Moose were really designed for winter. Their thick coats of hollow-shafted hair keep them warm at 40 below zero—by the time the temperature reaches 20 degrees above, they’re usually looking for shade. It’s true, they can’t reach their summer diet of aquatic plants, but they do just fine on 40 pounds a day of stems and twigs from willow birch and fir. If you’re a moose, summer’s the problem. You’ve got to go stand in water half the time just to stay cool.
For most of the rest of us, however, coping with cold—with the defining fact of winter—demands a certain amount of hard work and ingenuity. The natural world has come up with a variety of approaches, many of which are enough to make you glad for Patagonia and North Face.
Consider the spruce grouse, for instance—they sometimes fly headfirst into snow banks, burrowing in to take advantage of the insulation the drifts provide. Though air temperature may be bitter cold—zero, say, by the time you get ten inches down in the snow, the air pockets formed by snow crystals mean that it’s a proper 32 degrees. The short days of fall also trigger a hormonal change in spruce grouse, causing their toes to grow new scales—before long their feet have twice the surface area, letting them stroll across the snow with ease. Not only that, but to cope with the fact that it must live on pine needles all winter instead of its summer diet of insects, the grouse doubles the size of its ceca, a pair of sacs between its large and small intestine that is filled with bacteria to help it digest all that roughage.
Plenty of animals-weasel, hare, ptarmigan, Arctic fox-turn white when winter comes. This helps camouflage them, of course. But anyone who’s ever rented a car in Hawaii knows that reflective white is cooler—so how do they stay warm? As it turns out, white helps here, too. White isn’t actually a color of fur; instead, it’s the absence of pigment. The cells in hair and feather that would otherwise hold the color are filled with air instead, and that air means a cozy layer of insulation.
For many other animals, of course, a cozy layer of fat does the trick. Bears hibernate, which means they need to produce much less energy all winter. But they still lose a third of their body weight in the course of the winter, as the fat—as much as 150 pounds that they added by gorging on berries and nuts in the fall—slowly but inexorably burns away. Raccoons go them one better, losing half their body weight as they hole up for the winter.
If you want to see the whole bag of tricks, consider the ultimate winter animal, the polar bear. He’s got that unpigmented white hair. Beneath it he’s got black skin to soak up the sun. Beneath that he’s got four inches of fat. And beneath that he’s got attitude. Which may actually count for something, at least with human beings. We were about as badly designed as possible for life in the cold. Not much hair, we don’t hibernate, and only in the age of super-sizing have we learned to put on a truly impressive layer of body fat. That’s because we grew up elsewhere—on the African savanna where, as biologist Bernd Heinrich explained, almost all our physiology evolved to help us shed heat when we were chasing prey for hours at a time. We have zillions of sweat glands, for instance, and even our upright posture minimizes the amount of solar energy we absorb. It took fire, and clothes, to let us stray very far north—anatomically we remain citizens of the tropics.
When the world around you turns cold, you have to defend your core temperature in one of two ways—save the heat you already have, and make more. Since the blood in your body constantly circulates, it’s easy for it to drain heat into cold air or cold water. To keep that from happening, arterioles—blood vessels with muscles in their walls—close down peripheral veins and arteries. Your fingers and toes get cold—and eventually your skin turns pallid, because very little blood is running through it. You don’t sweat when you’re cold, a smart adaptation, since water is many times more efficient than air at conducting heat away from the body. And you do start to shiver, which is in effect an involuntary form of exercise, your body doing calisthenics for you.
If you spend a lot of time in the cold, your body may begin to adapt. Literature is full of mountain climbers taking ice baths for weeks before their expeditions, and some long distance swimmers seem to accumulate more body fat. There are also stories about psychological adaptation: Laurence Irving, a professor of zoo physiology at the University of Alaska, once noticed a pair of students who, for religious reasons, walked around the Fairbanks campus barefoot, even in winter. In his book "Arctic Life of Birds and Mammals, Including Man," Irving describes wiring the toes and fingers of the two students as they sat in a 32 degree room for an hour in light clothing. Although his control sample, an Air Force pilot, had to be excused from the test after half an hour because he "was shivering so violently" Irving feared he would "shake himself apart," the two students didn’t even start shivering until the hour was almost past, and the thermometers on their digits showed that they had dramatic cycles of cooling and warming—every time their fingers and toes dropped to about fifty degrees, the students reported feeling a tingling, and then their extremities heated back up to almost 70 degrees.
Of course, to generate body heat you could also ski uphill for a quarter mile. That’s certainly easier than trying to grow hair like a moose.
