Throughout all of the polar regions of the entire northern hemisphere roams the largest carnivorous quadruped alive in the world today, Ursus maritimus. More commonly known as the polar, this huge mammal is ruler of its domain by being well adapted to its environment.
The physical characteristics of polar bears make them a perfect fit in the arctic. They have a heavy stout body with strong muscular legs and well-adapted neck muscles. Their eyes are small and deep set to protect them against driving snow and cold wind. The bottoms of their feet are covered with fur for better traction on ice and they walk in a heel-toe manner. On land they can travel twenty-five miles per hour for short distances. They may not be as fast as their closest relatives, the brown bear, but this is the trade off for massive forelegs used to break through seal’s dens or to flip them out of the water.
Also in keeping with their carnivorous nature, polar bears have developed large stomachs with the capacity to hold 150 pounds of food. Their teeth are designed perfectly for eating meat. The canines are large and well developed which are used for catching and holding prey while the premolars are strong and sharp-edged for cutting and shearing the fat and blubber of seals. Of course these traits would be useless without the means to use them, and like most successful predators the polar bears has developed a good eyesight, excellent hearing, and a phenomenal sense of smell. Polar bears are capable of tracking seals form miles away if scents are carried to them by wind.
Although polar bears are really land animals, they are powerful swimmers. Ursus maritimus means “sea bear”. They can spend many hours in the sea and are capable of swimming great distances. They use a strong doggy-paddle stroke with their front feet, while the hind legs trail and act as rudders. By using this seemingly inefficient stroke, polar bears can attain speeds of six miles per hour, which can be maintained for up to sixty miles without a rest.
The polar bear’s principle diet is seals, particularly the ringed seal. They usually eat only the seal’s blubber and intestines, unless they are exceptionally hungry when they will devour the whole animal. Polar bears will kill a seal every few days if available, but are capable of going weeks between meals. The large stomach capacity is designed to allow them to take advantage of unexpected large meals that will help them survive the leaner times. During the summer months, when many bears are stranded on the land as the ice recedes northward, they turn to a variety of quite different foods in the absence of seals. Small mammals, birds and their eggs, or anything else that is edible is eaten.
Polar bears acute sense of smell plays a vital role in its hunting. During the spring when seal pups are born in chambers under the ice, bears wander over the ice fields in search of them. If a seal pup is found to be under the ice, by means of scent, the bear stomps down hard with its forefeet to break into the den. Polar bears also hunt grown seals on the ice. When a bear smells a seal t begins a careful and painstaking stalk, either over the land or through the water. When on land, it uses every available slope or ridges a cover and slowly creeps forward, eyes fixed on its quarry. To break up its outline against the snow the bear frequently lies flat on its belly. For a successful kill the bear needs to surprise the seal before it has time to slip into the water. When it gets approximately within one hundred feet of the seal the bear charges across the ground and seizes the seal killing it before it can escape. Polar bears also catch seals by waiting at their breathing holes in the ice. A seal may use several different breathing holes; therefore a bear may have to wait patiently for it to pop up at the right one. Then it pounces on the seal and quickly drags it out onto the ice to kill it.
Polar bears have a unique reproductive strategy that enables them to give birth in the arctic environment. The bears breed in April or May when they take time off from hunting seals. Shortly after conception, the female’s pregnancy grinds to a halt. The embryo, nothing more then a tiny hollow ball of cells the size of a pinhead floats inside the mother for four months or more. This process is called delayed implantation, which works in synchrony with the food supply. It allows a female to wait until after the important spring and summer seal-hunting periods before committing to the energetic demands of pregnancy. In July after all the sea ice has melted and all of the bears are left to fast on the shore, the female’s body will soon signal the fetus to resume development, if she has succeeded in building up enough fat reserves to sustain a pregnancy. Otherwise, the embryo will be reabsorbed with no ill effects to the mother.
The birth and nursing of the cubs takes place in a bear den built by the female. They are usually not much bigger then a phone booth, but function well by supplying them a warm safe haven. In this warm, protective environment the mother conserves energy and rations her crucial fat reserves by hibernating. During hibernation their heart rates can drop from as high as seventy beats per minute to as low as 8 beats per minute, their metabolism slows by fifty percent. Females do not eat, drink, urinate, or defecate while hibernating. Amazingly they give birth and nurse cubs while in this state of dormancy.
From mid November to December is when the bears give birth to their cubs, usually twins. Newborn cubs are very small, typically they weigh 1/400 of their mother’s weight. The cubs nurse every two to three hours about ten minutes at a time. Polar bear cubs can expect the richest milk of any of the bear species. It is thirty-five percent fat, richer than whipping cream. A drawback though is limited quantity. The fight for nursing rights is often lost by the runt of the litter who often dies due to starvation. The greatest threat to a cub’s survival is its mother’s waning milk supply as spring draws near.
The polar bear family finally breaks from the den by March. The mother bear who has not eaten in eight months loses an average of 280 pounds, forty-four percent of their autumn weight while the cubs have matured into twenty-two pound miniatures of their mother. The family spends the next few weeks around the den, sheltering in it at night as the mother recovers from hibernation. Meanwhile, the cubs turn the den into a playground as they play and wrestle while adjusting themselves to the life in the sun, wind and cold.
After this period of adjustment, females that gave birth inland must make a journey to the sealing grounds to eat. Following in their mother’s footsteps the cubs manage to keep up over towering ridges of jumbled ice and deep snow rifts. The female makes a few short stops to let her cubs snuggle up to her and suckle while they rest, but the drive to eat for the hungry females makes them complete the journey in as little time as possible. The arrival of the bears on the pack ice coincides with the birth season of their main prey, ringed seals. The mother leaves her cubs in a sheltered place as she goes in search of chambers under ice where seal pups lie. Cubs start to eat meat, as they grow larger, chewing on skin and blubber their mother brings from her seal kills. The cubs soon watch their mother catch seals out of breathing holes, or stalking them. They also learn how to swim, through a little encouragement.
Young polar bears stay with their mother for up to two years. During this time the cubs learn all the hunting skills they will need for survival on their own. Eventually when their education is complete, and the cubs are nearly full-grown, they begin to lead their own separate lives. At this time their mother will leave the cubs in order to mate again and start another family.
Currently it is estimated that there are between 20,000 to 40,000 polar bears. Canada has the largest population with approximately 15,000 bears living in the Canadian Arctic Archipelago and the Hudson Bay regions. The numbers of polar bears were in sharp decline for many years due to severe over hunting. In the 1950’s polar bear hunting from aircraft became a popular sport. They began to be hunted on a large and almost commercial scale, until the Soviet Union recognized that polar bears needed protection. In 1967, the “polar bear” nations: Norway, Russia, Greenland, United States, and Canada, signed an agreement to reduce the levels of hunting, giving polar bears protection. It is a great example of international cooperation in an attempt to conserve an animal species whose future survival is the shared responsibility of several different nations. Today, the polar bear population remains relatively stable. Whether these magnificent creatures will be allowed to roam freely over the drifting pack ice in the future largely depends on the human management of their unique habitat. It is up to everybody concerned to make sure that this remote part of the world remains as wild and unspoiled as possible, so that all its wildlife, including polar bears, can continue to live there in safety.