As sea ice melts, more and more polar bears can be found resting along Arctic coastlines. It is in these areas where their powerful sense of smell attracts them to garbage, stored food, dog teams and animal carcasses — bringing them into greater conflict with Arctic people.
Special Concern A wildlife species that may become threatened or endangered because of a combination of biological characteristics and identified threats. Polar bears have three sets of eyelids; the third helps protect their eyes from the glare of snow and ice.
Being at the top of the food web, polar bears can signal that there are problems in the Arctic marine ecosystem.
They are likely to be among the most significantly affected species as the Arctic warms and sea ice melts. Over thousands of years, polar bears have also been an important part of the cultures and economies of Arctic peoples. Polar bears depend on sea ice for their existence and are directly impacted by climate change , serving as an important indicator species.
As climate change continues to reduce the thickness of sea ice, the future of polar bears and their habitat are at risk. Less ice means increased conflict with humans as bears spend more time on land seeking new sources of food. The ice is the foundation of Arctic marine life, the ecosystem on which bears rely for every aspect of their lives.
It is where they mate and raise their cubs. Sea ice is also essential habitat for their primary food, ringed seals, as they pup and rest on the ice. Current knowledge shows that polar bears have some capacity to adjust to the warming Arctic, but the loss of sea-ice habitat may be happening too rapidly to allow for adaptation and there are no substitutes on land for the fat-rich seals on which the bears depend.
Some of the best-studied polar bear populations are spending more time on land, like those in Manitoba, Ontario and southern Nunavut. Polar bears live in one of the planet's coldest environments and depend on a thick coat of insulated fur, which covers a warming layer of fat.
Fur even grows on the bottom of their paws, which protects against cold surfaces and provides a good grip on ice. The bear's stark white coat provides camouflage in surrounding snow and ice. But under their fur, polar bears have black skin—the better to soak in the sun's warming rays.
These powerful predators typically prey on seals. In search of this quarry they frequent areas of shifting, cracking ice where seals may surface to breathe air. They also stalk ice edges and breathing holes. If the opportunity presents itself, polar bears will also consume carcasses, such as those of dead whales. These Arctic giants are the masters of their environment and have no natural enemies.
Females den by digging into deep snow drifts, which provide protection and insulation from the Arctic elements. They give birth in winter, usually to twins. Young cubs live with their mothers for some 28 months to learn the survival skills of the far north. Females aggressively protect their young, but receive no help from their solitary male mates.
In fact, male polar bears may even kill young of their species. Polar bears are attractive and appealing, but they are powerful predators that do not typically fear humans, which can make them dangerous.
Near human settlements, they often acquire a taste for garbage, bringing bears and humans into perilous proximity. All rights reserved. Is climate change affecting their population? Learn how polar bears have adapted to life on top of the world.
A polar bear photographed at Tulsa Zoo in Oklahoma. Polar bears depend on the sea ice, which forms above the open waters where their seal prey lives.
They will spend time on land when sea ice is not available and most pregnant polar bear females make their dens on shore near the coast. Polar bears are excellent swimmers, and they travel long distances between shore and the sea ice if necessary.
However, if a storm kicks up during these increasingly long swims caused by the warming ocean , they can drown. These long swims and storms are also often difficult for cubs. During periods of ice breakup, polar bears frequently swim between floating ice islands.
Unlike other bear species, polar bears are almost exclusively meat eaters carnivorous. They mainly eat ringed seals, but may also eat bearded seals. Polar bears hunt seals by waiting for them to come to the surface of sea ice to breathe. When the seal nears the surface, the polar bear will bite or grab the seal and pull it onto land to feed.
They also eat walruses and whale carcasses. Polar bears will search out bird eggs and other food sources, but none of these are abundant enough to sustain the large body mass and dense populations of polar bears.
Another vitally important food source in most areas are seal pups that are born and live in dens in the Arctic ice. The polar bear identifies these dens by smell and other markers and pounces though the roof of the den to capture the young seals.
In Hudson Bay, the availability of seal pups in the spring is increasingly limited by earlier melting of ice. In the Arctic, polar bears are at the top of the food chain; they eat everything and nothing except native hunters eats them. Polar bears tend to live solitary lives except when mating, when a female raising her cubs forms a family group, or when many bears are attracted to a food source like a beached whale. Young polar bears spending the summer ashore on the Hudson Bay coast will frequently play with each other, most commonly with their siblings.
Polar bears near Churchill on the coast of Hudson Bay are even known to play with chained sled dogs without killing them, which they could easily do. Polar bears breed in the late spring as the temperatures begin to rise in the Arctic. This is called delayed implantation and allows a female bear to physiologically assess her condition prior to starting gestation and the process of birthing, nursing, and carrying for her offspring for the next three years.
The period of actual gestation following implantation is only about 60 days. In the Hudson Bay population, where the reproductive biology of polar bears has been most extensively studied, it appears that a polar bear female carrying a blastocyst must achieve a body weight of at least pounds to have the blastocyst implant and start gestation.
If this threshold is not achieved, the blastocyst will reabsorb, the female will continue to hunt seals all winter, attempting to be fatter a year later and able to carry off a successful pregnancy.
In the beginning of the winter, a pregnant female will dig a den in a snow bank and begin the process of gestation. Depending on the area, pregnant females may enter dens anytime between early October and December.
The time of exit from dens occurs between late February and April. Most females dig their dens in a snow bank on land, but some also den on the floating sea ice. In Hudson Bay, females may dig a den in the ground instead, but they use areas where the snow will build up and provide insulation.
In the middle of winter in some of the coldest places on Earth, female polar bears give birth to cubs. Litter size is most commonly two cubs, but sometimes litters can be one, three, or, very rarely, four cubs.
Female polar bears in the Hudson Bay area spend remarkable periods of time fasting, the longest known of any mammal species. This fasting period before denning and in dens averages about to days. In Hudson Bay, pregnant females can successfully fast for as long as days.
The long period of fasting makes this species especially vulnerable to environmental changes like a warming climate, which reduces the amount of time they have available to build up the fat reserves they need to survive fasting and bring off a successful pregnancy.
When the cubs are born, they are completely dependent on their mother. Over the next two years, the cubs will learn from their mother how to catch seals themselves and to develop the other skills needed to survive and grow to adult size. Typically cubs will stay with their mother until they are two-and-a-half years old, but in some cases they will stay for a year more or a year less. If the mother is able to replenish her fat reserves sufficiently, she can produce a litter of cubs that survive until weaning every three years.
When food declines in abundance, there is a longer period between successive successful litters, and litter sizes are smaller. Polar bears in the wild can live to be 30 years of age, but this is rare. Most adults die before they reach 25 years. The conditions developing in Hudson Bay are such that females will no longer be able to birth and successfully raise a little of cubs.
When this happens, the adult bears will survive until they die of old age and the population will be doomed. Scientists are fearful that this pattern is also starting to happen in the more northern polar bear populations as the amount of Arctic ice continues to shrink.
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