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