I guess it's Mother Nature’s little way of saying, “Hey, it's time to take a break.”
For those you living in a cold weather environment (such as myself), this tactic, behavior, trait or whatever you want to call it, doesn’t seem like such a bad idea. Ya know, fatten up during the summertime on your favorite foods and beverages and then when winter rolls around, lay yourself down and take a nice long nap. And then, POOF!, when you awake, everything is fresh and new again. In fact, I, as member of the human race, tend to do the exact opposite. I seem to put on the pounds during my idle winter months. I guess this is because I’m not a big fan of winter sports or activities and am pretty much stuck indoors in front of my television, laptop, or curled up with a good book. There are no lawns to mow, no kids soccer games to go to, no golf, softball, baseball, swimming or any other activities that I usually like to partake in. But enough about myself already, why don’t we take a look at hibernation as it pertains to our friends in the animal kingdom.
What is it?
A very loose definition of “hibernation” might be described as a state of dormancy or torpor. Animals use this tactic during the winter months when little or no food is available. Any effort to obtain what food is available actually causes the animal to expend more energy than the food itself is worth.
Actually, there are a couple of different kinds of hibernation. You’ve got your “true” or “deep” hibernators in the form of woodchucks, some ground squirrels and bats. All of these guys experience huge drops in heart rate, body temperature, respiration and metabolism. Because they use so little energy they’re able to remain inactive for long periods of time without fuel. In the case of the woodchuck, their heart rate drops from about 80 beats a minute to 4 or 5 beats a minute. Its body temperature drops from a comfy, cozy 98 degrees Fahrenheit to about 38 degrees. His/Her choppers, which continually grow during the summer, stop growing while he/she hibernates. Members of these “true” hibernators are almost impossible to wake up.
Next you’ve got your so-called “light sleepers”. Bears, skunks, raccoons and the like generally fall into this category. The celebrity of the bunch, the bear, body temperature will only fall about 12 degrees or so. His heart rate, normally about 40 to 50 beats a minute, drops down to anywhere from 8 to 10 beats a minute. While its true that they can go about 100 days or so without eating, drinking, urinating, defecating or getting some exercise, in contrast to the “true” hibernators, and while it is a slow process, can be easily awakened.
How do they prepare to hibernate?
In the case of the bear, they quite simply, gorge themselves. When food is plentiful, they have been known to put on as much as 30 pounds per week. This enables them to store up huge layers of fat. As fall approaches the bear begins to prepare his den (usually a burrow, cave, or tree trunk) by raking in dead leaves and other plant material. This provides him with some insulation against the coming cold weather.
What happens when they hibernate?
Relatively little is known about what goes on during the period of hibernation. Remember all those huge layers of fat we spoke about?. Well, as the bear begins to hibernate, the fat breaks down and supplies the bear with water and about 4,000 calories a day. Protein is supplied from the breakdown of muscle and organ tissues.
Unlike us humans, who also breakdown muscle and tissue during periods of starvation, the bear is able to replenish itself. It does so by using nitrogen that is stored in its urea to build new protein.
All in all, bears lose anywhere from 15 to 40 percent of their body weight during periods of hibernation.
Probably the most amazing thing the bear does during hibernation is something called “delayed implantation.” Your average she-bear will carry around a fertilized egg inside her for many months. Amazingly, the egg will not attach itself to the bear's uterine wall until some sort of body signal is given. When said signal occurs, it will develop into a fetus. This gives the bear cub the maximum chance of survival.
How do they know when it's time to hibernate?
It's in the genes. Maybe, more accurately, it's in the blood. All hibernating animals have one thing in common. They have a substance in their blood known as the Hibernation Inducement Trigger (HIT). Little is presently known about it but experiments have shown that if you were to take the blood from a hibernating squirrel and inject into an active squirrel during the spring, the active squirrel will go into hibernation.
Any more research being done?
You betcha! NASA has shown some interest in putting more research into the benefits of hibernation for humans in the event that we ever become capable of long distance space travel. The United States Army has funded research over the years to “hibernate” wounded soldiers, thereby slowing their metabolism when medical facilities aren’t readily available. Organ donor programs are also interested in hibernation in order to preserve them for transplant surgeries.
For what its worth, I would say there still a lot to be learned and benefits to be gained from something so simple as a nice long winter nap.