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Do Bears Actually Hibernate?

I was talking with some friends the other day, and they mentioned that they might start putting out their birdfeeders a little earlier than usual, especially since the weather has been milder than normal. The thought of putting out bird feeders stuffed with sunflower seeds also brought up another topic — bears and birdfeeders.

I mentioned that I hadn’t put out feeders for the past couple of years mainly because bears, on several occasions, have torn our feeders down and, in some cases, damaged them beyond repair. We have also had several suet feeders pulled down and taken off to the woods, never to be found again.

Eventually, our conversation rolled around to the subject of bears instead of birdfeeders and, more specifically, the subject of hibernation. Many people think that bears hibernate during the winter months, but the fact is that bears are not true hibernators.

While bears are not true hibernators, our common groundhog or woodchuck is a true hibernator.

So why do animals hibernate?

Some of our wildlife isn’t equipped to handle the cold temperatures, and another big problem is the lack of food supply during the winter months.

The groundhog, for instance, is an herbivore — they eat mainly plant life. Obviously, not much is available during the cold winter months, and they would likely starve to death. During hibernation, a groundhog will burrow deeper into the ground, and its heart rate will drop to five beats per minute. Also, it will only take about two breaths per minute, and its body temperature may even drop below freezing. The groundhog survives the low body temperature because salty body fluids work to prevent tissue crystallization.

So, if bears don’t hibernate, what do they do come winter? Bears do den up and become somewhat dormant. A bear’s den, by the way, is not necessarily a cave, but in reality, it may be a hollow log or tree, a crevice in a rock ledge, beneath fallen tree roots, a drainage culvert, or it may even be a depression in the ground surrounded by brush. Someone recently told me of a bear that denned under a porch. While bears do become somewhat dormant while denned up, they actually lapse into and out of a deep sleep. Body temperature does drop, but it’s not a drastic decline. Respiration and heart rate might decline somewhat, but not to the decline of true hibernation. Another very interesting detail regarding a bear in a den is that no waste is found in a den; they do not urinate or defecate while in that “torpor” or inactive state. It turns out that bears are actually able to turn their urine into a protein through a recycling process. My guess is there are a lot of humans out there who would like to cash in on that process.

Bears have been known to go for long periods without leaving their dens and are capable of going two or three months without eating or drinking.

While it’s true, they may not leave their dens for long periods; it’s also true that during warmer periods, they may arouse and leave their dens for a time to search for food. I would not be a bit surprised that some bears, especially males, may have been on the move outside their dens more than once this winter since we’ve had some very mild, even warm days.

I was hiking through the woods several years ago in early spring on my way to a trout stream when I discovered a bear in a “den,” and I got a quick preview of all the stuff I just talked about regarding a bear in a den. The large male bear, about 400 pounds, was curled up under a large fallen tree. I moved up closer to take a picture when the bear suddenly looked up at me. I quickly backed off and went on about the business of trout fishing.