This winter has been a mix of unseasonably warm days followed by bone chilling temperatures. If you have had trouble deciding whether to wear your raincoat or down jacket before heading outside, imagine what it must be like for wild animals.
Some creatures are oblivious to the cold and wind because they are hibernating underground or in some sheltered space. Their bodies have shut down and entered a period of suspended existence, just short of death. In our area only the woodchuck, some bat species, meadow and woodland jumping mice and black bear are considered to be true hibernators. What they have in common is that their prime food becomes scarce or non-existent in winter. This is the case with the woodchuck that eats herbaceous plants and bats who feed on insects.
True hibernators go through a dramatic metabolic change. During hibernation they do not eat, drink, defecate or urinate. Their heart and breathing rates drop drastically. The woodchuck's heart rate declines from 100 beats per minute in summer to about 15 during the winter. In most cases hibernators also have a very low body temperature. Black bears are one exception to this rule, making their classification somewhat controversial. Their heart and breathing rates decline during the winter, but the bears' core body temperature only drops a few degrees from normal. As the definition of true hibernation has broadened, black bears have been added to the list of hibernators.
Though bear behavior may be hard to define, several species of mammals can definitely be labeled as dormant or "sleepers." Raccoons, skunks, opossums, and chipmunks sleep for extended periods without experiencing a major metabolic change. Food storage is a key adaptation for them. Chipmunks cache their food in burrows where they can access it during the winter without going outside.
The strategy employed by raccoons and skunks is to add body fat during the fall. This acts as insulation but is also a source of energy when they are sleeping for weeks at a time. When the weather is mild they emerge in search of food to augment what they have stored. During a recent warm spell my yard was crisscrossed with skunk tracks heading for an easy buffet at the compost pile. But with the return of colder weather, fresh tracks will be left only by the truly active creatures.
Mammals which stay active throughout the season make up the majority of our native populations. Squirrels, and most of the rodents (including beaver and porcupine), rabbits and hares, coyotes and foxes, bobcats and lynx, all of the weasels (except the skunk), deer and moose have other adaptations which help them survive the cold and reduced food availability.
Deer and moose change their diet from herbaceous to woody plants. Beavers store food under water near their lodge. Squirrels make stashes of seeds and retrieve them when other food becomes harder to find.
Many of these creatures also put on a winter coat. Under-fur will thicken, creating cozy protection from the winter cold. The outer layer of guard hairs are usually hollow, able to trap and hold the body heat generated by the animal and block the outside cold from penetrating. Snow may build up on the back of deer without melting, because their fur creates a layer of air between their warm bodies and the snow. In the case of snowshoe hare, long- and short-tailed weasel or ermine, their winter fur also provides camouflage as they turn white to blend in with snow.
Behavioral changes may also include congregating together to share warmth or reduce energy needed to move around. Raccoons will den together, deer congregate in "yards" under evergreen trees where the snow is not as deep, squirrels gather in tree cavities or leaf nests and beaver families stay together in their underwater lodges.
It is a marvel to observe how local wildlife is adapted to the challenges of winter. Why not bundle up with your own strategies for keeping warm and go in search of some of these intrepid neighbors? There are plenty of animals who aren't hibernating or hunkered down, and winter is a wonderful time to discover their tracks and signs.