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Blane Klemek: How animals survive the chilly winter months

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Meteorological winter can be defined as “. . . a three month period that runs from Dec. 1 to the end of February.” And while the calendar still shows that we’re in the final days of fall, winter, for all intents and purposes, is definitely upon us. One needs only to look outdoors to come to that conclusion.

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But take heart Minnesotans, winter solstice will be here on Dec. 21 and from that day forward the days will gradually lengthen and become warmer. Even so, winter appears to be here for the long haul and we, as well as the resident wildlife we share space with, are adapting, coping and are surviving.

I often wonder how species of wildlife survive the harsh extremes of temperate climates such as Minnesota. And I wondered again after I finished plowing our early December snow with my old H Farmall tractor. The snow was light and fluffy and would not support the weight of chickadee much less that of a cottontail rabbit or deer. How do the latter two animals manage to get around in such conditions?

In due time, following a few “freeze-thaw” events that will undoubtedly occur from time to time, the snowpack will harden and, at least for some animals, getting around will become a little easier. But in the meantime animals such as jackrabbits, hares, and cottontails, as well as deer, squirrels, bobcats, fox, coyotes and wolves, will adjust their daily and nightly patterns as they begin to establish trails in the snow and search for food that has suddenly become more difficult to procure.  

Ironically, it’s the snow itself that contributes to the survival of many species of wildlife. Every year by late autumn snowshoe hares and jackrabbits turn snow white in color. The pelage change is an adaptation that enables the animals to blend in to their environment, thus avoiding easy detection by predators. Even some predatory mammals have evolved this ability to turn from brown to white. All species of weasels in the northern latitudes turn mostly white by winter and become nearly invisible as they hunt for prey. The arctic fox is another.

Snow insulates the ground, plants and animals extremely well from the cold and wind. Ruffed grouse and voles take advantage of this fact by seeking shelter and living beneath the snow. In the case of a ruffed grouse, burrows are created when the bird flies headfirst into the snow to escape frigid nights and inclement weather. Not only does this technique enable grouse to survive bitterly cold temperatures, it has the added benefit as a near-perfect hiding spot from predators such as bobcats and northern goshawks.

Voles, on the other hand, spend pretty much the entire winter beneath the snow. At that interface where snow meets earth, voles are going about their lives as active as ever. Snow also serves as excellent protection for plants. Ground hugging herbaceous plants and small trees and shrubs are protected from cold, wind, and sun by a blanket of snow.

Of course, some creatures choose to migrate. As food supplies dwindle, most species of birds that we observe in the spring, summer, and fall travel to warmer climates. However, many critters remain behind — and for those that do stay and remain active throughout the winter, food and its availability become critically important.

White-tailed deer, for instance, consume an abundance of high-protein, nutritious foods before the onset of winter in order to add fat to their bodies. Stored fat enables deer and many other animals to survive the lean times by keeping them warm and alive when food is scarce. Additionally, metabolic rates of deer decrease in the winter to effectively reduce the energetic costs of maintaining life. And it doesn’t hurt either that a thick winter coat of hair is grown every year well ahead of winter’s arrival.   

To survive cold winter nights, many species of birds enter states of “mini-hibernation.” Called torpor, this physiological adaptation reduces a bird’s need for food by decreasing their metabolism through the reduction of heart rates and body temperatures, which in turn allows them to survive the long hours of nighttime while eliminating the need to feed. Behavioral adaptations are also employed. Chickadees and other birds are known to enter tree cavities and bird houses, sometimes in groups, to avoid the cold and to stay warm by sharing body heat by “huddling.”

Many species of mammals are completely inactive during the winter for several months at a time to a few days or weeks such as eastern chipmunks, woodchucks, and thirteen-lined ground squirrels. These animals enter states of true hibernation. This “deep sleep” in which body temperatures and heart rates decreases to — in some cases — a point of almost no return, is critical to their survival. Furthermore, just as in those animals that stay active, stored body fat (and in some cases, stored food) is essential as well.           

Reptiles, amphibians, and insects are unique in many ways from warm-blooded organisms. Some snakes spend the winter in underground dens and form entwined “snake balls” with other snakes to insulate themselves from the cold, wood frogs actually produce a natural anti-freeze to keep their body’s cells from totally freezing, and several species of insects survive the winter in larval forms by burrowing underground or by congregating together to form large nests.

Indeed, to survive — or escape-a Minnesota winter it all boils down to a matter of adaptation and endurance. From those species that migrate to warmer climates to species that cope by hibernating, the variety of ways that wildlife survive wintertime are as numerous as they are fascinating as we get out and enjoy the great outdoors.

BLANE KLEMEK is a Minnesota DNR wildlife manager. He can be reached at bklemek@ yahoo.com

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