The Great White Bear

by Kieran Mulvaney

  But if modern polar bears are smaller than their predecessors, they are still the largest bear species in the world. The largest male weighed in Hudson Bay was a thirteen-year-old that tipped the scales at almost 1,450 pounds; the average weight for mature male bears in that population is approximately 1,100 pounds. Steven Amstrup observes that the heaviest bear he and his colleagues have weighed in the Beaufort Sea area of Alaska was roughly 1,350 pounds but that some tranquilized animals were so enormous that they could not be lifted up with a weighing tripod, or even by helicopter. Doug DeMaster and Ian Stirling have estimated that some weigh as much as 1,760 pounds. Females are significantly smaller, and their maximum weights rarely exceed 880 pounds even when they are at their most obese, when they have gorged following mating and prior to denning.

  A mature male may measure over nine feet from the tip of his nose to his stubby tail, stand five and a half feet at the shoulder when on all fours, and reach thirteen feet into the air when standing on his hind legs. Polar bears are not only the largest bears in the world today, they are very nearly the largest that have ever existed; only their ancient ancestors and the extinct giant short-faced bear were larger.

  Size, however, isn't everything. There is more to being a polar bear than being big.

  ***

  It all begins with the head.

  If you had never before seen a polar bear, never even knew that such a thing existed, but were nonetheless familiar with other things ursid, from a panda bear to a teddy bear, Yogi Bear to Gentle Ben, the moment you saw the face of a polar bear you would almost certainly know instinctively and immediately what type of animal it was. It is unmistakably... bearlike, with its rounded ears and furry muzzle. But compare the face of a polar bear to that of a grizzly and one difference is immediately apparent: the latter's seems flatter and wider, while the former's tapers into more of what might be called a Roman nose. The largest brown bear skulls are larger than the largest polar bear skulls; although they are in fact only marginally wider in relation to length than those of polar bears, they are also higher, creating more of a "dish-faced" impression than the more elongated visage of a polar bear. The more streamlined silhouette is accentuated by the neck, which in a polar bear is relatively long and slender, an adaptation that, in combination with the narrower skull, enables polar bears to succeed in hunting prey that would be beyond the reach of their evolutionary cousins.

  "If a grizzly sticks its head in a seal hole," points out the San Diego Zoo's JoAnne Simerson, who has spent many years studying polar bears in captivity and the wild, "then it isn't going to be able to pull it back out."

  And when a polar bear seizes a seal, the weapons it contains inside that elongated skull allow it to dispatch and dissect it with consummate efficiency.

  Its forty-two teeth are significantly different in size, shape, and composition from those in a brown bear's jaw, and they are weighted far more heavily toward grabbing and holding prey and shearing meat. For example, the first premolars, the teeth immediately behind the pointed canines, are vestigial, effectively creating a gap between the canines and the molars that allows the former to penetrate deeply into seals and other prey without hindrance from adjacent cheek teeth.

  The ears, too, are different from those of a brown bear. A grizzly's ears may not be its most prominent feature, but they are significantly larger than those of its nearest relative (while those of a sloth bear appear positively elephantine in comparison). The smaller the ears' surface area, the lower the amount of heat lost through them; and while losing heat is an occupational hazard of Arctic life, it is a danger to which a polar bear is tremendously well equipped to respond.

  Any energy-conscious homeowner will agree that a sign of good attic insulation is a roof on which snow does not melt in winter. So it is with polar bears, the still-frozen snowflakes on their fur evidence that even as they maintain their core body temperature, which is almost identical to that of humans, the tips of their hairs may be as much as 75 degrees cooler.

  By way of illustration of the effectiveness of polar bear insulation, Ian Stirling tells a tale of a fellow researcher who wondered if infrared photography could be used to detect polar bears on the ice, given that all warm bodies emit infrared radiation.

  "To test the idea, he found a bear and took some pictures," Stirling wrote of his colleague. "The bear was so well insulated it gave off no detectable heat at all. But there was a spot on the infrared photo, just ahead of the bear's head ... made by its breath!"

  So effective, in fact, is a polar bear at thermoregulation that even in temperatures that would threaten hypothermia in humans, its bigger concern is staying cool. This is the primary reason why its pace seems so unhurried: at temperatures between—4°F and—12°F, a bear's body temperature remains fairly constant when walking at about two and a half miles per hour; by the time it is moving at a mere four miles per hour, its body temperature may soar to 100°F. No wonder, then, that although adult bears are capable of bursts of high speed when launching surprise attacks on basking seals, those bursts are brief and, particularly if the seal escapes, followed by exhausted recuperation.

  When the ambient temperature is too high for comfort, polar bears respond by doing as little as possible, seeking out shade or shelter and lying still, expending no unnecessary energy and waiting for conditions to cool. Even the arrival of lower temperatures and the season's first ice and snow may offer only marginal respite.

  "Typically what you'll see them do is spread themselves on the ice, so their groin area can cool off," says JoAnne Simerson. "What I've seen them do, before there's snow and ice but the ponds are beginning to freeze, is actually punch through the thin layer of ice on the ponds and lie down and sit in the water."

  And, when sitting in water doesn't help, they can immerse themselves in it.

  Polar bears are excellent swimmers. They can—and frequently do—swim for hours at a time, although too prolonged an exertion can result in severe exhaustion and the need to recuperate for lengthy periods, and may be particularly dangerous for young cubs. The same long neck that enables a polar bear to plunge its head through ice holes and under water when hunting also allows it to keep its head above water for long stretches when swimming; and the fact that it is able to swim for long stretches owes a great deal to what are by far the largest feet in the bear world.

  At up to twelve inches in diameter—almost twice as big as a brown bear's feet—a polar bear's front paws are striking in their immensity; in the photograph at which I am currently looking, which I took on the shores of Hudson Bay a few weeks before writing these words, a resting bear is looking at the camera and at me, its muzzle lying on a paw that seems almost as large as its head.

  "They're like snowshoes," says Simerson; "it's all about weight distribution," a means of spreading the impact of a bear's bulk to make it easier for it to walk over ice. Indeed, when a bear is setting out uncertainly over ice that is particularly thin, it will often all but spread-eagle itself to distribute its weight as evenly as possible. But such large paws are also valuable for fatally swatting seals. And they make magnificent oars with which a bear can doggy-paddle through the water, while its rear legs curl up underneath its body and act like rudders.

  A polar bear's buoyancy is considerably aided by a thick layer of blubber, which not only helps keep a bear warm, but also enables it to store huge reserves of fat for lean periods and metabolize them when needed, a response to an environment of uncertain and uneven productivity. Polar bears frequently eat seemingly to excess when food is available and then slow down their metabolism substantially while drawing on fat reserves, a state known as "walking hibernation," when pickings are thin and food is hard to find.

  That layer of blubber can be as much as four and a half inches thick and is topped by skin that is, perhaps surprisingly, black. Equally surprisingly, a polar bear's fur is not actually white.

  It is in fact unpigmented, but because it reflects visible light it appears white to t
he human eye when it is clean and in sunlight. During sunrise or sunset, the fur may actually appear to take on the orange-yellow hues of the rising or setting sun; later in the season, in spring or late winter, before the annual molt that begins in April or May, bears may appear to be "off-white" or even yellowish.

  While sunlight is reflected off the pelt (contributing to its white appearance), the late Norwegian scientist Nils Øritsland found that some of it passes through and reaches the black skin, which naturally enough warms up.

  "Warm surfaces, of course, emit long-wave infrared radiation, or heat," notes Øritsland's colleague David Lavigne. (This is the principle behind night-vision optics.) "So the skin emits long-wave infrared and it turns out that, when it hits the hairs on the way out, they trap the heat inside the pelt."

  In other words, polar bear hairs let some of the sun's warming rays pass through, but they don't let the heat radiate back out. Not only that, but because the hairs are hollow, they contain air that is warmed by the heat trapped within the pelt, causing further warming.

  It is the final line of defense against the polar bear's most constant and potentially dangerous enemy, the bitter chill of its Arctic domain, and perhaps the most effective. (Although not, of course, in the very dead of winter, when there is no daylight at all. For the mechanism to work, it needs sunlight.) It is also a line of defense that has been frequently misreported and misunderstood.

  A polar bear hair does not, as Richard C. Davids writes, act as "a miniature light pipe that funnels only ultraviolet light down through its core to be absorbed by the black skin." That idea—that polar bear hairs not only trap heat from sunlight but actively channel the ultraviolet directly to the skin—is a myth, but a persistent one. Its origins lie in a misreading of both Øritsland's research on polar bear fur and another study he conducted with Lavigne.

  In 1974, the two men were attempting to determine a means of counting seal pups from the air that was more effective than searching for white seals on white ice.

  "We discovered that ultraviolet photography turns white seals black, and in the course of doing so, we discovered that ultraviolet photography turns most white animals black," Lavigne recalls. "We were in a hurry and wanted to photograph a white animal from the air, so we went to Churchill, Manitoba, and photographed a polar bear with three cubs, and they all showed up black. That led to a cover story in Nature called 'Black Polar Bears.'"

  The reason seal pups and polar bears look black when photographed in ultraviolet is that their fur absorbs UV radiation; conversely, they appear white to us in normal conditions because the fur reflects visible light. There is no obvious benefit to the bears—or the seals—from absorbing UV radiation in this way; as Lavigne noted, it turns out that most white animals do so, and later he discovered that the Canadian military's equipment, painted white to provide camouflage in snowy Arctic environments, did as well. *

  But subsequently, some American military researchers who had not been involved in either study conflated the two findings and, speaking to a reporter for Time magazine, described the process differently.

  "Now the ultraviolet hits the polar bear, gets to the hollow pipe which acts as a fiber optic, transmits this high-energy ultraviolet radiation into the skin, and then heats up the bear," says Lavigne, describing the distorted version. "But the problem is that the ultraviolet never gets to travel down the hair because the whole point of what Nils and I described is that it is immediately absorbed by the hair."

  Even so, what Lavigne describes as "the myth of the solar polar bear" endures. "Solar energy? Do polar bears hold the secret?" asked the Washington Post rhetorically in 1987. "Polar bears' fur holds clue to better lasers," insisted the London Sunday Times in 1995. Even the august Scientific American got in on the act, headlining a 1988 article simply and succinctly, "Solar Polar Bears."

  It endures partly because distinctions among visible spectrum light, infrared, and ultraviolet, among absorption and reflection and transmission, can be subtle and confusing. It endures because it is hard to fact-check when so many sources have repeated the story as gospel. But it endures also because it seems like something that should be true, that a magnificent animal in an almost impossibly hostile environment should have developed an almost fantastic mechanism for keeping warm.

  The pity of it is that the truth needs no elaboration. Every polar bear is so well insulated that not only does it boast a thick layer of blubber and a warm pelt, but that pelt warms the cold air that reaches its skin and traps it against its body, enveloping the bear in a thermal blanket. Polar bears, in effect, are mobile, furry greenhouses. That, by itself, is remarkable enough.

  As Robert Bieder has observed, the polar bear is a creature of paradox. It is a white bear with translucent hair and black skin. It is an enormous predator that walks softly and almost silently across the ice. It is an Arctic resident whose major problem is not staying warm but keeping cool. And the winter, when other bears are generally hibernating, is for the polar bear among the most active times of the year, as it stalks the ice in search of seals.

  To the members of a sixteenth-century voyage of exploration, it was a white bear "of a monstrous bigness." Eighteenth-century whalers dubbed it the "farmer," tending the ice fields across which it wandered. Scientists call it Ursus maritimus, the sea bear. But it is in Norwegian or German—where it is known as, respectively, ijsbjorn and eisbär —that the nomenclature most accurately describes the species.

  For these land carnivores that are officially classified as marine mammals are, above all else, creatures of the ice.

  Ice

  We were moving.

  It was morning, I was in my bunk, I had been asleep, and when I woke up I could feel the movement of the ship. I lay there, blinked a few times, rubbed my eyes, stretched, gathered my thoughts.

  We weren't supposed to be going anywhere. The previous day we had arrived off Barrow, the northernmost town in the United States, on the Beaufort Sea coast of Alaska. We had dropped anchor that afternoon; we were not scheduled to weigh it for several days, time for new crew to arrive and existing crew to leave, and to change the on-board complement of scientists and journalists.

  But we were unmistakably on the move. And yet, something about our motion didn't feel right. It was almost as if we were moving ... backward.

  Frank Kamp, the chief mate, had been the first to spot the impending collision. He had been on anchor watch, alone in the wheelhouse early in the morning, plotting our upcoming course on the chart, keeping the bridge tidy, casting an occasional eye out the window.

  The watch had been uneventful, as anchor watches often are. The Beaufort Sea current was strong, driving at several knots along the Alaska coast; but although there was some ice, it was not especially plentiful. Floes appeared sporadically, mostly passing harmlessly by; those that appeared to be on a collision course looked to be of little consequence, but even so, when necessary, Frank nudged the rudder just enough to lessen or avoid the blow. Not that the strengthened hull could not withstand the impact, but there was no point subjecting it to any more encounters with ice than absolutely necessary. Besides, a series of jarring, thumping impacts throughout the night and early morning would have done little to endear the first mate to his fellow mariners.

  As early morning dawned—the transition from night to day barely perceptible at this latitude in summer—the fog descended. Peering through the binoculars, Frank scanned what passed for a horizon, then paused. He lowered the binoculars, raised them again, wondering if his mind was playing tricks on him and finally realizing that he truly was seeing what he thought he was seeing. There was indeed an enormous ice floe headed for the ship, one that no amount of rudder turning could avoid. This one was going to hit, and when it did it was going to do more than briefly rouse a few people from their sleep.

  He rushed below to fetch the captain, but barely had the pair made it back to the wheelhouse than the floe struck. The force of a half-million tons, one billion pounds
of frozen water, drove into the Arctic Sunrise, and after token resistance the ship acquiesced to its demands. Now we too were headed along the coast at several knots, powerless to deny the urgings of the enormous piece of ice that had made us its plaything.

  The severity of the situation was not initially apparent to all on board. For many it was an opportunity to photograph sea ice up close, the dirty, gnarled mass stretching in every direction and providing grist for photographic mills. There was even the added bonus of a brief appearance of the anchor chain—which, as captain and mate deployed the ship's thrusters in a desperate battle to twist and turn the Sunrise free of its imprisonment, abruptly sped across the surface of the floe, anchor in tow, before disappearing anew beneath the surface. The cook, awakened by the brouhaha, stuck his head out of his cabin porthole, only to be rapidly reprimanded by those assembled on deck, fearful that the anchor and chain might make an unscheduled reappearance and ricochet into the unwary.

  But if not all those present immediately grasped the gravity of the predicament, Captain Arne Sorensen was all too aware of the dangers, not only because his years of sailing in polar seas had made him acutely familiar with the risks posed by marauding ice floes, but also because he had firsthand experience of their power to entrap the unsuspecting in their suffocating embrace.

  On October 27, 1985, Sorensen, then captain of the Australian research ship Nella Dan, was grinding northward through the sea ice surrounding Antarctica, threading his ship gently through a maze of open water that promised to provide safe passage to the relative sanctuary of the Southern Ocean. As he did so, an easterly wind arose as if from nowhere, pushing the floes into each other on all sides, compressing them around the hull and under the bow. Almost in a matter of moments, the ship lifted clear of the water and ground to a halt. Over the next few days, the broken ice froze into one enormous field, and the Nella Dan was completely beset. There it stayed, frozen in place, for seven weeks, until released on December 14 by the Japanese icebreaker Shirase. The severity of the Nella Dan's captivity was underlined by the fact that, having plowed without resistance through a seemingly endless landscape of ice on its way to perform the rescue, the Shirase was forced, upon arrival at the frozen Alcatraz that encased the hull of Sorensen's vessel, to back up and charge through ice that in one spot close to the Australian ship was measured at sixty feet thick.