Polar bears (Ursus maritimus)
The polar bear is one of the few animals that occupy a realm that is largely without human population, and so some of the principal conservation issues that relate to it are unique. Whereas habitat loss is probably the most significant reason for decline in bear populations in other parts of the world, it is a less important factor with regard to polar bears. There are cases where human settlement and activity impact polar bears and their habitat, but in general we do not vie with polar bears for their territory, and their range is not in decline. Similarly, conflict with human beings, perhaps the other most significant factor in the decline of bear populations, is less of an issue with regard to polar bears, because interactions with people are so limited that the number of conflicts is very low. Conflict with polar bears has the potential to be very serious, but most problems that have occurred have been confined to specific areas that make up a tiny portion of the overall range of the polar bear.
Perhaps it is partly because of its obscurity that even in its reality the polar bear is partly mythical to us. Many people believe that the great white bear is the ultimate predator, and that it kills relentlessly and without motive. One of the main reasons for such beliefs may be that the polar bear has some uniquely adapted hunting skills, and, if anything, that we observe something of our own calculating and stealth in its behaviour and hunting methods. In general, we are attracted to the biggest and most powerful in any sphere, so that it is the grizzly bear and not the black bear that we hope to see the most when we visit the mountains, the lion and not the leopard when we are on safari. Seldom, when we see such animals do we report on our interaction in a calm and objective way, but, rather, we exaggerate for our own sake, perhaps to try and profit by association. This is the way we make legends, and the polar bear is the subject of many legends. So the polar bear has found its way into our desire and imagination, because it is so powerful, and because it is so much the undisputed king of its realm.
The reality of the polar bear could perhaps disappoint some people, in that many of its behaviours and traits are similar to those of black and grizzly bears. The polar bear adapted from grizzly (brown) bears that moved north, and it is believed that the two species 'separated' about 200,000 years ago. Polar bears and brown bears are so closely linked, in fact, that if they were to interbreed they could produce fertile offspring. The southernmost polar bears in the world live in the James Bay and Hudson Bay areas of Quebec, Nunavut and the Northwest Territories. The continental climatic influence on these inland seas resulting in their being frozen for six months of the year, providing a southern peninsula of habitat that would not otherwise exist. At the southernmost extent of their range, polar bears live at the same latitude as London, England, though in a far harsher climate. At the extreme north west of the range of the brown bear, there is some intersection with the range of the polar bear, so, while the possibility of interbreeding is remote, if it were to happen, that is where it would be most likely. Polar bears are a true global species, existing in North America, Europe and Asia, and, in the far north, they have been documented moving round the world on the ice.
There is very little difference in the size and weight of mature adult male polar bears and Kodiaks. In each case, mature males may weigh up to as much as 2000lbs, though more commonly they will average between 800-1200lbs. Sexual dimorphism in polar bears is very marked, with males often weighing twice as much as females, a factor which may partly be explained by males having significantly longer feeding periods than breeding females. In the Hudson Bay and James Bay areas, polar bears look very much like white grizzly bears, having short necks and broader heads with 'dished' or slightly convex faces. Further north, the bears have a more aquiline appearance, with longer necks and smaller, narrower heads. It is possible that this is an adaptation to more time spent in water, a kind of streamlining. Despite these differences, polar bears were never divided into distinct sub-species as brown bears were until recently.
Polar bears have black skin, which helps to absorb heat. This is only evident if one looks closely at a bear's face, or if the animal has a scar. Their hair is hollow, containing a thin column of air, which gives it exceptional insulation qualities. The feet of the polar bear have a thick covering of hair between the pads, and recent research has shown that the pads themselves actually give out enough heat to very slightly 'melt' the surface of the ice underfoot, enhancing grip. In combination with hooked claws, like that of a black bear, the polar bear is very well equipped to travel on ice.
Polar bears are almost completely carnivorous, being largely reliant on ringed seals (Phoca hispida) for food. Like most bears they are opportunists, and they will feed on other animals or carrion, but they are most adapted to ranging over the ice looking for seals' breathing-holes, and trying to catch them when they come up for air. As this suggests, polar bears are reliant on ice for their hunting. In the Hudson and James Bay areas, the bears only feed when the bays are frozen, which means they do not hibernate, as winter is by far their most active time. In the summer, the bears go through a period that is termed 'walking hibernation', where they are awake but conserving as much energy as possible. At this time, the bears rest and try to stay cool, as they are uncomfortable in temperatures above freezing. In some cases, they will excavate shallow dens, exposing the permafrost, and they will then lie on these ice-benches to keep cool. Apparently, during this ice-free period, polar bears spend up to 87% of their time resting.
During the brief summer months, the bears feed very little, relying instead on the fat stored by the previous winter's hunting. They become more opportunistic during this time, and will feed on stranded mammals and fish, small land mammals and even reindeer. They will also catch sea birds as they sit on the water, and they may eat berries if they come across them. Scat found during this ice-free period may contain some seaweed, and it is thought that the bears eat this in small quantities as a mineral supplement, much the same way ungulates will lick at mineral deposits where they come to the surface or are exposed. Feeding during this period is supplemental compared to feeding during the winter, which permits significant fat deposition.
For male bears and non-breeding females, this fasting period is generally from June or July to November, when the bays are ice-free, but for pregnant females who den from October or November until February, it is twice as long. When the female bears emerge with their cubs, having emaciated to about a quarter of the weight they carried on entering their dens, they have as long as the ice remains to regain their fat and feed their cubs adequately to allow them to survive to the next winter. As if this daunting task were not enough, the female polar bear must also defend her cubs from potential attack by males, who, like other bears, may try to kill cubs, particularly male cubs, if they have the chance. Climate change in recent years has meant that the ice in these southern areas of the polar bear's range is forming up to two weeks later than it did in the past. Similarly, in the spring, the ice is melting that much sooner, so the net result is that the feeding period for female polar bears with cubs has shortened by about 25%. If this proves to be a long term trend, or if this reduction increases, it is likely to make these southern polar bear populations non-viable, causing them, inevitably, to shift north.
Further north, where the ice is permanent, the bears do not have a fasting period, though food is less abundant, and climate and activity mean that a constant supply of food is necessary. The abundance and more moderate climate of the southern part of the range is what makes the bears' survival through the ice-free period possible.
Mating occurs on the ice, between March and June, and pregnant females den in the fall. Dens are usually located within 8km of the coast, though in the southern Hudson Bay region, they are concentrated in a 'traditional' denning area that is 30-60km inland. The protection of this denning area is one of the main reasons for the designation of Wapusk National Park. Because implantation of the egg is delayed, gestation lasts from 195-265 days, and cubs are born between November and January. At birth, cubs weigh about 1 *lbs, and they remain in the den until March or April, by which time they weigh 20-40lbs. Generally, polar bears will have twins, though singles and triplets are quite common. As with grizzly bears, quadruplets are rare. In cases of triplets or quadruplets, it is common that one or two cubs will not survive to maturity. It is quite common to observe polar bears with single cubs, which, because twins are more common than singles, suggests that many sows lose at least one cub. After spending a week to 10 days close to the den, for the cubs to get used to being outside, and using their limbs, the sow will then begin heading towards the ice to begin feeding. This is a vulnerable time, as the sow will not have fed for approximately 8 months, and the cubs are completely dependent on her.
Normally the cubs will stay with their mother for two years, unless she does not become pregnant again in the fall of their second year. Initially, after separating from their mother, siblings may remain together for some time. It is quite common to see three and four year-old bears playing and sparring together, and in many cases the bears in these situations are siblings. Play is an important part of the early years of a polar bear's life, and through it they learn about social interaction and, in the case of males, it prepares them for a time during future mating seasons, when their sparring will be more serious. Sexual maturity is reached between 5-6 years, on average, being earlier in females, and adult weight is reached at about 5 years by females and 10-11 years by males.
Polar bears, like black and brown bears, can live to between 25 and 30 years, and in some ways, are more likely to reach their potential longevity than any other species of bear. This is largely because there is little overlap between polar bear habitat and that of human beings, and, unlike the brown bear, there is little difference between their historic and present ranges. Particularly in the high Arctic, polar bears inevitably succumb to the elements of their harsh environment, old age making them less successful at hunting, leading to gradual starvation which, in turn, makes them still less able to find adequate food. Eventually, starvation and, ironically, the cold, combine to kill them. Older bears are also sometimes killed by younger, stronger bears in fighting over females during the mating period; these things are all reflective of the harshness of the life cycle and the environment of the polar bear.
The polar bear is a formidable hunter, and that, combined with its size and the fact that so few people know very much about it, has resulted in it becoming more the subject of legend than almost any other animal. Among the many indigenous peoples who live within the range of the polar bear, the bears are often powerful symbols and spirits, playing important roles in both history and modern culture. In many other societies, the polar bear has gained a reputation for being the most dangerous animal in the world, and for attacking and killing people and other animals for no reason. While people should have a healthy 'fear' and respect of the polar bear, as it is unrivaled in power and speed and adaptation to its environment, the way it is regarded is generally unfounded and based in ignorance, which is the case with many animals that acquire legendary status.
In reality, the behaviours of the polar bear are quite similar to those of other bears. Polar bears are very specialised hunters, but rather than being cold-blooded, they simply hunt in ways that permit them to sneak up on their prey without cover. There are three main hunting methodologies, the first being the scenting of seals in their den; having approached the den, the bears use their front paws like rams to smash in its roof, giving access to the seals inside. Dens make a significant contribution to the diet of the polar bear, as seal pups are very rich in fat. The second main hunting method involves lying in wait by a seal's breathing-hole, for the seal to surface for air. As proof of how potent a predator the polar bear is, there is an account of a bear waiting by a hole in the ice through which a beluga whale surfaced for air. While the 3-ton whale still had upward momentum, the bear seized it with its claws, and dragged it out of the water onto the ice! The other main hunting methodology is 'aquatic stalking', in which the bears use rivulets on the surface of the ice to approach resting seals while largely submerged.
What these methods have in common is that they are all very highly adapted, requiring calculation and intelligence more than just stealth. It is partly because of this capacity that the polar bear has gained such a notorious reputation amongst human beings; unfortunately, we often learn better from unfounded fear than we do from objective lessons. In his book "Arctic Dreams", Barry Lopez describes polar bears hunting seals on the open ice, crouched and moving directly towards them so that they are camouflaged other than for their black nose. Lopez claims that in such a situation, the bears seem to understand that their nose stands out and may give their presence away, and that they may cover them with their paws as they approach they seal! He also theorises that the bears may understand that if they approach the seal directly, it may not recognise what the nose is nor how far away it is, effectively becoming mesmerised by it, and so sometimes the bears will leave their nose uncovered as they approach. By the time they do realise what the nose is, the bear is generally so close that the seal cannot get away. If these things are true, they are very good illustrations of the great intelligence and adaptability of the polar bear.
For human beings in the arctic, polar bears are a very significant consideration, but their behaviour can, in general, be compared to that of the brown bear. They are similarly predictable, and they are no more given to tendencies that do not profit them or ensure their safety or the safety of their young. Given due warning of human presence, polar bears will avoid us, and they have far too pressing a task to gain and maintain fat to be distracted by some whim to kill for pleasure. That said, polar bears are almost completely carnivorous, and their environment is relentlessly unforgiving in demanding that they be equipped to survive in it. Because of this, there is certainly the potential that an unprepared or ill-equipped human could fall victim to a polar bear, although we are not a prey species to them. Theoretically, bears in the areas of Canada's Hudson or James bays, who do not feed during the summer could be more dangerous during their fast, though there is not specific data to back such speculation up. While the polar bear is master of its domain, human beings are, on the other hand, very poorly suited to it, and there is no doubt that out on the coverless, open ice we are at a huge disadvantage. In black and grizzly bear habitat, we can sometimes recourse to tree climbing or the use of cover or some other defensive option in the event of an encounter, but this does not apply to polar bear habitat.In a sense, this makes polar bears more dangerous than other bears relatively, rather than absolutely, and it demands that in their domain we exercise extreme vigilance.
For bear species in the temperate zone, the two most important issues are habitat loss and conflict with human beings. For the polar bear, these have less significance, although in recent times, oil and gas development has become a threat in some regions. Arguably, the greatest threat to polar bears is climate change, and specifically, global warming. While global warming is disputed in many of the temperate regions of the world, it is very hard to deny it in the polar regions. In the arctic, there is a lot of evidence of less and thinner ice, and of later freeze-ups and earlier thaws. Insufficient and weak ice will reduce the hunting potential of the polar bear and lead to an inadequate supply of food, which will mean less deposits of fat, leading to starvation. In the Hudson Bay and James Bay areas, this trend of later freezing and earlier thawing has reduced the feeding period for sows with cubs-of-the-year, by up to 25% of what it has been previously. This is a non-sustainable situation, and if it continues, these areas will cease to function as viable habitat, and the bears that presently live there will move north. For more information on this topic, go to the Issues section.
In the wilderness is the salvation of the world.
Henry David Thoreau