Polar bears (Ursus maritimus) are found in the arctic (polar) regions of the northern hemisphere, including the United States (Alaska), Canada, Russia, Norway, and Greenland -- today there are seven polar bear populations in these regions. Legislative efforts by "polar bear nations" to protect the polar bear from hunting were helping vitalize the species, but recent warming of the arctic, brought on by global warming, has emerged as a tremendous threat to the bears. Warming is causing earlier melts of the ice shelves on which polar bears hunt seals. With their hunting environment disapearing the species is becoming increasingly threatened and could be facing extinction. There are only 22,000 polar bears living in the wild today.
Polar bears are the direct descendants of the brown bear, evolving during the Pleistocene period when brown bears were isolated and separated by glaciers. In order to survive, northern bears underwent rapid evolutionary change to adapt to the arctic environment, including the development of a thick fur coat and four inches of blubber.
Polar Bear's Physical Characteristics:
Polar bears are large mammals. Males generally measure around 7.5 feet long (225 cm) and weigh between 1,200 and 1,800 pounds (550 to 800 kg). They have muscular legs and necks, a black nose, and relative to other bears, a small head and tail. Perhaps the most distinguishing physical feature of the polar bear is its extremely long neck, which they use to keep their head above water while swimming.
The polar bear is covered with a beautiful yellow/white coat of waterproof fur, which blends with their snowy environment to serve as camouflage while hunting. The coat consists of two layers -- an underlayer of short, fine white hair and an outer coat of longer hollow hairs, which improve insulation and increase buoyancy for swimming. With this thick coat, the polar bear is less likely to suffer from the winter cold than succumb to the summer heat.
The polar bear has black skin, which is thought to be a biological adaptation necessary for heat retention. Another adaptive feature is a very large stomach, which can hold more than 150 pounds (70 kg) of food. This comes in handy during hibernation periods, when the female polar bear can lose almost half her body weight. In addition, it allows polar bears to sometimes go weeks without significant amounts of food during the summer and early fall, after the ice melts, when they are stranded on land.
Polar Bear's Range:
Polar bears can be found in the extreme northern regions of Canada and Alaska as well as in the arctic regions of Russia, Norway, and Greenland. Canada maintains the largest population of polar bears (around 15,000) in the arctic archipelago and the Hudson Bay-James Bay regions.
Individual bears often cover significant ground in search of food and shelter -- over the course of their lifetime, they can travel up to 100,000 square miles (260,000 km). Polar bears are not particularly territorial, consequently, many bears can be found within a defined home range.
Polar Bear's Diet:
Given the scarcity of suitable arctic plant life, the polar bear has become the world's most carnivorous bear--almost its entire diet is meat-based. The polar bear's favorite food is seal, although it will also feed on fish, birds, dead sea animals (including whales), starfish, and algae.
As its latin name implies (ursus maritimus translates into "sea bear"), polar bears are very much at home in the water. In fact, they are known to sometimes embark on swimming expeditions lasting hundreds of miles, paddling at speeds of around 6 mph (10 kph). In addition, polar bears are excellent divers, capable of reaching depths of 15 feet (4.5 m) and remaining submerged for two or more minutes at a time. This enables them to effectively prey on marine life.
Polar Bear Reproduction:
Females come into heat every three years (starting at age four) from March to June and may mate with several males during this time. However, because of a fascinating process called "delayed implantation," (where the fertilized ovum remains in an arrested development stage in the uterus), the embryo will not begin developing until September. The pregnant female will then enter a hibernation den in October or November and given birth in either December or January.
The number of cubs delivered will range from one to four (average two per litter). They are born blind and hairless, and weigh only a couple of pounds. These cubs will feed on their mother's milk while she hibernates. By the time the mother is ready to leave the den in late March or early April, the cubs will weigh between 22- 33 pounds (10-15 kg).
The first years of a cub's life can be dangerous, with a real threat of starvation, disease or attack by other animals. During this period, the mother will teach her cub all of life's basics, including hunting and other survival techniques. By the time the cubs are two or three years old, they are left by the mother to fend for themselves.
Polar bears can live in the wild for twenty-five years or more.
Polar Bear Hibernation:
Pregnant female polar bears are generally the only polar bears that will hibernate, although in cases of extreme cold or heat, other polar bears will hibernate for short periods of time. In preparation for the hibernation period, they will try to put on enough fat to nourish themselves and their cubs for the winter.
The pregnant bear will build her own snow packed den, usually 6 to 10 feet (2-3 m) long. Snow serves as an excellent insulator, protecting the polar bear from the arctic winter.
During the hibernation period, polar bears will become completely inactive. Their heart rate will drop dramatically, and they will lose a tremendous amount of weight (up to 40% of body weight). After the female emerges from hibernation, with cubs in tow, she will return to the ice pack to feed her young.
Are polar bears dangerous?
Polar bears are considered by most biologists to be the most dangerous species of bear, although the grizzly is generally the most feared. Given the polar bears' remote location, they seldom come into contact with man, although there are recorded cases of bear attacks on Eskimos, who hunt the polar bear as a source of food and hide.
Polar Bear Social Interaction:
Polar bears are generally solitary animals, except during mating season and when mothers take care of cubs.
Polar Bear Conservation Efforts:
Polar bears are protected internationally under the 1973 International Agreement on the Conservation of Polar Bears and their Habitat. In addition, they are cared for under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), a treaty among more than 120 nations aimed at controlling illegal trade in endangered animal and plant species. In the United States, they are protected under the U.S. Endangered Species Act and the U.S. Marine Mammal Protection Act.
Global Warming and the Polar Bear (World Wildlife Fund):