Hibernation: Some They Do, and Some They Donít

by James P. Gass

As the air gets colder, the nights get longer, and the days get shorter, have you noticed feeling a little more sleepy than usual? Do you have trouble getting out of bed in the morning? In fact, do you just want to stay there and sleep the whole winter through? Fear not, oí two-legged mammal, youíre not alone. Itís time to hibernate.

Though there are several furbearers in southern New England that hibernate in winter, itís not true that all of them do. True hibernation is a state of deep sleep, or torpor, where an animalís respiration, temperature, and heart rate become drastically reduced. The idea is to conserve as much energy and body fat as possible until warm weather returns the spring. Itís a survival technique that has also been used for millenia by reptiles and amphibians, including Blackstone Valley locals such as spotted salamanders, wood frogs, spring peepers, and painted turtles.

Among the mammals of the Blackstone Valley, only woodchucks, bats, and jumping mice actually hibernate. All others, including deer, rabbits, bobcats, mice, canines, squirrels, and members of the weasel family, remain active throughout the season. Certain animals such as chipmunks, raccoons, and skunks periodically go into dens and become dormant during periods of severe weather, then emerge again once conditions improve. A good book such as Tracking and the Art of Seeing by Paul Rezendez (1999) will help you ďreadĒ the tracks and signs of these non-hibernating animals as they go about the difficult business of surviving the winter.

Woodchucks spend all summer and fall building up body fat for their long winter nap. They dig burrows (or dens) up to six feet deep and as long as forty feet. They often have a den for summer and another for winter. The summer den is dug in an open field, but the winter den is excavated in a nearby wooded area. The winter den contains a hibernation chamber, which the woodchuck enters in early November. Once there, the Ďchuck goes into a deep sleep, and doesnít wake until February. The legend of a woodchuck emerging from its winter den, seeing its shadow, then going back for another six weeks is, of course, a myth, as alas, woodchucks are not particularly intelligent animals.

According to Alfred J. Godin in his book Wild Mammals of New England, little brown bats and big brown bats both winter in the Blackstone Valley, but big brown bats are the ones more likely to hibernate in your attic. Little browns prefer caves and other natural settings, sometimes flying great distances to find suitable sites. Both species hibernate in colonies. And although bats go into a torpor when hibernating, they do not go into the type of deep sleep of some other mammals. When disturbed, they may awake and fly off to another spot. Some other bats found in our area include Keenís Myotis, silver-haired bat, and hoary bat. And no, bats do not deliberately fly into your hair!

Jumping mice look something like miniature kangaroos when startled, hopping away on large, hind legs. The two species that occur in the Blackstone Valley are the meadow jumping mouse and the woodland jumping mouse. At first glance they look very similar. Both have a body about 3-4 inches in length and a scantily haired tail that gets about 6 inches long. But the woodland jumping mouse has yellowish sides and a white-tipped tail. According to RIDEM wildlife biologist Charles Brown, the meadow jumping mouse is the more common of the two and can be found throughout southeastern Massachusetts and Rhode Island. As their names imply, one is found in fields and wet meadows, while the other prefers woods. But both animals are ďprofound hibernators,Ē fattening up for two weeks before going into their burrows for a deep sleep that can last as long as six or seven months.

Black bears, though they are not true hibernators, are deep sleepers in the extreme northern part of their range, which includes Alaska and Canada. There they may sleep uninterrupted for up to six months at a time. But they do not do this in southern New England. According to Rezendes, while snoozing in itís winter den, a black bearís heart rate drops from 40 beats per minute to 10, and itís oxygen intake is cut in half. But its body temperature drops only a few degrees, so if a sleeping bear is disturbed, it can wake up fairly quickly and become dangerous. Although the Blackstone Valley has few, if any, resident black bears, young, wandering males sometimes show up at area parks and wildlife refuges. But since bear populations are currently expanding in New Hampshire, Vermont, and especially Maine, we may be seeing more of these large, lumbering, carnivores in our neck of the woods sometime soon.

Now if youíll excuse me, Iím going off to have a nap. Iíve been feeling a little sleepy latelyÖ