On the face of it, a ringed seal does not look very obviously more appealing to a polar bear than any other seal. At about five feet long and 150 or so pounds, an adult may be as little as 20 percent the weight of a bearded seal and be thus theoretically one-fifth as desirable. Pelage aside, it does not appear markedly dissimilar to most other seals, either. There is, however, one key difference.
At the end of its flippers, a ringed seal boasts five sharp, curved claws. These claws allowed the ringed seal to carve its own unique and lucrative niche in the Arctic marine ecosystem, for whereas other Arctic seals wishing to take a quick breath or a longer breather are obliged to make use of natural openings caused by the constant grinding, crashing, and splitting of ice floes, ringed seals can use their claws to create breathing holes of their very own.
"When the first molecule-thick layer of ice forms on the surface of the ocean, it's no big deal for a seal to push through that to breathe," says Kelly. "But when it gets many layers of molecules thick, when it gets inches thick, a bowhead whale or a walrus may be able to break through, but the small head of a ringed seal can't. So they reach up with these stout claws on their flippers, and they scratch a hole through the ice and poke their nose out to breathe."
As a ringed seal approaches a hole from beneath, it may pause, perhaps swim back and forth once or twice, and as it prepares to head upward and into the open air, it will blow a stream of bubbles ahead of it. The bubbles burst at the surface and in so doing, they clear away any detritus—bits of snow or ice—that may have accumulated. Ringed seals do this, Kelly suggests, not because such detritus blocks their passage but because it blocks their view, and a surfacing ringed seal is very keen indeed to try to ascertain whether anything is waiting for its emergence.
For, as much as the ability to create breathing holes has allowed ringed seals to flourish, it has also painted a target on their collective backs. A ringed seal will typically maintain no more than a half-dozen holes during the course of a season; in theory, all a bear need do is identify the location of a hole and be patient. And polar bears are nothing if not patient.
As fall progresses, snow accumulates on top of the holes, concealing them and insulating them. Ice continues to form, but with the snow's insulating warmth, it does so more slowly now than before. If the snow forms into a drift, a seal can, should it be so inclined, reach up into the snow and begin to carve out a snow cave. The cave functions as a place for the seal to haul out and rest on the ice, and while it may take advantage of the protective den for just a few minutes, it may also stay there for close to twenty-four hours.
Many of the caves, says Kelly, are quite beautiful inside.
"If you put your head in a snow cave and look up, there are these beautiful feathery crystals that hang down," he says. "It's frozen seal breath that's condensing on the ceiling and making these chandeliers, and the crystal light that's filtered through the snow is heavy in the blue spectrum, so the whole thing has a blue glow to it. It's just exquisitely gorgeous. I've looked at thousands of these things and every one of them is like a little chapel."
Some of them become not just chapels but maternity wards. In a fascinating echo of the polar bears' dens, it is in such caves, known as lairs—which, just like polar bear dens, may contain several chambers—that ringed seals give birth to and nurse their young.
Just like polar bears, ringed seal mothers must make their lairs in places where there is drifting snow. On the Arctic sea ice, that is almost invariably on the leeward side of pressure ridges formed by floes that have ground into each other, or where the pack has forced itself up against the fast ice and thrust small mountain ranges into the air.
But while polar bear mothers and cubs rest soundly in their dens, seemingly unconcerned by almost any disturbances that may pass by outside their cocoon, ringed seal mothers enjoy no such security. For patrolling the ice outside their snowdrifts, there is a very real threat.
The abundance of seal pups, and the inability of those pups to recognize or react to the danger posed by the prowling predators, makes springtime a time of plenty for polar bears, the time of year when food is both most plentiful and most vulnerable. (Their second most productive period, it seems, is early in the winter, when the rapidly freezing ice forces ringed seals to return to their breathing holes with great frequency to keep them open.)
The surface of the sea ice becomes a study in bear bacchanalia, polar bears feasting almost at will as they sniff out and crash through the lairs that have been painstakingly carved into drifts. It is a testament to the evolutionary and ecological success of ringed seals that, despite the massacre that is visited upon their young every spring, they continue to thrive.
The feeding frenzy is necessary; by the time the gorging is over, spring is well advanced and summer is fast approaching. The sea ice splinters, breaks apart, and melts; the watery leads become chasms in which seals can surface without fear of assault.
The bears are forced to retreat to ice that is thick or sheltered enough to persist during the warmer months, or even onto land, to await the time when temperatures drop once more, when the surface of the water freezes anew, and when they can once more wander, for mile upon uninterrupted mile, across the sea ice that is their unchallenged domain.
Life
Alone except for each other, the young polar bears face the most difficult period of their lives. If they survive to full adulthood, the age of five or six when they become sexually mature, their chances of surviving deep into old age are high; Ian Stirling has written that natural mortality in adult polar bears is so low that they are "virtually immortal." But the two and a half years until that time, after their mother has left them and before they have grown into full-size adults, are fraught with risk and challenge.
For two years they watched their mother, learned from her, and copied her every move—sometimes playfully, sometimes with more serious intent. But even as they began to hunt and kill seals, they did so with less frequency than she did and continued to rely on her milk for sustenance and certain survival. Now that option is no longer available to them.
They at least have the advantage of abundance, for the time of year in which they were left to fend for themselves was the same as when they first emerged from the den, when a profuse supply of young seals is theirs for the taking. But they must continue to refine their skills, and rapidly, in order to capitalize on this bounty; they must build up their fat reserves as extensively as they can in order to prepare themselves for the lean times that lie just a matter of weeks ahead. They must display the patience they lacked as occasionally dilettante hunters in their mother's company, expend far more time waiting for seals to emerge from their breathing holes, and not waste the opportunities that present themselves when seals do poke their heads out of the safety of the frigid water below. In the harsh Arctic environment, there is no margin for error.
If dogs dream of chasing slow-moving rabbits through grassy fields on a sunny day, then for a wishful, dozing polar bear, paradise is surely a place in which sea ice cover is plentiful and solid, but patterned with cracks large enough for a lazy seal to poke its head through and linger invitingly.
When it rouses from its reverie, the dozing bear shakes off the snow that has settled gently on it during its slumber and rises slowly to its feet. It sniffs the air, blinks softly, and then, after a final shake of its head, it walks.
The Inuit of northwest Greenland call the polar bear pisugtooq, "the wanderer," for that is what it does. When it is not sleeping—and polar bears, like humans, sleep for approximately eight hours out of every twenty-four—it is walking. Its stride is languid, apparently without aim or intent; but it is alert at all times, and the moment it sees or smells a seal on the ice—often from a distance of several hundred yards—its demeanor changes in an instant.
It immediately stops, stands perfectly still, and waits, staring at the seal, sometimes for several minutes, as if sizing up the distance to the prey. Then, slowly but surely,
it begins its stealthy march. As it moves forward, the bear lowers its head; once it draws within striking range, it sinks to a semi-crouch.
That polar bears are found throughout the Arctic but nowhere in the Antarctic is evident in the behavior of seals at both ends of the Earth. In the Antarctic, seals that have hauled out onto the ice observe approaching explorers or researchers, whether on foot or ship-bound, with mild curiosity but little if any alarm. Save for the restrictions imposed on such behavior by Antarctic Treaty regulations, it would be quite possible to walk up to a basking seal and not elicit much or even any alarm until close enough to reach out and touch it—and often, not even then. For there are no land predators in Antarctica, and a pinniped on the ice is in danger only if it has chosen to repose on a floe that might be tipped over by an observant killer whale. In contrast, ringed seals in the Arctic are bundles of restless energy, napping for perhaps a minute and then lifting their heads to scan their surroundings for several seconds, their large eyes on the alert for any movement, their sharp hearing tuned to detect anything untoward. As soon as a seal tenses in response to the sight or sound of movement, or merely raises itself onto its front flippers for a precautionary inspection of its immediate environment, the bear freezes in its tracks, able to hold its position without a wobble or a twitch, until the object of its attention, apparently unable to pick out the whitish mass of the approaching menace from the background or detect the gentle padding of its paws on the ice, lays down its head once more.
Slowly, surely, the bear closes in on its target. Then, suddenly, it charges.
Polar bears are not built for sustained speed; their heft and insulation work against them and they soon begin to overheat. But over distances of forty or fifty feet, they are capable of shockingly explosive bursts, and the moment they close to within that distance of their target, they take off, pounding forward with no further pretense of subtlety or subterfuge. One can only imagine the overwhelming shock and panic that must crash like a tsunami over the seal as this monstrous beast appears as if from nowhere, casting aside its cloak of invisibility and roaring toward it with frightening resolve and force.
Desperately, the seal flops toward the nearby breathing hole through which it emerged onto the ice, and its frantic bid to seek the sanctuary of the water that must suddenly seem so far away is an illustration of why ringed seals predominantly haul out of the ice by themselves and not in groups of several: a mass of blubbery bodies flopping pell-mell for safety would obstruct one another's passage so that each and every one of them would be at the bear's mercy.
(Indeed, notes University of Alaska ringed seal expert Brendan Kelly, those occasions when numerous seals do haul out by one hole frequently have entirely predictable outcomes. "When such groups are alarmed, they all try to escape down the hole at once," he says. "Most often that results in two or three seals with their heads submerged but their bodies unable to squeeze in at the same time. It is almost comical to see their hind flippers flapping madly in the air.")
As it is, by the time the seal reacts to the thundering onslaught, it is too late. The bear's jaws clamp shut around its head, then again, then again, before the predator hauls the carcass away.
A stalking polar bear does not always approach across the surface of a floe. On occasion, after staring at the intended victim as if to memorize the route, a bear will quietly slip into the water and swim through breaks in the ice, surfacing to breathe so stealthily, writes Ian Stirling, "that only the tip of the nose breaks the water between dives as the bear moves closer to the seal." Finally, Stirling continues, "it gets to the last available breathing hole before reaching the seal and slips out of sight again. After an eternity of suspense-filled seconds, the water in front of the seal explodes as the bear suddenly claws its way onto the ice after its prey."
While that may be the most spectacular mode of attack, it is not necessarily the most effective. More often than not, Stirling notes, the seal manages to evade the bear's claws and slip into the water, sometimes just inches ahead of the pursuing predator. More successful is a variation on the theme, in which bears approach their prey by means of the water-filled channels that form on top of melting sea ice in the summer, slithering along almost completely out of sight until close enough to strike.
One bear that used that particular technique showed such intelligence and awareness that even Stirling, who has studied polar bears in the wild for more than thirty years, was taken aback. After spotting a seal lying on the ice, he records, the bear stopped in its tracks and stared intently, without moving, for several minutes at a series of channels in the ice that led toward its potential prey. Then it quietly slipped into one of them and paddled gently ahead. So far, so unexceptional; what stunned Stirling was what happened when the bear came to a fork in the channel. Initially, the bear turned right at the fork; but after proceeding "about a body length," it stopped and, without lifting its head, backed up and then took the left channel, which was the one that led to the seal.
"I was amazed," Stirling wrote. "I have seen several bears lift their heads slightly to check their bearings but I have never seen such a demonstration of conscious memory."
Polar bears are more likely to use stalking as their means of predation in summer, when the ice is melting and narrow leads have widened to gaping channels, when the seals that haul out to rest do so in the open air. In fall and winter, those same seals take advantage of the breathing holes that they maintain in the ice, which are nominally hidden and protected by the seemingly anonymous snowdrifts that form over them. But a ringed seal's sanctuary is one that a polar bear's powerful sense of smell can pinpoint literally from miles away.
A polar bear zeroes in on a seal sheltering within its lair in the same way it does on one that is basking in plain view: its apparently aimless wandering comes to an abrupt halt, its nose sniffs the air. The bear may clamber onto a pressure ridge to gain a better sweep of the area, may move its head from side to side as if triangulating the scent and confirming the direction. Then it sets off toward the hidden bounty until, as it closes in on the lair in question, it suddenly speeds up and then, at the last moment, rears up on its hind legs and drives its forepaws down with a crash through the roof.
"A lair might be a meter, could be five meters long, and might have multiple chambers, but somehow, from that point on a pressure ridge, a bear is able to figure out not only which snowdrift to go for but also at which point in a snowdrift to make a hit," marvels Brendan Kelly.
If the bear is lucky, its attack crashes the roof onto the breathing hole itself, blocking the exit and trapping any seal that had been lying in the snow cave. Sometimes, however, the seal slides through the hole and into the water in advance of the bear's final lunge, or had already recently vacated its rest area.
When that happens, the bear will wait.
At times a bear must wait very patiently indeed, for perhaps an hour or even more. Most of the time, it will lie quietly on its stomach and chest, its chin close to the breathing hole or ice edge. It must remain not only still but completely silent: even the slightest movement on the ice is magnified as it reverberates into the water below. Such is the patience that some of the first explorers and naturalists to observe the behavior assumed that the bears were sleeping on the ice.
Bears do not, contrary to popular myth, cover their black noses with their paws to make themselves completely white. An extension of that story posits that it is always the right paw that covers the nose, and that all bears are left-handed—a wrinkle that also, from hours of observation of bears swiping seals with either forelimb, appears to be inaccurate.
Another tale, yet to be disproved, is that bears will, at least on occasion, be inventive: that they will, for example, build walls of snow behind which to hide as they wait at a breathing hole, or even that they will push blocks of ice ahead of them as they creep forward during a stalk. Although both prompt the raising of an eyebrow, the latter seems especially improbable; seals are as attuned to
the aural as to the visual, and the sound of ice scraping against ice would be far more likely to carry into the water and the ears of an attentive seal than the gentle padding of a predator's paws. (It is more likely that bears may push snow ahead of them with their noses as they crawl; polar explorer Eric Larsen recalls that a bear that apparently was stalking him on the ice of the Arctic Ocean in 2005 was doing just that.)
There is, however, some circumstantial evidence for another claim, that bears will sometimes use tools—specifically rocks or blocks of ice—to break through the most resistant of snow caves. Bears in captivity have certainly been observed to throw pieces of ice, and Erik W. Born relates this tale from Inuit hunter Kristian Eipe, who encountered the body of a recently killed walrus: "Before the bear had sat down to wait for a walrus to come up for air, it had fetched a lump of sea ice from the tidal zone," Eipe asserted. "It had prepared the lump of ice so that it was completely smooth, thereby making a tool which it could use to smash the walrus on the head ... The bear's claws had made deep marks in the fresh ice. It had attacked and hit the walrus on the head with its weapon ... The bear had crushed its skull from the muzzle to the back of the head, the skin there was torn to pieces, such was the force of the blow." In 1972, H. P. L. Kiliaan of the Canadian Wildlife Service was sledding across Sverdrup Inlet on Devon Island with two Inuit when one remarked he had seen a place where a bear had used a block of ice to smash a ringed seal lair. The three went to investigate and, reported Kiliaan, found a lair that had been broken open, the tracks of a female bear and two cubs, and, next to the breathing hole, a chunk of freshwater ice he estimated to weigh about forty-five pounds. By following the tracks, Kiliaan deduced that the bears had broken the ice from a much larger piece and then rolled it toward the breathing hole. He wrote: What happened next is not certain, but we may consider the following possibilities:
The Great White Bear Page 9