Arctic Dreams, page 11
It is its layer of blubber that causes a polar bear to overheat so easily. The blubber is heaviest on the outside of the back legs and over the buttocks and lower back, where it may be as much as 4.3 inches thick. Lesser amounts are on the upper body, front legs, and neck. Polar bears depend on their blubber for warmth, especially in the water, and for nourishment. During the five months a female is hibernating, giving birth, and nursing her cubs, she lives entirely on her fat reserves. Bears waiting out storms in temporary dens and bears ashore waiting for sea ice to form in the fall do the same. This regimen is such that in southern Hudson Bay denning females may come ashore weighing 750 pounds in early August and emerge from their dens in April weighing only 350 pounds. Similarly, males coming ashore in late summer may lose 30 percent or more of their body weight in the three months that pass before ice forms and they are able to hunt on the sea ice again.
During the summer, especially on the tundra of the Hudson Bay coast, bears dig summer sleeping pits to get out of direct sunlight, sometimes digging down to the layer of permafrost to cool off. When trying to sleep in warm weather, they often roll on their backs in order to expose their bellies and feet. In cold weather they hug their back legs to their stomachs with their forelegs, curling tight to bury their heads in their chests, where they breathe warm air with their backs against the wind.
Øritsland’s experimental findings have a certain attractiveness because they simplify and provide numbers. To watch polar bears in the wild, however, is to marvel at the intricacy of their physiology and behavior. The animals alternately seek shelter or exposure, sleep and travel, hunt down certain foods, and mate and hibernate. The interplay here among rest, exertion, and nutrition that carries them comfortably through life is something that cannot be broken down into pieces. Like the skater’s long, graceful arc, it is a statement about life, the full exercise of which is beautiful.
The bears that are successful, that respond with insight to new circumstances, that do the right thing at the right time, season after season, may live to be thirty. Beyond learning how to secure food, the most intriguing aspects of their behavior are the steps female bears take to ensure that there will be more bears.
Before she dens, usually in late October or early November, a female bear must put on a heavy layer of fat to sustain herself (and her cubs) until she emerges to hunt again in the spring. If the weather doesn’t turn stormy and food is abundant, a female might den late. If little food is available, she may decide not to den at all that year. In the face of early storms that keep her from feeding, she may make a temporary den, wait out the weather, and then decide what to do. Polar bears conceive during the female’s three-week estrus in April and May, but the fertilized eggs do not implant in the uterine wall until much later—some speculate at the moment the female commits herself to a long denning period, which only females carrying fertilized eggs do.
Bears are as particular about the type of snow they select for a maternity den as Eskimos are in constructing an iglu, and the two structures have many features in common. The female usually chooses a site where snowdrifts develop in early autumn, often close to the top of the leeward side of a ridge. Midwinter storms are not likely to expose a den built there, nor is the den likely to be buried in an avalanche. The variety of structures denning females build is great, but they share a certain architecture: an entrance tunnel 5 to 10 feet long and 24 to 28 inches wide and high; a small room at the end of the upward-sloping tunnel, just big enough for the bear to turn around in; and a ventilation hole.
By designing for the flow of air and controlling the thickness of snow, an excellent insulator, a female can keep fresh air moving through her den all winter and maintain the temperature at about 32°F, no matter how cold it gets outside. She does this by radiating a small amount of heat, about as much as a 200-watt bulb, and by trapping that heat in the den chamber with a sloping entrance tunnel and an air dike, or sill, where the tunnel enters the den. She also adjusts the thickness of the roof. (Eskimos put the same techniques to use.)
The female is not actually hibernating during the winter. Her heartbeat and rate of respiration are greatly reduced, but her temperature falls only very slightly. She can awaken and become alert in moments. If her den gets too warm, ice will form on the walls, cooling the chamber and inhibiting the exchange of carbon dioxide and oxygen through the snow walls. The bear may then scrape off the ice and adjust the ventilation, or dig a new chamber adjacent to the old one. Jørn Thomassen, who has watched denning bears in Svalbard for several years, speculates that some females are more successful than others at designing and maintaining these structures, and that older bears, learning from their own mistakes, subsequently build dens where the exchange of gases, the conservation of heat, and, later, the expansion of the den to allow the cubs to exercise before they emerge, are accomplished with more economy.
Dens are very clean. By metabolizing fat instead of protein, the female produces very little body waste. Except for a mouthful of snow now and again, she also draws all the water she needs from her fat reserves.
Cubs, usually two but sometimes one or three, and very rarely four, are born sometime in December or early January. They are blind, deaf, poorly insulated, and unable to walk or smell. In their first weeks they are dependent on three things for survival: the protection of the den, the warm crevices of their mother’s body, and her rich milk. (Polar bear milk has the consistency of cream. Those who have tasted it say it tastes like cod liver oil and smells of seals or fish. It is richer than whale milk and higher in protein than seal milk.) Again, it is only with the protection of a well-made den that a female can conserve and direct her metabolism to produce the heat and milk that her cubs need.
The cubs are so small at birth, barely a pound, that the female can hide one in the rolled toes of her front paw. At about twenty-four days they can hear, and a week later they are able to see. It is several more weeks before they can walk and smell. By late March or early April the cubs weigh about 25 pounds, and the female, depending on the weather and the cubs’ condition, breaks out of her den. For the first days she might just sit drowsily in the sun at the den entrance. Or roll in the snow to revive her coat. Or nose about in a desultory way, looking for grasses and lichens to nibble.
A well-placed den entrance will be protected from the wind and directed in some measure to the south and west to take advantage of the sun’s afternoon warmth. Cubs venture forth onto this sheltered sun porch a few days after their mother and for the next few weeks do not travel far at all. Their mother often nurses them here in a sitting position in the sunshine, with her back against a snowbank. The cubs lie on her belly. While they nurse she may put her head back and stare at the sky, or roll her head slowly from side to side, or rock her cubs gently in the cradle of her forelegs.
These first few weeks are a critical time for all three animals. The female balances her desire to leave in order to hunt to feed herself against an investment in the cubs’ learning, exercise, and preparation for travel. For most bears the sea is no more than a day away. For others, like those denning on the southern coast of Hudson Bay, the journey is much longer and requires making temporary dens along the way.
Rasmus Hansson and Jørn Thomassen, who have watched more bears emerge from their dens than probably anyone else, studied bears for several years at a traditional denning area called Bogen Valley, in Svalbard. Most of the bears there den in a long line just below the ridge of Retzius Mountain. (In spite of this density it is very rare to see two families outside their dens at the same time. How the females manage periods of exercise so as not to interfere with each other is not known.)
Since portions of the southwest face of Retzius Mountain slope at an angle of 70°, the first problem cubs face there is getting down to the floor of Bogen Valley. They learn to imitate their mothers, who slide down rump first, looking over their shoulders and braking with their claws; or on their sides, leading with all four feet; or headfirst on their bellies. Mothers at the bottom catch cubs veering out of control.
In those first few days outside together, say Hansson and Thomassen, the females tend to rest while the cubs exercise vigorously. The cubs pick up blocks of ice or snow, which they then throw and chase or wrestle with violently, biting and chewing like cats. Cubs also stand up to swat at each other and roll over thrashing and neck-biting in the snow. In analyzing the cubs’ behavior, the two Norwegian scientists concluded that the cubs were developing in three areas: strength and coordination; social habits and communication skills, which would permit the female and her cubs to live and hunt together efficiently during the next two years; and fighting techniques. In the future the latter would serve males in their battles with each other during the breeding season, and females in the defense of their own cubs. (Male bears, according to some researchers, will try to kill any cub they encounter, especially if the female offers a weak defense.)
When cubs reach some threshold level of strength and coordination, when they are able to walk well and are responsive to their mother’s instructions to “stay” and “come,” the bears depart from the den. The time of all three having to live solely on the stored fat of the female is nearly over.
The Polar Eskimos of northwest Greenland call the polar bear pisugtooq, the great wanderer. On the basis of mark-and-recapture studies and radio-tracking information, scientists have determined that individual bears wander largely within a local area; but some, indeed, are long-distance travelers. A polar bear tagged in Svalbard, for example, showed up a year later near Nanortalik, Greenland, 2000 miles to the southwest. Another bear, a female, traveled a straight-line distance of 205 miles in two days. Polar bears have also been found far afield in unlikely places, at the crest of Mount Newton in Svalbard, for example, 6600 feet above sea level, or 30 miles inland on the Greenland ice cap. An American crew on the ice island Alpha saw a female and her cub at 84°N in December 1957. (She had become entangled in runway lighting, which she tore out moments before a plane attempted a landing.) A Russian ice-island crew spotted a female and her cubs a little more than a hundred miles from the Pole in the summer of 1937.
Because we think of polar bears as northern animals, and of “the North” as an area that doesn’t extend very far south, it is somewhat surprising to discover that bears den at only 53°N, on Akimiski Island at the southern end of Hudson Bay. Or that bears still turn up occasionally on the east coast of Newfoundland as far south as Saint John’s. Some stories of their wandering have an esoteric perseverance and loneliness about them. In 1938, for example, an aging female was shot far inland in the province of Quebec, near Peribonka on Lac Saint-Jean. She had apparently ascended the Saguenay River from the Gulf of Saint Lawrence and was headed for James Bay, some 360 miles farther north.
Once, looking up from the sea ice at the coastal cliffs of Devon Island, Ray Schweinsburg, a Canadian polar bear biologist, said to me, “I used to think the land would stop them. But I think they can cross nearly any terrain. The only thing that stops them is a place where there is no food.”
The bear is a great wanderer not solely because it travels far, but because it travels with curiosity, and tirelessly. The Eskimo hunters in Greenland mean that it covers the ground successfully and intelligently when they pronounce the word pisugtooq.
Eskimos, long-time, keen observers of the polar bear, have advanced other thoughts about polar bears that science has treated with skepticism, and in some quarters with cynical disdain. Eskimos widely assert, for example, that most polar bears are left-pawed, that if one must leap in desperation from a charging bear it should always be to the bear’s right.6 Eskimos have also asserted that polar bears push blocks of ice ahead of them as shields when they are stalking seals; that a wounded bear will staunch the flow of its blood with snow; that they will hurl ice and rocks at walrus to wound and distract them, hoping to snatch an unprotected calf; and that females use anal plugs when they den.
Refuting any of these things is a complicated business. It becomes not only a denial of the integrity of the person telling the story, but a denial of the resourcefulness of the polar bear. Too, because of poor translations, you might end up refuting something that was never meant. The best field biologists, with a fundamental grasp of the animal’s behavior, take the attitude that these things could happen, though they themselves have not seen them. The anthropologist Richard Nelson has offered succinct advice on this issue. “Eskimos,” he writes, “are highly reliable observers of animal behavior, and many of their least believable statements have been proved to me by personal observation.” Some scientists strongly resisted the notion that bears might use tools until a Canadian biologist found evidence in 1972, on the north coast of Devon Island, that a female with two cubs had smashed in the roof of a ringed-seal lair with a 45-pound piece of ice. Scientists have also found that bears intentionally stalk small prey like lemmings, which Eskimos have long claimed they do. And that a polar bear will hunt sea ducks by coming up underneath a flock of them in the water like a killer whale.
One of the most persistent of bear legends—that they cover their dark noses with a paw or a piece of snow when they are stalking a seal—may have originated with Eskimos, but the thought has the flavor of invention about it. At a distance of 1000 yards, the argument goes, you can barely distinguish a polar bear on the sea ice, but you can clearly see its black nose. How could a seal not notice it? It’s possible that it does—and that that is exactly what the bear intends. To a seal, a polar bear approaching in a straight line over flat ice, its lowered forequarters sliding along ahead of its hindquarters, would show very little body movement—the pushing motion of the rear legs does not break the outline of the hips. If the seal focuses on the dark nose, the bear’s shape falls into vague relief against the surrounding ice. And at that distance the nose looks like another seal resting on the ice. Because of an optical phenomenon, the size of the bear’s nose does not begin to fill more of the seal’s image of that part of the sea ice until the bear is almost on top of the seal. And at that point the bear rises and bounds toward it.
It is possible the bear goes down on its forequarters only to keep the horizon from showing up between its legs; but it is also possible it wants its dark nose down there on the ice where it looks like a seal. Without direct evidence, without setting up an experiment, one can only speculate.
The desire to verify conjecture, to witness spontaneous, unstructured events in the wild, is of course very sharp among field biologists. Nothing—no laboratory result or field-camp speculation—can replace the rich, complex texture, the credibility, of something that takes place “out there.” And scientists working in the field know that what they see in the field always has the potential to contradict what they have read or been told.7 One-time events, like seeing a polar bear stalk and kill a seal in open water (some biologists doubted this ever occurred, until one of them, Donald Furnell, and an Eskimo companion, David Oolooyuk, saw a bear do so in 1978), may be of no statistical importance. It may not be possible, in other words, to generalize about all bears from these incidents. But such events emphasize the resourcefulness of the individual bear and the range of capability in the species; or they may reveal an unusual technique widespread only in a certain population. These events underscore something critical in the biology of large predators: the range of capability in the species. No matter how long you watch, you will not see all it can do.
Once, in a helicopter flying along Barrow Strait, Ray Schweinsburg and I saw a lone bear headed south across the ice. “I’d like to follow him,” Schweinsburg shouted over the engine noise. “I’d like to go down there and just follow him.” And he rolled his eyes and smiled at the impossibility of it.
I looked out the window, at the hundreds of square miles of ice that lay ahead of the bear. Even if it were possible to follow, I thought, how well could we put together what we saw? What would we miss out there? I remembered again the desert writing of Wilfred Thesiger, wandering in the Empty Quarter with his Bedouin companions. The Arctic reminds one of the desert not only because of the lack of moisture and the barren topography, but because it puts a like strain on human life. It favors tough and practical people, people aware of the vaguest flutter of life in an environment that seems featureless and interminable to the untrained eye. People with a predator’s alertness for minutiae, for revealing detail. The loss of “a native eye” among civilized cultures has been commented on by people as diverse as Vladimir Arseniev, writing about the Manchurian native Dersu Uzala, and Laurens van der Post, writing about Kalahari Desert people.
It not only takes a long time of watching the animal before you can say what it is doing; it takes a long time to learn how to watch. This point is raised, deferentially but repeatedly, in encounters with Eskimos. They are uneasy, they manage to say, about the irrevocability of decisions made by people who are not sensually perceptive, not discriminating in these northern landscapes, not enthusiastic about long-term observations. When I hear these points made, my instinct is to nod yes; but it always causes me to reflect on something else—how dependent we are on Western field biologists to tell us fully and accurately what the animals did while they were there. How we hope they regain some approximation of “the native eye” in their studies.
The bear I was watching disappeared, cut off by the door frame of the helicopter.
To follow a bear, or simply follow in its tracks, is to “reeeally learn something,” as the Eskimos say, smiling. Not only about where a bear went, but how it dealt with what happened along the way. A set of tracks might show where a bear had leaped into the air and come down headed in another direction—and you would look around for evidence of what surprised it. The trail of a cub alongside its mother disappears where it has crawled up onto its mother’s back for a ride on a cold day. Bear tracks on the sea ice might follow the line of a pressure ridge (where seal lairs are likely to be) at a distance of 100 feet or so on the downwind side. Fresh tracks turning into a fiord might make no sense until you saw a bird rookery, beneath which the bear had scavenged dead birds. A male’s tracks might cross a female’s and turn to follow. Another set of tracks might turn suddenly and continue in an unerring line, and an aglu, a seal’s breathing hole, would be there at the end, with signs of the bear’s patient waiting. Tracks below a high bluff would show where a bear had hunted on a July morning, out of the sun.
