Arctic Dreams, page 12
The wide walk of a fat bear in June, you would see, differs from the walk of a thin bear in October. Bear tracks would show a consistent avoidance of deep snow; in spring they would not cross melt pools, where needle ice can puncture a bear’s foot. On a sheet of sea ice so thin it would not support a human step, you would see traces where a bear had crossed with skating steps like a water strider, sprawled nearly on its chest.
These signs reveal that the polar bear lives in an olfactory and a visual landscape, and that it is attentive, especially in summer, to a thermal landscape. It looks for cool places.
From following hundreds of such tracks, polar bear biologists have developed certain impressions. Males keep largely to the coasts in summer, while females with cubs and subadults are more apt to travel overland from place to place. Bears make use of mountain passes, ravines, and other features of the land in such a way as to suggest that these are traditional routes across isthmuses as well as occasional one-time shortcuts around an area of bad ice or open water. (To take a shortcut, a creature must have a map in its head of where it is—memory is no help. How bears create and use such maps is one of the most intriguing of all the questions about them.)
Beyond using celestial clues and a knowledge of prevailing winds and currents, which reliably guide Eskimos across the angular topography of shifting sea ice, no one knows how bears find their way. But they consistently travel directly to aggregations of seals; they return to core denning and breeding areas every year; and they find their way unerringly to the coast from hundreds of miles offshore. This would be astonishing enough if they only did it on land, where there are perennial landmarks, but they also do it at sea, where a frozen landscape is created anew each year, where it can change from one day to the next with the sudden rise of a new pressure ridge or the opening of a lead, with a shift of pack ice in the currents. In some areas of stable ice, bears may travel for weeks without seeing a break in the continuity of the sharp blue line of the horizon, with only “the infinite expanse of the frozen plain, the infinite dome of the cold blue sky, and the cold, white sun” before them.
Gathering ground to themselves. Navigating. Wandering with purpose.
The large black nose pulls cool air continuously across the nasal membranes, straining it for scent. The female bear climbs on top of an old piece of multiyear ice and rises on her hind legs to scan the ice fields beyond. She shields her eyes against the brilliant March light with her paw. She goes on. Partway across a refrozen lead the bear pauses motionless, one paw off the ground. Her head tilts and the small ears pivot independently. She puts the paw down. She sniffs the air at several levels, then the head is still, the attention fixed. She has found netsik. And netsik, somewhere beneath the snow and ice of Viscount Melville Sound, knows, perhaps, that nanuq has come.
The relationship between the hunted animal and the hunter has only recently come to be studied with the same intensity that biologists have brought to the study of the isolated life histories of the individual species. A Canadian polar bear biologist, Ian Stirling, has added greatly to a Western understanding of the polar bear by combining his study of bears hunting seals with a study of ringed seals and ice dynamics. In the spring of 1974, Stirling, with the help of ringed-seal biologist Tom Smith, was able to explain a peculiar sudden decline of the polar bear population in Amundsen Gulf. In the winter of 1973–74, he said, little snow fell in the area—too little to permit seals to excavate their snow lairs on the ice except in a few isolated places. Also, the ice itself remained stable and unbroken in areas where there were usually leads in winter. Perhaps the solid ice also affected concentrations of the seals’ food. At any rate, a number of seals moved out (one of Smith’s tagged seals moved all the way to Cape Dezhnev, Siberia), very few seals made birth lairs, and many bears either starved or moved on. Because, in essence, it didn’t snow enough that year.
The ringed seal that the polar bear habitually hunts is a small marine mammal completely at home in the sea ice. Its short snout and large eyes suggest a cat’s face, though its sleek head is earless. Its short-necked, broad-shouldered, barrel-chested, tapered body is like that of its relatives, the harp, ribbon, and spotted seals. Like them, too, the ringed seal is awkward out of water because its hind flippers don’t pivot forward like a walrus’s or a sea lion’s to help it walk.
Ringed seals are the most abundant large mammal in the Arctic—the Russians estimate a minimal population of 2.5 million—but they are relatively unsocial, rarely gathering in dense numbers. The young are born in snow-covered lairs on top of the ice in’ early April. Eight to ten weeks later they are on their own. Adults breed in late April and early May, at about six years of age. They feed, interestingly, at two levels of arctic marine food chains, consuming both fish in the cod family and the zooplankton those fish feed on. Differences in age at weaning—if the ice breaks up early a pup is not nursed as long—partially account for the variety of size in ringed seals. An adult may range from 40 to 60 inches in length and weigh from 80 to 250 pounds. During breeding, nursing, and molting, ringed seals feed lightly and may lose as much as 30 percent of their body weight. They are also territorial at this time, sometimes so aggressively defensive around their breathing holes that young seals who have crawled out on the ice through the wrong hole are kept at bay by another seal in the water until they are frozen out.
Among many questions about the ringed seal are how it finds food beneath the ice in the darkness of winter and how it “remembers” the location of its breathing holes, particularly after a deep dive in ocean currents.
A ringed seal is most vulnerable to the polar bear when it surfaces to breathe. When it is hauled out on the ice it is unusually vigilant, looking up for six or eight seconds every twenty to thirty seconds, and napping so close to its breathing hole that it can usually escape. Seals in birth lairs and males and nonbreeding females in haul-out lairs under the snow present another set of circumstances, to be considered in a moment.8
From the polar bear’s perspective, the seal is a swift, alert animal that can be taken advantage of only at that moment of vulnerability—when it breaks the surface of the water to draw breath, or when it is hauled out. Bears stalk seals over the ice or approach by swimming quietly toward them. The patience and judgment evident in these stalks can rivet a human observer’s attention.
The bear we left hunting on Viscount Melville Sound had heard a seal surfacing in its snow cave, a muffled tinkle of water at its aglu as it pulled itself out. The bear’s footfalls are nearly soundless as it approaches—the hair between its footpads muffles the crunch and squeak of snow. The bear pinpoints in her mind the spot where the seal now rests. When she is 20 feet away—she pauses ten seconds at one step, fifteen seconds with another step, ears twitching to detect the seal’s movement—she lunges, comes slamming through the snow roof with all four feet centered precisely over the aglu. The seal is cut off, finished.
Sometimes all it takes to break in the roof of a seal’s lair is a single calculated blow of the 40-pound paw. But these are stout structures, and the bear may be forced to dig. Perhaps once in five times, overall, it is successful. It understands precisely, however, where in the chamber the aglu is, and its explosive entries into seal lairs of all kinds are almost invariably centered at that spot.
Probably no other predator employs as many hunting strategies with one animal as the polar bear does with the ringed seal. It may take a half hour to patiently approach a seal resting on the edge of an ice floe, surfacing quietly to reconnoiter, then submerging again. A bear may drift toward a seal like an innocuous piece of ice; when it reaches the floe edge it explodes from the water and smacks the seal dead all in one motion. When it stalks seals over the ice, it flattens itself on its forequarters and slides along slowly on chest and forelegs, taking advantage of every piece of cover. It will scrape away the sea ice at a breathing hole until there is just a thin layer left, and then cover the ice with its body to cut off sunlight, so it looks to the seal below as if the thick crust of ice and snow is still present. It will build a snow wall to hide behind while it waits at an aglu. And it will rise up suddenly in a resting seal’s own aglu.
Stirling, who has watched them hunting for more than 2000 hours in the field, emphasizes several points about bears. First, the bear is only occasionally successful. The overall hunting success in any particular situation, considering the variety of ice cover, the number of seals present, the time of year, the age and sex of the bear, and the age of the seal, might range from 2 to 25 percent. The highest rate of success for a technique that is persistently applied, in Stirling’s view, is the patient wait at an aglu for a seal to show up. (The bear can tell from small details of ice accumulation and sometimes by catching a whiff of seal odor whether the aglu has been used recently enough to make waiting worthwhile.)
Older bears, especially, have exceptional patience. They will wait for three or four hours at an aglu, lying downwind of the hole on their chests, out of the seal’s line of sight. To stretch its muscles a bear will sometimes rise to sit or stand up quietly, ready to drop again soundlessly if it hears a seal.
Just before it surfaces, the seal exhales, and the sight or sound of the bubbles alerts the bear. The seal rises headfirst up a cone-shaped tunnel to its breathing hole, which, on smooth ice, appears as a low mound. A small amount of water forced up ahead of the seal splashes out on the ice and freezes. (The seal keeps the tunnel open and the aglu from freezing over completely by scouring with its claws.) The bear must time its strike perfectly and move with exceptional speed. It usually strikes with one or both paws and follows so quickly with its snout that if the smashing blow of its paws doesn’t kill the seal, the impact of its snout will. “Everything cooperates,” writes Frans Van de Velde, “—paws, claws, snout, and teeth—to give a blow that is so rapid that the seal has hardly a chance of getting away.”
When it charges a basking seal, the bear does not seem so much to run as to pounce. Thor Larsen, a biologist who has observed polar bears in Svalbard for more than fifteen years, when I asked him about their hunting behavior, said, “Cats. They are like big cats.” Fast? “It is absolutely unbelievable how fast they are—oh, do they come fast.” Shrewd? “Yes. They are making judgments at every point about what to do. And they are patient.”
Larsen, Stirling, Dennis Andriashek, Schweinsburg, and other polar bear biologists with long field experience often comment on the bear’s seeming ability to analyze an unfamiliar situation and attempt a practical solution; on its ability to learn quickly when confronted with something new; and the novel approaches bears take to commonplace situations. “They are smart,” says Larsen, “and precisely because they are, they sustain all the legends about them doing these extraordinary things, like using tools and moving blinds along ahead of them.”
Bears prey on an impressive range of animals, each of which requires something different of the bear. They hunt spotted and ribbon seals in the western Arctic and harp seals in the eastern Arctic. The large bearded seal and hooded seals off the coast of Greenland are much stronger quarry. In leads and at savssats, bears prey on belukha and narwhals.9 Bears prey heavily on bearded seal pups and kill an occasional muskox, walrus, dozing hare, or goose caught flightless during its molt. They eat bird eggs, seaweed, varieties of tundra berries. And carrion. (A bear can live for months on a bowhead whale carcass or beach-cast walrus.) The bear also leaves carrion in its wake; and here lies an interesting aspect of its ecology. An adult bear in good health will usually eat only a ringed seal’s blubber, leaving the rest behind for a retinue that never seems far off—the arctic fox, glaucous and Thayer’s gulls, the shier ivory gull, and the ubiquitous raven. (In winter arctic foxes live far out on the sea ice, entirely dependent on scavenging polar bear kills for their survival.)
When a female with cubs makes a kill, on the other hand, the family normally consumes the whole seal carcass. But they also scavenge carcasses left behind by the adult males. While it is not clear how, it is evident that sharing these kills is critically important to a healthy polar bear population.
Polar bears are neither gregarious nor social, in the sense that, say, wolves or cheetahs are social. Their repertoire of body language and vocalizations seems limited, used largely to communicate a desire to avoid each other. When they are seen, they are usually seen alone—a single male or female, or a female with her cubs. They gather together in special circumstances, however, and some of these assemblies are memorable.
In 1874 two American observers saw between 250 and 300 polar bears together on Saint Matthew Island in Bering Sea, placidly “grazing and rooting about like hogs in a common.” (A ship’s captain who saw polar bears ranging together in a lush coastal valley in eastern Greenland likened them to sheep pastured in an English meadow.) At Cape Churchill, Manitoba, in September and October great numbers of bears are milling about waiting, like the Saint Matthew bears, for the formation of sea ice, so they can quit the coast and a life of sleeping and browsing in these summer retreats.
Food draws bears together in at least two ways. When a single bear finds a good seal-hunting ground, ten or fifteen other bears are likely to show up at the same place within half a day or so. Somehow they know. Savssats and beached carrion also draw bears. In 1980, scientists counted fifty-six of them at a bowhead whale carcass on the Svalbard coast. Larsen says scientists don’t have an explanation for how bears get wind of these things. Odor likely plays a role, but bears come in from all directions and some from very far away. “They just get to a place where something is happening,” says Larsen, “and they get there quickly.”
Bears seem to pay each other very little mind under these circumstances. They feed, interact very little with each other, and go on their way. It is a different situation entirely when a female with cubs encounters a lone male. She runs away immediately. Or when two males meet each other on the track of a female in estrus. The ensuing fights can be violent and protracted. (Fighting among males is so common that it is a rare male past the age of six that doesn’t carry facial scars from these encounters.) On the other hand, a little-understood pairing apparently occasionally occurs with young male bears who become hunting and traveling companions.
The enduring social unit is a female and her cubs. They are usually together for two years, during which time the female teaches the cubs to hunt. Their social interaction is constant and intense. Older bears infrequently make sounds—they hiss loudly, growl, and champ their teeth when they are irritated; and when they are very agitated they make a soft chuffing sound. Cubs, on the other hand, have an impressive vocal repertoire. When they are around human observers they hiss, squall, and whimper, make a wet, popping sound by smacking their lips, and emit throaty rumblings. Scientists guess that their mothers communicate with them vocally—perhaps using only a few simple sounds. One could be a version of the adult’s chuff, a quiet, repetitive call “easily located in space but not traveling far,” used to warn her cubs away from danger—an approaching male, rotten ice, a rabid fox.
Somehow the female must control her cubs until they can feed themselves, if for no other reason than that they can so easily disrupt her own hunting, on which they all depend. (One scientist suggested to me that females solve this problem by walking the cubs until they are so tired they curl up together to sleep. While they rest, she hunts.)
Young bears apparently understand the basic skills of stalking and still-hunting, but require practice. Perhaps their mothers also provide some instruction by creating opportunities for them; and perhaps they learn a good deal by watching and imitating. Their initial attempts to catch seals are frantic and impatient. A young bear may give up its watch at an aglu after only ten minutes. Or charge wildly across an ice floe and dive headfirst into a lead in pursuit of a seal. As with other predators, an acute sense of need plays a crucial role in the determination to succeed. For cubs-of-the-year (coys) and yearlings, mother will provide.
Polar bears have relatively few young, but they put a great deal of time and energy into raising and protecting them, which ensures that most of them will survive. When they are between twenty-four and twenty-eight months old, usually, the family breaks up and the cubs are on their own. The female often mates again. The cubs may stay together for a while, but then they, too, separate. At this point, the survival of Ursus maritimus hinges on learning to live alone. And among all age classes of bears, it is those in this transitional stage that suffer the greatest mortality.
Charles Jonkel, a biologist, summarizes the situation that faces a young bear in its first summer alone. First, it lacks experience, an indispensable attribute for a successful hunter. Second, it is somewhat limited in its ability to secure food because of its small size (a large bearded or hooded seal could get away); and it might not have strength enough to break through a seal lair before the seal escapes. Third, it has a pressing need for food, not only for its continued growth, but to build up a layer of blubber on which to draw during lean periods. Fourth, it has to learn to find its way, to comprehend and then remember the relationships between currents, prevailing winds, the position of certain land masses, the trend of coastlines. Last, it must face competition from and conflict with older bears, who may take its seals away.
A female’s unique competence lies in figuring out something new and difficult—den construction—in the middle of her life; and in teaching her cubs to survive. What makes the males impressive is their year-round success as hunters (for they are more often abroad in the winter than the female) and their assertive curiosity. Males investigate almost anything they spot on the sea ice. In evolutionary terms this might only be simple resourcefulness. Curious bears may in the end eat more often. The darker side of this is that, today, with the spread of oil camps and the abandonment of military installations, curious bears are sometimes killed by the things they test.
