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Thursidae - Ursus maritimus Edition

Give it up for the world’s largest living land carnivore!

The Polar Bear (Ursus maritimus) is born on land, but spends much of its time in the sea. It can be found exclusively in the Arctic Circle, and is very slightly bigger than its close relative, the Kodiak bear (a subspecies of Ursus arctos). The Inuit call the Polar Bear nanook, which is similar to the Yupik term nanuuk, and nanuq in the Inupiat language. The Inuit believed that the Polar Bear was nearly human and had the power to determine whether or not hunters would be successful. If the hunters were successful in killing a Polar Bear, it was because the bear had allowed itself to be killed, and the Inuit honored its spirit by showing respect and making offerings.

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Fossil records show that the Polar Bear began to diverge from Brown Bears during the Pleistocene, and evolved to fill a narrower ecological niche than its omnivorous cousin. Because of the remote nature of the Polar Bear’s habitat, making it difficult for humans to settle there in large numbers, the Polar Bear retains the most of its original range compared to all other extant carnivores. Adult male Polar Bears can weigh up to 1,540 pounds (700 kg) and measure up to almost 10 feet (3 meters) in total body length. Adult females are smaller, weighing up to 550 pounds (250 kg) and measuring almost 8 feet (2.4 meters) in length. The largest recorded Polar Bear was a male shot in Alaska in 1960. He weighed over a ton (2,209 pounds/1,002 kg) and stood just over 11 feet (3.4 meters) when stuffed and positioned on his hind feet.

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Of all bear species, the Polar Bear is the most carnivorous. It feeds primarily on seals, namely Ringed Seals and Bearded Seals. It’s rare for a Polar Bear to catch a seal either on land or in open water, but it is most successful when waiting in ambush at the holes in the ice the seals must keep open in order to breathe. Polar Bears have also been known to prey on whales, like narwhals and Beluga whales, as well as walruses, birds and their eggs. They will also scavenge carcasses, either the remains of other bears’ kills or large animals that died of natural causes, as pictured above. Polar Bears wash themselves in water or snow after feeding.

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Polar Bears are active year-round, with the exception of pregnant females. Pregnant females are able to fast for up to eight months, and even non-pregnant females and males can fast for a few months when necessary. Mating takes place during April and May, which is right around the time that the seals will start pupping. Fertilized eggs are not implanted until around September, at which time the active portion of gestation begins. Expectant females will dig maternity dens in the snow, give birth to one to three cubs around February, and emerge when the cubs have reached a weight of around 30 pounds (15 kg).

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Polar Bears are not very territorial and are relatively tolerant of each other. In general they prefer to avoid fighting when possible, but they have developed a reputation for being aggressive toward humans. Hungry bears are unpredictable and dangerous, and Polar Bears are generally unaccustomed to living close to humans and will stalk them as prey. At the same time, human-bear interactions in the Arctic are rare. Polar Bears can swim amazingly long distances for a land predator, with GPS tracking studies recording female Polar Bears swimming distances of 220 miles (354 km). It is not known whether this kind of endurance swimming is a relatively recent adaptation, because the polar ice has begun to decrease and the bears would not have had to swim such distances in the past. Polar Bears are considered to be a vulnerable species by the IUCN, and their greatest threat seems to be the effects of climate change.

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Source for all images used in this post.

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