COMMENTARY BY DR. DAVE SAMUEL
You often hear that black bears are hibernators, and although they sleep in winter, they aren’t true hibernators. Hibernators survive the winter by crawling in a hole, lowering body temperatures, not eating, and not moving until warm spring temperatures arrive.
Black bears do some of that, but they don’t go into a long, deep sleep. This lighter state of sleep is called torpor. In torpor, bears crawl into some protective area, slow their heart rate, breathing rate, and metabolic rate. Their temperatures may drop a little, and their sleep is a little deeper than normal. But if you enter a den in winter, bears perk up quickly.
During cold winters, bears in torpor don’t need to eat. Their fat provides water and calories for the body. Females (sows) give birth during torpor and studies done by Dr. Gary Alt during his doctoral program at WVU showed that almost all females in Pennsylvania (where the research was done, and West Virginia bears are probably the same) give birth within a week of Jan. 15. You might wonder how Gary figured that out. He had several females radio-collared over 10 years of data collection and that allowed him to know where they denned in winter. Then he would visit those dens every few days and put a microphone into the den and listen for sounds the cubs made. Just one of many things Gary learned about bears during those ten years.
By the way, when the cubs are born they are very small and they immediately attach to the mother’s teats. They do not go into torpor, they just nurse and grow quickly.
Bears do not always den in winter. If the temperatures are mild, and they have access to food, they stay out. However, pregnant bears always go into torpor, and all bears do so when the weather gets bad. Several years ago, I bowhunted bears in Alaska and met a bear biologist when I checked in my harvested bear. I was puzzled why the bear I harvested had such a small skull for being such a large-bodied bear. He told me it was because in that part of Alaska the bears denned for as long as seven months. When not in torpor, they had good feed and grew big bodies, but being in hibernation for long periods meant smaller skulls.
Do all bears use the same type of denning sites? In many places, including West Virginia, black bears will dig around the roots of overturned trees and crawl in for the winter. However, they can use road culverts or small caves in rocks. We learned in Pennsylvania that denning in holes they dug at the base of overturned trees can lead to drowning. Heavy spring rains can lead to such dens quickly filling with water and as many as 25% of all cubs born in such dens drown.
Tennessee bears tend to go into torpor in big trees. They climb up dead or dying trees and crawl into the hollow centers. Bears in Pennsylvania, and I’m assuming West Virginia, sometimes will just crawl under a brush pile to sleep. Snows provide them insulation.
When the weather starts to warm up a bit, the females will leave their den and seek food, then return to the cubs. With further warmth, they then take the cubs and leave the dens for good. One last thing: The cubs stay with the female through the summer and fall, and den with their mothers the second winter. If a mother has three or four cubs (now yearlings), a den can get pretty crowded that second winter. When she comes out of torpor that second spring, she’ll drive the yearlings off, because June is breeding time. And so the cycle continues.
So, there you are. It’s how bears survive the winter and the system seems to work for them quite well. With this darn COVID, some of us are getting the feeling that we’re hibernating this winter. Hang in there. Wear your mask and get vaccinated when available.
