February 2021: New England’s Hibernators
File:Groundhog With Burrow Material.jpg

The groundhog is one of Connecticut’s two hibernators. This one is gathering materials for its burrow.

I know some people wish they could retreat into their bedroom, curl up under the covers, and hibernate until the warm days of spring beckon them. Not so for us, being sub-tropical mammals. However, certain animal species in New England have adapted to winter’s cold in different ways. We’ve talked about frozen frogs and the winter habits of the painted turtle. Now, let’s turn our attention to mammals!

The only two Connecticut mammal species considered true hibernators are woodchucks (also known as groundhogs and marmots), and bats. I know, I can practically hear some of you saying “What about bears?” Well, what about bears?

Turns out, bears can come in and out of dormancy, the same way chipmunks and raccoons can. How does this differ from hibernation? Well, if dormancy was a spectrum, hibernation would be on one end. Dormancy is a period of quiet, restive inactivity. Hibernation includes this, and severe metabolic depression: their metabolism slows, as does their heart rate, and their body temperatures drop to approximate the external ambient temperature. (Hibernation is generally used to describe warm-blooded animals in this state, as they can maintain physiological stability, unlike cold-blooded animals whose internal temperatures depend on external factors.) The body temperature of bears going into dormancy will lower by only a few degrees celsius.

The greatest visible indicator of hibernation is the inability to rouse in and out of it. To enter hibernation, an animal must radiate heat from its body so the body temperature can drop. With a large animal like a bear, it would take a considerably longer time to expel this heat. To emerge from hibernation, the body temperature has to increase. Again, in bears, this would take hours. So instead, bears enter a period of dormancy where their metabolism and body temperature lowers, but not to the extreme required for hibernation. If you were to come across a bear during dormancy, the bear can awaken and defend its hibernaculum just fine. An animal in true hibernation would not react to to the sound of your footsteps, or even to poking, though it may start the process to come out of hibernation with this sort of stimulus.

Three placental mammal groups hibernate: rodents, bats, and hedgehogs. Bears, raccoons, and skunks? They’re just taking a good, restful winter nap.