The tundra can be vibrant with life in summer and hauntingly desolate in winter. The harshness of the Arctic climate, the poverty of its soil, and the exceedingly long and dark winters are incredibly hostile to life. But, as philosopher Spinoza remarked, “Nature abhors a vacuum.” Although the opportunities are few and fraught with hardship, some animal species have managed to adapt to life in the Arctic. Their ability to survive the cold and often marginal food conditions has been honed to the utmost perfection.
Of the world’s 4,600 mammal species, about 40 live in the Arctic, and nearly half of those are sea mammals. The Arctic and Antarctic Seas are astoundingly rich in nutrients, more so than all other seas on earth, and are home to millions of seabirds, seals, and whales–the largest creatures this world has ever known.
There are about 9,600 species of birds in the world, yet in the immensity of the Arctic, only about 100 species breed here. Most are migrants who come north during the short, but food-rich summer, raise their broods and flee south at the approach of winter; fewer than 10 bird species live here year-round. Of the world’s more than 750,000 insect species, less than 1,000 occur in the far north; of the roughly 30,000 species of fish, less than 100 live in the northern seas, lakes and rivers. There are no reptiles that exist in the Arctic, and although several species of toads and frogs inhabit the boreal forest belt, no amphibian ventures north of the treeline.
In the fall, all life in the Arctic prepares itself for the inevitable coming of winter. Compelled by special hormones, migratory birds feed almost incessantly to accumulate the fat reserves that will fuel their long flight south. Ground squirrels, who have nearly doubled their weight since spring, busily stock winter dens with food supplies. Barren ground grizzlies are swathed in fat so thick, it will sustain them through their long winter hibernation until spring. Arctic foxes cache surplus food–lemmings or young birds–to ease winter’s hardship.
Char, the large, far-northern fish who have feasted all summer at sea, return in the fall to the lakes where they will spawn. Historically, Inuit, the indigenous peoples of the Arctic, would spear them and store large quantities of the fat fish as food for winter. The caribou are well provisioned in the fall as well; about one-fifth of their total weight is comprised of fat. Even plants store lipids in their roots and rhizomes for that magic moment nine months later when winter will yield again to spring and instant, rapid growth will be imperative.
Insects can neither flee, like birds, from the Arctic winter, nor shield themselves, like mammals, with thick layers of fat and fur. Instead, they produce within their bodies a glycerol-like antifreeze so efficient, they are able to survive temperatures as low as –70 degrees Fahrenheit. The insects spend winter in suspended animation and resume life nine to ten months later when the warmth of spring awakens them.
As winter approaches, birds become more and more agitated. Increasingly cold temperatures, as well as shortening days and declining food sources, trigger “zugunruhe”–what ornithologists call the nearly febrile restlessness that grips them just prior to migration. Dense groups of knots zigzag into the sky, flashing alternately in red and brown as all birds of the flock turn abruptly in unison. Old squaws gather in large rafts and swim, neatly spaced and aligned, back and forth along the coast. Nervous, twittering flocks of snow buntings drift like snowflakes across the land. Skeins of snow geese wing purposefully south. Each day more birds depart, and the snow and silence once again descend upon the North.
Ptarmigan, ermine, and foxes change color into their winter white, as do the hares of the lower Arctic, which are an earthy brownish-gray in summer. In the far North, where summer lasts barely two months, Arctic hares remain white year-round. They also have some very peculiar habits not shared by their more southerly cousins. In late fall and winter, they gather in large flocks. When alarmed, these hares bolt upright, and as biologist David Gray observed, bounce “up and down on tiptoe while assessing the danger,” then bound away on long hind legs in rapid kangaroo-like leaps.
All animals produce heat by releasing the energy stored in their food, particularly in lipids, proteins, and carbohydrates. The normal body temperature of mammals hovers around 100°F (100.8°F in polar bears, 101.2°F in musk oxen, 98.6°F in humans), and these temperatures are constant and vital. When the air temperature is low enough to sap an animal’s body heat faster than it can be generated, its core temperature is lowered and thus, the animal is put in immediate danger. A naked, hairless man (the least adapted of Arctic animals) exposed to temperatures of –40°F and winds of 30 mph (conditions common in the Arctic) will die in about 15 minutes. The Inuit avoided this fate by dressing in the skins of the Arctic’s superbly cold-adapted creatures.
Animals living in the Arctic have two ways of coping with the cold: 1) They can increase their metabolic rate (their internal heat production) by eating large amounts of food, and 2) They can prevent loss of body heat through insulation. A 70-pound sea otter eats about 15 pounds of sea urchins, mollusks, and fish on a daily basis. Given the chance, a polar bear can devour 100 pounds of high-calorie blubber at one meal. Wolves, after a successful hunt, consume a quarter of their body weight in food. Ptarmigan are forever busy snipping buds and shoots; in order to stay alive through the winter, they require a daily food intake roughly equal to one-fifth of their body weight. But there is obviously a limit as to how much food an animal can consume to stoke its body’s furnace, and for survival in this icy realm, animals rely more upon heat conservation than on heat production. Their insulation–fat, fur, or feathers–effectively shields them from the cold and enables them to live in the arctic environment.