polar bear

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[edit] Natural range
The polar bear is a circumpolar species sometimes regarded by authorities as a marine mammal[1] found in and around the Arctic Ocean whose southern range limits are determined by pack ice (their southernmost point is James Bay in Canada). While their numbers thin north of 88 degrees, there is evidence of polar bears all the way across the Arctic. Population estimates are generally just over 20,000.[2]

Their main population centers are:

Wrangel Island and western Alaska
Northern Alaska
Canadian Arctic archipelago
Greenland
Svalbard-Franz Josef Land
North-Central Siberia
Their range is limited by the availability of sea ice that they use as a platform to hunt seals, the mainstay of their diet. The destruction of its habitat on the Arctic ice, which has been attributed to global warming, threatens the bear's survival as a species; it may become extinct within the century. Signs of this have already been observed at the southern edges of its range.[3] [4]


Polar bear sow and two cubs on Beaufort Sea coast, Alaska
[edit] Size and weight
The largest extant species of land carnivore, a male polar bear can be twice the weight of a Siberian tiger. Most adult males weigh from 300 to 600 kg (660 to 1300 lb) and measure 2.4 to 2.6 m (7.9 to 8.5 ft) in length. The largest polar bear ever on record was a bear shot in Kotzebue Sound, Alaska in 1960. [5] According to Guinness World Records 2006, this colossus weighed an estimated 880 kg, or 1960 lbs, and, mounted, it was 3.38 m (11 ft 11 in) tall. Adult females are generally about half the size of males and normally weigh 190 to 300 kg (420 to 650 lb). They typically measure 1.9 to 2.1 m (6.25 to 7 ft). At birth, cubs weigh 600 to 700 g.

A 2004 National Geographic study showed that polar bears that year weighed, on average, fifteen per cent less than they had in the 1970s.[4]


[edit] Subspecies
It is generally believed that there are no living polar bear subspecies.[6] In fact, because polar bears bred with brown bears have produced fertile hybrids,[7] [8] it can be argued that polar bears are a subspecies of brown bear.

The number of distinct populations depends on who is counting. The IUCN/SSC Polar Bear Specialist Group ("PBSG"), the preeminent international scientific body for research and management relating to polar bears, currently recognizes twenty populations, or stocks, worldwide.[9] Other scientists recognize six distinct populations, but no (living) subspecies:[10]

Chukchi Sea population on Wrangel Island and western Alaska
Northern and northwestern Alaska and northwestern Canada (the Beaufort Sea population)
Canadian Arctic archipelago
Greenland
Spitzbergen-Franz Josef Land
Central Siberia
Other sources list these subspecies:

Ursus maritimus maritimus[11]
Ursus maritimus marinus[12]

[edit] Fur and skin

Video:http://www.youtube.com/results?search_query=polar+bear&search=Search
picture;http://hk.search.yahoo.com/search/images?p=polar+bear&fr=FP-tab-img-t&ei=UTF-8&meta=rst%3Dhk
北極熊的住處

北極熊只住在遙遠的北極地區，那兒非常寒冷，到處都覆蓋著冰和雪。所以只有在加拿大、美國阿拉斯加、挪威的冷岸群島、俄羅斯和丹麥的格陵蘭島才能看到北極熊。

北極熊的身體

一隻成年的北極熊體重約有六百五公斤，體長約有三公尺。除了鼻子和腳墊外全身長滿了又濃又密的白毛。牠們的表皮還有一層脂肪，可以禦寒。

北極熊在陸地上移動的方法很特別﹕牠們可以用溜冰的方式前進，也可用滑雪的方法，以前腳當雪橇，用後腳來推動身體。牠們游泳時，前腳用狗仔式的方法撥水，後腳就拖在身後當做舵來用，而且還可長時間停留在水中。



北極熊的食物

北極熊的主食是海豹，通常只吃牠們的脂肪層和腸子。但北極熊也是食腐動物，故也吃海象、白鯨和北極鯨的殘骸。到了夏天，牠們被困在陸地上時，則以鳥類、鳥蛋和植物為食糧。

北極熊的求偶和交配

母熊長到五、六歲大才有生育能力，直到二十多歲為止。熊寶寶在兩歲多之前都會在媽媽身邊，所以母熊每隔三年才會生育。母熊準備要交配時，尿液裡會散發出一種特殊的氣味，公熊就靠著這氣味找到母熊。

交配行為通常在四月或五月進行。交配完幾個月後，受精卵才會在子宮裡著床，這種懷孕方法稱為

在youtube打 polar

bear 可以watch videos