Reprinted from a Febr 11, 2007 column in the Morgantown Dominion Post
At the time of the year, when most wildlife is walking a thin line relative to survival, black bears are hibernating and staying relatively comfortable. No food shortage for them in winter, because they aren’t eating.
We used to say that bears were not true hibernators because their body temperatures did not drop significantly in winter dens as other hibernators did. However, that has changed and we now consider bears as hibernators even though they differ from other hibernators. You see there are two types of hibernating animals in West Virginia. In the first group are mammals who hole up and their body temperatures drop. Their metabolism slows down and their heart rate also decreases. Chipmunks, bats and woodchucks are in this group. A woodchuck lowers its heart rate from 80 beats a minute to 5 beats a minute. His body temperature drops to just above freezing. If you look at a hibernating woodchuck, it will appear to be dead. But here is the difference in true hibernators and black bears. True hibernators awaken every few days, their body temperature goes up, and they move around a bit in their burrows and urinate.
Black bears have a much bigger surface-to-mass ratio, and a thicker fur, and when they hibernate their body temperature doesn’t drop as much. The normal summer temperature for a black bear is 100 degrees, but they only drop to 88 in hibernation. Also their metabolic rate decreases a great deal and they do not eat anything from mid-to-late December till early-to-mid March when they come out of hibernation. This year was a bit different for some bears. Because of the unseasonably warm weather some did not go into hibernation in December. My friend Kevin Turner saw a sow and three yearling bears at a feeder on his Aurora farm during the warm spell we had the second week of January. Since sows normally give birth in their dens around January 10-15, my guess is that pregnant sows were hibernating even with the warmer temperatures. Obviously some bears were still out roaming around during those warm January days here in West Virginia.
When a bear hibernates, the breathing rate decreases; however, since their body temperature is close to normal, they can be disturbed rather easily, so poking around a bear’s den is not something you want to do. Most times there wouldn’t be a problem as in my experience a hibernating black bear just opens its eyes and looks at you without much reaction. However, I just read where two surveyors in Alberta stumbled upon a grizzly bear den two weeks ago and were badly mauled. Now a grizzly bear is much more aggressive than a black bear, but even so, one should let sleeping bears lie.
When the world’s top black bear biologist, Dr. Gary Alt was doing his doctoral work here at West Virginia University, I learned that the medical world was going out with Gary to bear dens to collect various types of data. I remember they also were looking at the sows milk, though I don’t remember why. But there are other things going on out there that could help humans. One fact is that hibernating bears are living off body fat, and their cholesterol levels double from summer levels. Yet, bears don’t get hardened arteries. They also produce a bile substance that when given to people dissolved gallstones.
I also remember that the NASA doctors visited Gary on his winter treks to bear dens. Since astronauts are fairly immobile in space, they can lose muscle and bone mass. That doesn’t happen with hibernating bears. For long interplanetary flights, adding weight for food might be a problem for our rockets. If we could place a space traveler in "hibernation" then such problems would be reduced. Hey, they are already doing it in Startrek. Seriously, hibernating bears might provide clues as to how we can better deal with the conditions faced in space travel.
Hibernating bears do not urinate. They burn body fat which yields carbon dioxide and water and energy. The water produced does not leave the body, but remains in the blood. It is a finely tuned system that is so well evolved that hibernating bears do not need to drink or urinate. They sort of recycle the waste, producing needed energy and water. If we stopped urinating we would poison ourselves with urea. When other mammals burn fat as bears do, there is a toxic by product built up, called ketones. For some diabetics, ketones lead to diabetic coma. We don’t know how bears handle ketones, but such knowledge could benefit humans.
Doctors were also interested in the ability for bears to lower their metabolism for months without negative effects. When humans are placed into inactivity via drugs, they lose calcium. Bears don’t. How do they do that? If we could induce a state similar to bear hibernation, it could be invaluable for burn victims, or people with head trauma. Why? Because everything could be slowed down, but with no buildup of toxic substances and no loss of calcium.
As I write this, it is extremely cold outside. I’d love to just sleep through these periods, but Cathy wants me to shovel the sidewalks. No hibernating in this house. Darn.
