The polar bear (Ursus maritimus) is a hypercarnivorous bear whose native range lies largely within the Arctic Circle,
encompassing the Arctic Ocean, its surrounding seas and surrounding land
It is the largest extant bear species, as well as the largest extant land carnivore.
A boar (adult male) weighs around 350–700 kg (770–1,540 lb), while a sow (adult female) is about half that size.
Although it is the sister species of the brown bear,it has evolved to occupy a narrower ecological niche
, with many body characteristics adapted for cold temperatures, for moving across snow, ice and open water,
and for hunting seals, which make up most of its diet.[9] Although most polar bears are born on land,
they spend most of their time on the sea ice. Their scientific name means "maritime bear" and derives from this fact.
Polar bears hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present.
Because of their dependence on the sea ice, polar bears are classified as marine mammals.[10]
The polar bear is a marine mammal because it spends many months of the year at sea.
[46] However, it is the only living marine mammal with powerful,
large limbs and feet that allow them to cover kilometres on foot and run on land.
Its preferred habitat is the annual sea ice covering the waters over the continental shelf
and the Arctic inter-island archipelagos. These areas, known as the "Arctic ring of life",
have high biological productivity in comparison to the deep waters of the high Arctic.
The polar bear tends to frequent areas where sea ice meets water,
such as polynyas and leads (temporary stretches of open water in Arctic ice),
to hunt the seals that make up most of its diet.Freshwater is limited in these environments
because it is either locked up in snow or saline.
Polar bears are able to produce water through the metabolism of fats found in seal blubber,
and are therefore found primarily along the perimeter of the polar ice pack,
rather than in the Polar Basin close to the North Pole where the density of seals is low.[51]
The only other bear similar in size to the polar bear is the Kodiak bear,
which is a subspecies of brown bear.[52] Adult male polar bears weigh 350–700 kg (770–1,500 lb)
and measure 2.4–3 metres (7 ft 10 in–9 ft 10 in) in total length.[53] Around the Beaufort Sea, however,
mature males reportedly average 450 kg (1,000 lb).[54] Adult females are roughly half the size of males
and normally weigh 150–250 kg (330–550 lb), measuring 1.8–2.4 metres (5 ft 11 in–7 ft 10 in) in length.
Elsewhere, a slightly larger estimated average weight of 260 kg (570 lb) was claimed for adult females.
When pregnant, however, females can weigh as much as 500 kg (1,100 lb).
The polar bear is among the most sexually dimorphic of mammals, surpassed only by the pinnipeds such as elephant seals.[56]
The largest polar bear on record, reportedly weighing 1,002 kg (2,209 lb), was a male shot
at Kotzebue Sound in northwestern Alaska in 1960. This specimen, when mounted, stood 3.39 m (11 ft 1 in) tall on its hindlegs.
The shoulder height of an adult polar bear is 122 to 160 cm (4 ft 0 in to 5 ft 3 in).[57][58] While all bears are short-tailed,
the polar bear's tail is relatively the shortest amongst living bears, ranging from 7 to 13 cm (2.8 to 5.1 in) in length.[59]
