Bear hibernation like no other

Animals have own way of shutting down for winter

Gary Gerhardt, Rocky Mountain News

Saturday, February 5, 2005

Wouldn't it be cool if we could hibernate like some animals do in winter?

When the temperatures dip and the days grow shorter, animals have three options: hibernate, migrate or grow thick furry coats and tough it out. Unless they are those birds that stick around, but who understands birds anyway?

We have much to learn from the hibernators, especially the bears. They don't urinate, defecate or lose much muscle mass or strength while spending six months or more in a den without physical activity or nourishment.

If we could understand how they do it, think of the possibilities for astronauts to make space travel to distant planets plausible.

Or in cases of severe injuries, putting the victims into protective hibernation might keep them alive until medical assistance arrived.

And once they were in a hospital, their muscles and circulatory system wouldn't start to rebel and turn against them.

And above all, think of vacations where the kids could be put in a state of hibernation. No more "Are we almost there?"

Hibernation always has been a bit of a puzzle. Most stories I've covered were working with bears, and bears just don't act like a hibernating animal should.

Take the ground squirrel. When they go dormant for the winter, their heart rate drops from 300 beats a minute to just three or four.

Their body temperature is only a few degrees above ambient temperature and their oxygen consumption drops to 2 percent of normal.

They are so deep in their sleep that you can pick one up and toss it around without arousing it.

But I wouldn't advise that with a bear - for a couple of reasons.

Aside from the weight, bears don't drop into that deep hibernation.

Bear expert Roger Powell of North Carolina State University said once a black bear goes into hibernation, it dozes many months with a body temperature of 88 degrees or higher, which is within 12 degrees of summer levels.

Tom Beck, the retired bear biologist for the Colorado Division of Wildlife, said bears almost always were fully awake when he crawled into their dens to stick them in the rump with a jab stick - a long stick with a tranquilizer dart on the end.

Unlike some small mammals that can take a half-hour to many hours to get their hearts started and warm blood pumping to the brain and muscles to arouse from hibernation, it would take a bear days to do that if it went into a deep hibernation.

"If a bear was a deep hibernator and it was attacked by a wolf or cougar in its den, it would be dead before it could respond," Beck said.

But with the ability to sleep lightly through the winter, it can awaken almost instantly and be ready for fight or flight if danger approaches.

I remember one example in particular.

I accompanied Hank Harlow, professor of physiology and zoology at the University of Wyoming, trapper Lyle Willmarth and others in the Arapaho National Forest near Hot Sulphur Springs to dig a bear out of a den.

It was a sow that had been radio-collared so they knew where she was sleeping.

Harlow was funded by NASA, the National Science Foundation and the Colorado Division of Wildlife to study how bears remain without moving in a den for six months and not suffer muscle atrophy.

The key lies in a process called "protein turnover," Harlow said, in which bears don't drink water or urinate during their months of confinement but have a unique digestive system that cycles their waste back into protein without loss of muscle mass or strength.

"If we can figure out how they do that, think of the medical implications for bedridden hospital patients, astronauts in space, even people that must keep broken limbs in casts for protracted time," Harlow said.

They knew where she was denning in a hollow near some aspen, and as we slid down through the snow to the area, there was a lot of apprehension that she'd bolt.

Another danger is that she would be jabbed, but push her way past and run down the hill for a couple of hundred yards before the drugs took effect and we'd have to carry her back home after the experiments were finished.

A knot of people semi-circled the mouth of the den, and as I remember, if Willmarth took a short-handled shovel and started in.

As soon as she was exposed, she started out and everyone grabbed a shovel, piece of wood, a backpack and whatever could be used to hold her in while she was jabbed.

Luckily she calmed down and ended up having to be dragged out of the den.

So how does hibernation work anyway?

Well, the London Times had a pretty good piece about Matthew Andrews, associate professor of genetics at North Carolina State University, who spent five years studying it and identified two genes - PL and PDK-4 - that appear to mastermind hibernation.

He said one of them stops carbohydrate metabolism, which ensures the glucose that animals have stored in their body from their last meal is preserved for use by the brain and central nervous system.

The second gene controls the production of an enzyme that breaks up stored fatty acids and converts them into usable fats for fuel. As a result, the animal can sustain itself on its stored fat.

I have half of that mastered - the stored fat part.

Hibernation in animals is characterized by huge drops in heart rate, body temperature and metabolism, resulting in long-term dormancy. In this state, body temperature is only a few degrees above freezing, oxygen consumption is down to 2 percent of normal, and the heart rate drops from up to 300 beats a minute to just three or four.

Researchers found the genes can be made to work in similar ways in humans. The PDK-4 gene, for example, is switched on by starvation, when its job is to conserve glucose.

Now if they can only figure out what triggers the genetic process that starts it all - and ends it after the season.

If you go to the Denver Zoo, the bears will be awake and playing with their feet in the middle of the winter. That's because they're fed.Hibernation Facts

There are two kinds of hibernators:

• True hibernators whose body processes shut down. They have few heartbeats per minute, body temperature drops to slightly higher than the surroundings.

• Others such as bears and raccoons whose body temperature and blood pressure remain somewhat constant and they slumber lightly.

• Hibernators include chipmunks, other ground squirrels, marmots, woodchucks, skunks, bats, other rodents.

• They say the poor-will is the only bird that hibernates. It tucks into rocky cracks or rotten logs and falls into a deep torpor.

• Insects die in the fall and their eggs survive in a state of suspended animation called "diapause," which is a sort of super hibernation with the insect's metabolism dropping so low it is only minimally alive.

• The only adult insect that hibernates is the bald-faced hornet queen that crawls under a rotten log and is insulated by the snow.

• Cold-blooded animals such as fish, frogs, snakes and turtles find shelter in holes or burrows, and spend the winter inactive or dormant. When the weather gets cold, they move to the bottom of lakes and ponds where frogs, turtles and many fish hide under rocks, logs or fallen leaves or bury themselves in the mud.Sources: Owashtanong Islands Audubon Society; Nova Online.

gerhardtg@RockyMountainNews.com or 303-892-5202