Column: How critters adapt to survive a Minnesota winter
It is March in Minnesota once again. Springtime will soon be upon us, though meteorological spring is already here in the northland. And with all things considered — snow depth, temperature, and more snow and cold in the forecast — we could be looking at a very late spring this year.
While we humans are comfortable inside our warmly heated homes, one need only to look outside and imagine what it must be like to live each day in the elements, as do a host of wildlife species that call Minnesota their year 'round home, to appreciate just how good we have it.
Rightfully so, we associate snow with cold, yet, ironically, it's the snow itself that contributes to the survival of many species of wildlife.
Every year by late autumn, the pelage of snowshoe hares and jackrabbits turns 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. As most people know that are familiar with ruffed grouse and voles, these two species take advantage of this fact by seeking shelter 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. This winter's abundant snowfall events are a boon to ruffed grouse. The soft snow helps these birds survive.
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.
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. Black bears sleep, too, although their mode of hibernation is considered less intensive than that of hibernating ground squirrels.
Indeed, surviving northern Minnesota winters boils down to adaptation and endurance. Species of wildlife accomplish amazing and seemingly impossible, numerous, and complex ways to survive wintertime — all worthy of our wonderment and appreciation — as we get out and enjoy the great outdoors.