The Great White Bear (5 page)

"Once she comes out of her den, she doesn't automatically leave right away," says Mike Spence. "The cubs need to become adapted to the environment. They've got a long journey ahead of them. It all depends on what condition the cubs are in. It depends on what condition she's in. They'll play, they'll get their muscles going, and then one day she'll decide it's time to go, and off she'll go."

Tom Smith has found that in Alaska, mothers and cubs tend to tarry at their dens on average two days before heading out for the sea ice, although some do so on the same day they emerge. During that time, if Smith and colleagues are able to watch the bears outside the den for one hour out of every twenty-four, they consider themselves fortunate. Often, he says, bears "will spend mere minutes per day outside the den. But then, why go outside? The environment is hostile and being outside also signals where the den is. They almost never nurse outside but again, why bother?"

Smith notes that staying at the den is both costly, in that it prevents the mother from hunting for food, and dangerous, as it advertises the den's location. At the same time, to leave too early, before the cubs are ready, would condemn them to certain death. "I'm convinced that the only reason mothers tarry at dens is to monitor cubs' growth and development," he says. "Once it meets some standard written in her genes, off they go."

The mother, desperately depleted after four months without food, nudges the young cubs onward, but for tiny legs that have hitherto been accustomed only to a small cave in the snow, it is a difficult journey. At times, particularly when danger may be near, the cubs clamber onto their mother's back. The travelers repeatedly stop and rest, the cubs nursing from their mother's milk and all three taking advantage of opportunities to nap and gather their strength. Eventually, they reach the shores of Hudson Bay, and the cubs gingerly follow their mother as she strides out, away from the beach and across the fractured and mangled ice, in search of seals to break her long fast.

Even as they reach the ice, danger abounds. Although the rate appears to vary by location, studies have shown that as few as 45 to 65 percent of polar bear cubs survive their first year. In Hudson Bay, where an abundant spring is followed by the completely barren months of late summer and early fall, the survival rate of cubs may be as much as 20 percent below that of cubs in the Beaufort Sea.

The first few days are especially dangerous. It is a jarring conversion from the quiet warmth of their den to the subzero temperatures of an Arctic spring. Sea ice terrain is uneven and treacherous. And along the coasts and on the ice, danger lurks.

Adult male polar bears have been known to kill and eat young cubs, although how often they do so is unknown, and why they would do so is unclear. It seems unlikely it would be a purely predatory action: a newly born cub would not provide much energy, skewing the risk/ reward ratio heavily toward the risk, particularly given the certainty of attack from an angry, protective mother. Perhaps, it has been speculated, there is a cold calculus involved: killing the cubs of another male decreases the competition and increases the survival chances of a male's own progeny. But that supposes that the male, having walked away from the female upon insemination, is able to distinguish between his cubs and those of others. Maybe, then, it is a means of improving his mating opportunities: as long as a female has dependent cubs, she does not enter estrus and become sexually available; without them, she is soon sexually receptive. But while such an explanation may make sense for brown or black bears, which have relatively small territories and could be expected to keep track of a female over the few days after she loses her cubs and before she enters estrus, it does not so readily for polar bears, whose ranges are considerably larger. Indeed, Steven Amstrup notes that on the two instances of infanticide he has observed in the Beaufort Sea region, male and female were already dozens of miles apart the following day and traveling in opposite directions.

Perhaps, speculates Amstrup, cannibalism of cubs doesn't actually serve any particular purpose at all. Perhaps it is a behavioral remnant from when polar bears were terrestrial, an atavistic anomaly that polar bears have not excised from their wiring. Ian Stirling, for one, thinks it happens only rarely and opportunistically. Yes, females do show a tendency to keep their cubs away from males, but they would be maternally remiss not to shelter them from hungry thousand-pound carnivores. And while it is not uncommon for males to move toward females with cubs, it is less common for them to be able to catch up to them, the cubs jostled along by their protective mother and all of them capable of maintaining a faster pace for longer than the heavyset males, which are large, well insulated, and quick to overheat when they run. When males do succeed in grabbing a cub, it is normally after surprising a family that is sleeping; if the mother is alert and able to respond, she will fight to protect them, even though the male is far larger. On occasion, it seems, she will do so even to the death: in two separate instances in 1984, researchers came across a male feasting on the carcass of a female, as her cubs cowered in the distance. In both cases, the scientists deduced that the male had killed the female; whether or not he went on to kill the cubs, they could not have survived for long.

Some cubs do not even make it as far as the sea ice, and ironically their mothers may be responsible for more instances of infanticide than any males. The physical strains on a pregnant female are immense, sometimes too immense. If, while preparing to make a den or even after settling into it, a female is not strong enough to see a pregnancy through to its conclusion, her body simply reabsorbs or aborts the fetuses, and she emerges from her den ready to resume sexual activity with the arrival of spring.

For some females, the physical limits are reached only when the cubs are born. By then it has been a long winter—for bears in Hudson Bay, eight months have already passed since their last meal—and the extra burden of rearing the newborns is a step too far. A 1985 paper in the journal
Arctic
cited seven reliably documented instances in which a mother was so malnourished that she killed and ate one or both of her cubs in order to survive. As Ian Stirling has written, "If there are seven documented instances of an event as difficult to observe as this, it may occur reasonably frequently."

The urge to survive, the overpowering drive to perpetuate her genes, that perhaps appears so cold when the polar bear mother devours her own young in order to increase her own chances of survival and thus of ultimately successful reproduction, seems to human eyes touching and warm when mother and cubs emerge from the den. She keeps them as close to her as she can: nudging them with her muzzle as they stand by her paws like uncertain children holding their mother's hands, or eager puppies keeping obediently to heel. It is a wonder that the mother does not trip over her offspring on a frequent basis, so tightly do they stick by her, winding around her paws, rubbing their heads against her legs. In time, they will grow up to be among the largest and most fearsome predators on Earth; now, they are vulnerable, largely defenseless, and insecure. Like any youngster taking its first steps in a frightening world, they want and need to stay close to their mother.

They will stick together, on average, for two years after emerging from the den, during which time their life will be, for all intents and purposes, a picture of familial bliss. The youngsters will tumble and play, staging mock battles, rolling over each other in the snow as their mother watches over them warily. They will curl up with her in pits in the snow, to sleep and suckle. And they will follow her closely, watching and tracking her every move, and for all that period of time, she will suckle them, even as she teaches them to hunt the seals that will constitute their diet for their entire adult lives.

During their first summer, the cubs will do almost no hunting of their own. They will, however, watch their mother closely and follow behind, sniffing where she sniffs, looking where she looks, lying down and waiting patiently when she begins to stalk or wait for prey. Occasionally, the waiting will prove too much, and the cubs, bored, will either pad up to their parent to see what is happening or will turn their attention to each other, biting, cuffing, rolling around, and running back and forth on the snow and ice—behaviors that sometimes earn a sharp rebuke from a mother anxious that her opportunity for a meal will be extinguished by such loud tomfoolery.

By the time the cubs are a year old, they have begun to hunt for themselves more often, but both the time spent doing so and the success rate of their efforts are substantially less than their mother's. With the passage of one more year, they have become significantly more adept: whereas yearlings and two-year-olds spend between 4 and 7 percent of their time hunting (as opposed to between 35 and 50 percent for their mothers), the former generally succeed in catching, on average, one seal every twenty-two days, while the latter have improved their success rate to one seal every five to six days.

Clearly, in that extra year the cubs have learned a great deal more from watching their mother, observations that have enabled them to become significantly more successful in their hunting. Their improvement is aided also by their growth, which gives them the extra strength needed to be able to kill and overpower a seal, and which is still fueled primarily by the nutrients from their mother's milk. That milk gives them strength, but its constant availability lessens the incentive for the cubs to refine their hunting skills with the rapidity that might be desired.

And so, once the cubs have reached roughly two and a half years old, once they have made it through their second winter in the open and grown big enough that they have enough fat reserves to survive the immediate future, they are forced to strike out by themselves.

Three years after she last mated, the cubs' mother is once more entering estrus. For the first time since conceiving, she is sexually receptive. The scent she exudes advertising her status attracts mature males from miles away, who now begin descending on the family's location. For the cubs it is a new and uncomfortable experience. For as long as they have been alive, their mother has protected them, kept them a safe distance from any inquisitive male. Now she welcomes her suitors' advances and rejects her cubs' attempts to seek sanctuary from their presence.

Scared, the cubs retreat from their mother and the approaching male. Confused, they look longingly after the retreating figure that has been the central focus of their entire lives. They start toward her, stop, look anxiously in the direction of the new arrival, and hesitatingly move away.

Finally, instinctively, they understand. They pace nervously back and forth, and they subconsciously move closer to each other as they moan uncertainly. The first phase of their lives, in which they relied almost entirely on their mother for nourishment and protection, is over. Now they must begin the second phase, the most dangerous few years of a polar bear's life. In the wind and snow, they huddle closer.

For the present, they have each other.

Otherwise, for the first time in their young lives, they are entirely alone.

The warming rays of
the sun have long since dipped beneath the horizon; the cold and the dark hold the Arctic in their thrall, and the sea has frozen into a largely solid mass.

Across the Northern Hemisphere, the sun's gradual withdrawal heralds a gathering calm, a comparative stillness as a season of plenty yields to one of paucity. Summer's kaleidoscope of colors and cacophony of bird song surrender to winter's monochrome quiet. Priority is placed on the conservation of energy, rather than its exuberant expression. Resources are at such a premium that many mammals choose to enter a form of stasis, a metabolic depression known as hibernation, in which the body temperature drops and breathing slows. It is commonly assumed that among those species that hibernate are North America's bears, but the assumption is inaccurate. Both grizzlies and black bears do submit to periods of prolonged sleep during which they can, if undisturbed, sleep without stirring for much of the winter. But their body temperature falls only a few degrees, and they can be easily roused. It is not true hibernation.

The winters from which brown and black bears shelter are mild compared to the one that two young polar bears are about to experience, but for them there is no hibernation. In fact, winter, while lacking the abundance of spring, is not for polar bears the harshest season; in contrast to the experiences of their relatives, that distinction falls to summer, when ice is at its minimum, water is at its maximum, and the seals on which they prey are hard to reach. For these two bears, the onset of winter is a good omen; as they huddle against each other for warmth, looking not as fat as perhaps polar bears should, they could, were they able to consider such things, comfort themselves with the knowledge that the worst was over. They had survived their first summer alone. Now they needed only to make it through the long polar night, and soon they would be witnessing the new dawn of spring.

As they bed down, one of them lifts his head into the air. He is sniffing, thinking that he has perhaps caught a tempting smell drifting on the wind. As he sniffs, he does not see, in the clear night sky, the stars twinkling far above, or that one star appears to stand almost overhead hour after hour, night after night, seemingly never moving even as the others circle perpetually around it.

In recognition thereof, it is dubbed Polaris, the pole star; and in the imaginative menagerie of celestial creatures compiled by ancient, wondering eyes, it is at the tail of a small bear, which we know by the Latin name of Ursa Minor. Nearby, another loose assemblage of stars that in reality are billions of miles apart have been stitched together to create Ursa Major, the Great Bear;
^*
and while the polar bears that stride across the ice below are the unquestioned rulers of the northern realm, it is Ursa Major after which their kingdom is named.