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Wednesday, 18 October 2006 00:00

Cold weather and deep sleepers

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This past weekend’s sudden drop in overnight temperatures into the high 20s (26 degrees and 28 degrees Fahrenheit, respectively, at our place near Bryson City) was unprecedented in our experience. That is, during the 33 years my wife, Elizabeth, and I have resided in Western North Carolina, we have never known temperatures to drop from the low 40s into the high 20s without at least a few nights in the 30s in between.

 

This sudden change also caught the snakes and other wild critters on our place by surprise. Snakes usually start to den up and hibernate for the winter when temperatures reach the mid-30s. But several northern copperheads that reside on our property — obviously unaware that cold weather was on the way — were hunting prey in our garden areas as of mid-day Sunday. Small toads that were themselves caught short by the cold seemed to be what the copperheads were primarily feeding upon.

Biologists classify the normal human method of making it through winter as “resistance.” Like many other animals (deer, many birds, rabbits, squirrels, bobcats, etc.), Elizabeth and I stay where we are in the world and face up to the rigors of the season, resisting its stresses. We hunker down and endure. We have stacked more firewood than ever before, cleaned out the woodstoves, and filled the horse barn to the rafters with bales of hay.

Some folks, of course, copy the birds and migrate south to Florida or some other balmy region, where they simply await the return of spring. But “migration” — the second cold-weather strategy identified by biologists — is a risky business for most animals. The energy reserves of migrant birds flying over water sometimes become exhausted before they reach their destinations. And the demands of migrating overland are even higher, which is why most animals practice either active “resistance” or passive “hibernation.”

That third strategy is perhaps the most intriguing. Most of us know, in general terms, what hibernation is, but even scientists who have studied the process closely for years admit that they don’t fully understand how itoperates. It has been described as a state of winter dormancy in animals that represents a special case of temperature regulation whereby an animal lowers its “thermostat” so as to maintain lower than normal respiration, heart rate, and body temperature to save energy while maintaining those body functions essential for survival.

Throughout the world, there are various mammals, birds, reptiles, amphibians, and insects that practice hibernation in one form or another. In our region, toads dig several feet down into soft soil, while frogs and turtles burrow into underwater mud. Snakes congregate in communal rock dens. Copperheads, timber rattlers, and black snakes often spend the winter together, sometimes traveling a considerable distance to do so in the same den year after year.

Birds that over-winter in our region mostly utilize the resistance method, but at least one species has developed a technique that might be called “overnight hibernation.” The black-capped chickadee, which nests in the higher elevations of the southern mountains and comes down to the lower elevations during winter, reduces its rate of heat loss at night by deliberately ceasing to shiver. This causes its body temperature to drop until a level of hypothermia is reached. On a cold night, these tiny birds can allow their internal temperatures to drop up to 12 degrees, resulting in a large overnight energy savings as they burn less fat than if they were more actively resisting the environment.

Chipmunks, woodchucks, jumping mice, black bears, and bats are the mammals in our region that regularly practice hibernation in one form or another. When there is a permanent winter cover of snow, raccoons and skunks also become dormant. In the strictest sense, however, only the woodchuck, jumping mouse, and bat are true hibernators. These three must have time to warm up before they can wake up. This slow arousal process is the mark of a true hibernator.

The woodchuck is our region’s most remarkable hibernator. In preparation for their winter snooze, they tunnel burrows that may be thirty feet long with five or more entranceways. Bedroom chambers lined with grass are created above the main tunnel so as to protect them from flooding. Before winter, they eat up to a pound and a half of vegetation daily, depositing a three-fourths-inch layer of fat under their hides.

Activity is reduced as cool weather approaches, so that by early November most woodchucks will have disappeared into their underground hibernacula, not to reappear until late February or early March. Yes, I know, Feb. 2 is Groundhog Day, when this critter supposedly looks for its shadow to determine whether winter will be shortened or extended; but that’s just another pleasant myth.

During the woodchuck’s four-month period of dormancy, its body temperature falls from almost 97 degrees to less than 40 degrees. The animal breathes only once every six minutes, while its heartbeat drops from over 100 beats per minute to just four per minute .... the sort of truly deep sleep that has been appropriately described as “the little death.”

George Ellison wrote the biographical introductions for the reissues of two Appalachian classics: Horace Kephart’s Our Southern Highlanders and James Mooney’s History, Myths, and Sacred Formulas of the Cherokees. In June 2005, a selection of his Back Then columns was published by The History Press in Charleston as Mountain Passages: Natural and Cultural History of Western North Carolina and the Great Smoky Mountains. Readers can contact him at P.O. Box 1262, Bryson City, N.C., 28713, or at This email address is being protected from spambots. You need JavaScript enabled to view it. .

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