears that stays strong throughout the winter.

HANK HARLOW: They have this neat capacity to conserve their muscle mass, as well as muscle strength.

PALCA: Craig Heller from Stanford University is an author on the new bear paper. He says for people bedridden for long periods or people who are contemplating a long space voyage, such as going to Mars and back, figuring out how to make a human more like a hibernating bear would some advantages.

CRAIG HELLER: One would be lowering the energy requirement so you don't need as much food and water and resources, but another is just reducing the boredom.

PALCA: Of course, making an astronaut more like a hibernating bear won't solve all the problems of a long space voyage. A renegade computer could still cause trouble.


KEIR DULLEA: (as Dr. Dave Bowman) Open the pod bay door, Hal.

DOUGLAS RAIN: (As HAL 9000) I'm sorry, Dave. I'm afraid I can't do that.

PALCA: Joe Palca, NPR News, Washington.

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