Tuesday, November 6, 2012

Among young males in particular

Among young males in particular, play-fighting may be a means of practicing for serious competition during mating seasons later in life.[70] Polar bears have a wide range of vocalisations, including bellows, roars, growls, chuffs and purrs.In 1992, a photographer near Churchill took a now widely circulated set of photographs of a polar bear playing with aCanadian Eskimo Dog a tenth of its size. HP Compaq HSTNN-LB51 Battery

The pair wrestled harmlessly together each afternoon for ten days in a row for no apparent reason, although the bear may have been trying to demonstrate its friendliness in the hope of sharing the kennel's food.[72] This kind of social interaction is uncommon; it is far more typical for polar bears to behave aggressively towards dogs.

Courtship and mating take place on the sea ice in April and May, when polar bears congregate in the best seal hunting areas.[74] HP Compaq HSTNN-LB52 Battery

A male may follow the tracks of a breeding female for 100 km (62 mi) or more, and after finding her engage in intense fighting with other males over mating rights, fights which often result in scars and broken teeth.[74] Polar bears have a generally polygynous mating system; recent genetic testing of mothers and cubs, however, has uncovered cases of litters in which cubs have different fathers.[75] HP Compaq HSTNN-MB05 Battery

Partners stay together and mate repeatedly for an entire week; the mating ritual induces ovulation in the female.[76]

After mating, the fertilized egg remains in a suspended state until August or September. During these four months, the pregnant female eats prodigious amounts of food, gaining at least 200 kg (440 lb) and often more than doubling her body weight. HP Compaq HSTNN-OB06 Battery

When the ice floes break up in the fall, ending the possibility of hunting, each pregnant female digs a maternity den consisting of a narrow entrance tunnel leading to one to three chambers.[74] Most maternity dens are in snowdrifts, but may also be made underground in permafrost if it is not sufficiently cold yet for snow.[74] HP Compaq HSTNN-OB52 Battery

In most subpopulations, maternity dens are situated on land a few kilometers from the coast, and the individuals in a subpopulation tend to reuse the same denning areas each year.[27] The polar bears that do not den on land make their dens on the sea ice. In the den, she enters a dormant state similar to hibernation. This hibernation-like state does not consist of continuous sleeping; however, the bear's heart rate slows from 46 to 27 beats per minute.[77] HP Compaq HSTNN-OB62 Battery

Her body temperature does not decrease during this period as it would for a typical mammal in hibernation.[45][78]

Between November and February, cubs are born blind, covered with a light down fur, and weighing less than 0.9 kg (2.0 lb),[76] but in captivity they might be delivered in the earlier months. The earliest recorded birth of polar bears in captivity was on 11 October 2011 in the Toronto Zoo.[79] HP Compaq HSTNN-UB05 Battery

On average, each litter has two cubs.[74] The family remains in the den until mid-February to mid-April, with the mother maintaining her fast while nursing her cubs on a fat-rich milk.[74] By the time the mother breaks open the entrance to the den, her cubs weigh about 10 to 15 kilograms (22 to 33 lb).[74] For about 12 to 15 days, the family spends time outside the den while remaining in its vicinity, HP Compaq HSTNN-UB11 Battery

the mother grazing on vegetation while the cubs become used to walking and playing.[74] Then they begin the long walk from the denning area to the sea ice, where the mother can once again catch seals.[74] Depending on the timing of ice-floe breakup in the fall, she may have fasted for up to eight months.Cubs may fall prey to wolves or to starvation. Female polar bears are noted for both their affection towards their offspring, and their valiance in protecting them.HP Compaq HSTNN-UB18 Battery

One case of adoption of a wild cub has been confirmed by genetic testing.[75] Adult male bears occasionally kill and eat polar bear cubs,[80] for reasons that are unclear.[81] As of 2006, in Alaska, 42% of cubs now reach 12 months of age, down from 65% 15 years ago.[82] HP Compaq HSTNN-UB68 Battery

In most areas, cubs are weaned at two and a half years of age,[74] when the mother chases them away or abandons them. The western coast of Hudson Bay is unusual in that its female polar bears sometimes wean their cubs at only one and a half years.[74] This was the case for 40% of cubs there in the early 1980s; however by the 1990s, fewer than 20% of cubs were weaned this young.[83] HP Compaq HSTNN-UB69 Battery

After the mother leaves, sibling cubs sometimes travel and share food together for weeks or months.[61]

Females begin to breed at the age of four years in most areas, and five years in the Beaufort Sea area.[74] Males usually reach sexual maturity at six years; however, as competition for females is fierce, many do not breed until the age of eight or ten.[74] HP Compaq HSTNN-W42C Battery

A study in Hudson Bay indicated that both the reproductive success and the maternal weight of females peaked in their mid-teens.[84]

Polar bears appear to be less affected by infectious diseases and parasites than most terrestrial mammals.[81] Polar bears are especially susceptible toTrichinella, a parasitic roundworm they contract through cannibalism,[85] HP Compaq HSTNN-W42C-A Battery

although infections are usually not fatal.[81] Only one case of a polar bear withrabies has been documented, even though polar bears frequently interact with Arctic foxes, which often carry rabies.[81] Bacterial Leptospirosis andMorbillivirus have been recorded. Polar bears sometimes have problems with various skin diseases which may be caused by mites or other parasites. HP Compaq HSTNN-W42C-B Battery

Polar bears rarely live beyond 25 years.[86] The oldest wild bears on record died at age 32, whereas the oldest captive was a female who died in 1991, age 43.[87] The causes of death in wild adult polar bears are poorly understood, as carcasses are rarely found in the species's frigid habitat.[81] In the wild, old polar bears eventually become too weak to catch food, HP Compaq HSTNN-XB0E Battery

and gradually starve to death. Polar bears injured in fights or accidents may either die from their injuries or become unable to hunt effectively, leading to starvation.[81]

The polar bear is the apex predator within its range. Several animal species, particularly Arctic Foxes and Glaucous Gulls, routinely scavenge polar bear kills.[52] HP Compaq HSTNN-XB11 Battery

The relationship between ringed seals and polar bears is so close that the abundance of ringed seals in some areas appears to regulate the density of polar bears, while polar bear predation in turn regulates density and reproductive success of ringed seals.[56] The evolutionary pressure of polar bear predation on seals probably accounts for some significant differences between Arctic and Antarctic seals. HP Compaq HSTNN-XB18 Battery

No comments:

Post a Comment