Animals have tools to survive winter
While standing outdoors on a cold winter day or night bundled from head to toe in your warmest winter wardrobe, have you ever wondered how resident wildlife survive?
How is it that birds as diminutive and seemingly fragile as black-capped chickadees manage to show up daily at your feeders throughout the winter, no worse for the wear?
Indeed, while Minnesota's year-round resident wildlife are masters of survival, Mother Nature has equipped them all with the necessary tools to do so.
Ruffed grouse, for example, actually fare best during the winter, when snow is deep enough and of the right consistency for burrowing into. "Ruffies" dive headfirst into soft snow to escape the coldest days and nights. These "snow roosts" can be 50 degrees warmer than the ambient outside air temperature!
Ruffed grouse remain snug and warm inside their snow caves. Snow is ideal insulation that helps grouse conserve valuable energy throughout the long winter months. Not only do these snow roosts protect them from bitter cold temperatures, wind, blizzards and the like, snow roosting helps keep them hidden from predators, too.
Some species of mammals turn a different color seasonally in order to escape detection from predators and prey alike. Except for the tips of snowshoe hares' and white-tailed jackrabbits' ears, as well as the tips of weasels' tails, which are black, these species of mammals' fur coats are snow-white in the winter. Conversely, their pelage changes to brown in the spring, and by summer their brown coats blend in with their environment as effectively as do their white coats in the winter landscape.
White-tailed deer are also survivalists. Deer respond to the challenges of winter both physiologically and behaviorally. Nature has provided them with the ability to decrease their metabolism, and so deer require less food to eat in order to survive during times when food is normally scarce.
Additionally, a deer's dense coat of long hollow, air-filled gray hairs replaces its red-colored, shorthaired summer coat. It insulates against the cold so well that falling snow can pile up on a on a deer's back without it melting because very little body heat escapes through the thick winter coat. And being an intelligent creature, a deer will also use available cover to escape cold winds and temperatures. Deer actively seek out coniferous woods, cedar swamps and other wooded shelter when inclement weather sets in.
Some of Minnesota's wildlife escape to warmer climates before winter approaches. Most notably, of course, are the many species of waterfowl and neotropical migrants. Migration is what works best for them, as well as for some mammals, such as bats. Meanwhile, other critters manage Minnesota winters by simply sleeping through it.
Black bears enter a state of torpor in late fall and emerge from their dens by March or April. They survive several months without eating by living off of the enormous amounts of fat reserves their bodies accumulated over the course of spring, summer and fall eating binges. Other mammals, such as species of ground squirrels like woodchucks and chipmunks, enter into true hibernation. These mammals' heart rates and body temperatures plummet to such extremes that life itself is barely hanging on. Whereas black bears more or less slumber through the winter, ground squirrels are nearly comatose.
Still, other small mammals, such as shrews, moles, pocket gophers, deer mice and voles, stay active throughout the winter in underground systems of tunnels, underneath the snow or inside other forms of natural and man-made shelters.
On the far, far side of the survival spectrum are species of wildlife that defy logic. The wood frog is an astonishing example.
After the wood frog has crawled underneath a log, a pile of forest debris, or whatever else it can find in the woodland, the amphibian undergoes a bewildering physiological feat: it freezes -- well, almost.
A wood frog's body produces a natural anti-freeze (glycerol) to keep its cells from freezing solid. In the spring when the frogs "thaw out" they are the first anurans to emerge, breed and lay eggs.
And those chickadees? Somewhere between black bear and ground squirrel survival strategies, you can find the chickadee doing what they do best. These birds are extremely energetic and active throughout most winter days as they forage for high-energy foods and cache as much as they can for later. However, it's at nighttime that these tiny titans rise to the challenge.
During frigid nights, chickadees are able to enter a mini-hibernation by decreasing their metabolic rates just enough so their energetic costs of survival are not so high. After all, staying warm would require input in the form of food -- something they can only acquire during daylight hours.
So, through chickadees' nighttime torpor, along with seeking shelter inside tree cavities or huddling together with other chickadees to capture their neighbors' body heat, chickadees can cheat on Old Man Winter.
Winter is often a time of tremendous hardship for Minnesota wildlife. Aside from food, fat reserves and shelter, survival also depends on behavioral and physiological strategies and mechanisms.
Yet despite any given creature's intense will to survive, winter is also when life sometimes comes to an end. Nonetheless, the tenacity of all creatures great and small should never cease to amaze us as we get out and enjoy the great outdoors.
Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at firstname.lastname@example.org.