Lord of the Arctic
The polar bear is the largest carnivore on Earth. A big male bear can weigh more than 700 kilos! Polar bears mainly hunt on the ice pack, killing seals when they come up to the surface to breathe. But they also spend time on shore, where they eat eggs, plants and even rubbish thrown away by humans. The polar bear is right at the top of the oceanic food chain; indeed it is often classed as a marine mammal.
Remarkably well adapted
Underneath its usually immaculate white fur coat that helps it blend into the landscape, the polar bear has a layer of fat that protects it from the cold and serves as a reserve of energy when prey is scarce. The bear’s skin is black, which absorbs the heat that is channelled inwards by the strands of white fur, and the it has stubby ears that reduce its heat loss. Lastly, the polar bear has wide paws that spread like snow shows and stop it sinking too deep into the snow.
An animal with almost no predators
The polar bear has no predators except Man, so it is lord of all it surveys. Bears are naturally curious and will explore anything that seems new, but once its curiosity is satisfied, a bear will usually go away. Although it looks like a great big teddy bear, the polar bear can be a very dangerous animal, but it is a protected species and cannot be killed except to protect human life.
An eternal wanderer
Polar bears are at home both on land and in the water. Males lead a solitary existence and usually occupy a vast expanse of territory. The females are more sedentary, digging a den in the snow where they fast all winter and give birth to their cubs. The cubs, which are born deaf, blind and without fur, stay for two years with their mother. Only 60% of them will reach adulthood.
The polar bear’s ancestors
Scientists have never found any fossils of polar bears (Ursus maritimus) so the species is probably quite recent. Their ancestors, some 200,000 years ago, were brown bears that adapted to a coastal milieu and learned to hunt seals.
A diet balance that depends on the seasons
From March to June, polar bears hunt seals on the ice pack. They eat up to 40 kilos of food per day, mostly fat, and can store up to 26 cm of fat under their skin. When the pack ice melts in summer, food becomes scarce. Male bears can live for about 6 months without eating. Over winter, female bears spend 7-8 months in their dens in the snow, suckling their cubs, and during that time they have no food intake.
Gestation programmed to wait for spring
Polar bears mate in April-May. Once the female’s ovule is fertilized, the growth/maturity process is “suspended” until September-October: the mother-to-be then seeks out a zone where there is abundant snow and digs a den where she will spend the winter. Bear cubs are usually born in December and are suckled in the snow den until spring. This delay programmed into the bear’s ovules means that the cubs to discover the outside world during the most suitable season in terms of food availability and weather conditions.
Polar bears: playful and curious
Curious polar bears have been known to go into houses, to climb on boats and to try to get aboard buses. Bear cubs have been seen sliding down snow drifts on their buttocks, chasing birds and playing with the wind. All of which may be ways to learn to solve new problems; the ability to adapt is probably an indispensable survival skill in the polar bear’s extreme environment.
Of bears and men
Churchill is the northernmost town in Canada before the Arctic wilderness. By the end of the autumn, the town can be invaded by up to 60 polar bears, attracted by the prospect of scavenging food in the town’s rubbish dump. The townspeople try to scare them away so that the bears do not forget how to find food in their natural milieu. The food that they find in towns is very different to what they hunt in their natural habitat, and little is known about the impact that a change of diet could have on the bears.
At the top of the marine food change: toxic waste generated by Man
DDT, PCBs, hydrocarbons, heavy metals, radio-active substances… the polar bear is at the top of the food chain and ends up with all its preys’ pollutants in its fat layers. Not just pollutants from local mining and petroleum operations but also pollutants that have been washed down by rivers and brought to the Arctic by ocean currents and the winds.
Notice: protected species
The first International conference on polar bears was held in Alaska in 1965. Well after the “romantic” era of the trappers, bear hunters continued to kill hundreds of polar bears a year (a single hunter with special bait rifles could kill up to a hundred every season). Veritable “Arctic safaris” using boats, planes and helicopters were organised right up until the mid-1960s.
Today, an international agreement (with provision for some hunting by local native peoples where relevant) protects both the polar bears and their habitat. As a result, the number of animals in the Arctic has increased from 5,000 to 20,000. However, the combination of pollutants and the shrinking (now a recognized fact) of the pack ice that is their hunting ground could well mean that the days of the polar bear are numbered.