Bears that don't hibernate may become extinct by the end of this century...

Polar bears are one of the most iconic animals on our planet and the world's largest terrestrial carnivores. Although born on land, they spend most of their time on sea ice and are therefore classified as marine mammals . The polar bear's scientific name, Ursus maritimus, is also explained based on the polar bear's native habitat and means " sea bear " in Latin.

Image source: arctic kingdom

About 400,000 years ago, polar bears diverged from brown bears in Svalbard and adapted to the unique ecological environment of the high altitudes of the Far North in a very short period of time (compared to the time it takes for species to evolve).

From now on, their outer hair is hollow and can reflect light, making the fur look white, which helps polar bears camouflage on the ice field, but in fact the skin under their hair is black , which we can glimpse from the exposed nose, and under the skin, a layer of fat about 12 cm thick serves as an excellent "thermal suit" for polar bears to move in the polar regions.

Image source: Dept. of Fish and Wildlife

In addition, polar bears have "broken" the fine tradition of their bear ancestors: they no longer build nests for hibernation.

When winter comes, brown bears can find almost nothing to eat in the wild, so they can only build dens to hibernate. In contrast, polar bears have plenty of food in winter , so they don't need to build dens.

The only exception is pregnant females, who must build dens so that their newborn polar bear cubs can be born in a warm environment, otherwise the cubs will freeze to death in the severe cold of the Far North.

Polar bear cubs usually need to nurse for two and a half years after birth.

Image source: wikipedia

Polar bear on sea ice

Seals are the main food source for polar bears, and most of them live in areas with a lot of sea ice. They like to lie on the sea ice to rest and bask in the sun, so the main activity area of ​​polar bears is also on the sea ice.

Image credit: Thomas Johansen / NASA

Whenever autumn comes in the Northern Hemisphere, temporary ice caps of varying sizes will form on the sea surface of the Arctic Circle. At this time, polar bears will use their extremely sensitive sense of smell to search for areas where seals appear and ambush on the sea ice in advance . When they observe seals coming up the sea ice, polar bears are not in a hurry to take action, but will wait until the seals move closer to the center area before taking action. At this time, it takes a long time for the seals to reach the edge of the sea ice, and it is difficult for them to escape from the polar bears' pursuit.

After entering winter, as the daylight hours become shorter, seals have little interest in moving on the sea ice, and polar bears have fewer opportunities to hunt. However, they are very clear about the habits of their prey. Although seals can swim underwater, they have to surface to breathe after a few hours. Therefore, polar bears will quietly squat beside the hole in the sea ice. When a seal shows its head at the hole, the polar bears will quickly extend their claws and hit the seal on the head. At the same time, they will rush up to bite the seal's body and drag it to a safe place on the ice to enjoy it.

Image source: reddit

Typically, after a hunting season, an adult polar bear can weigh up to 50% more than a few months ago . This extra weight is mostly accumulated fat to help them survive the 3-6 month fasting period.

However, with the impact of climate change (such as rising temperatures), sea ice forms later in the fall, about three weeks later than 20 years ago, while the spring ice melts earlier. As a result, polar bears' fasting period becomes longer and longer , their bodies become thinner, and they have fewer cubs.

A hungry polar bear

Image credit: Andreas Weith

There is also a realistic problem facing polar bears at this time. As the sea ice retreats, the sea ice observed in the Arctic is getting farther and farther away from the coast, which means that polar bears have to swim farther to reach the sea ice.

Although polar bears are good swimmers, they are not good at diving , which is why they cannot go directly into the water to hunt seals. At the same time, swimming consumes five times more energy than walking the same distance on land at the same speed. Therefore, long-distance swimming is very risky. If a polar bear's energy reserves are exhausted, it may die from hypothermia or drowning.

Polar bear swimming towards sea ice

Image source: arctic kingdom

How zoos protect polar bears

Polar bears are already on top of the world, and if the sea ice disappears, they will have nowhere to go.

In view of the increasingly severe living environment of polar bears in the wild, some Arctic biologists believe that if climate problems are not improved, polar bears may become extinct in the wild by the end of the 21st century.

Therefore, scientists are also trying to prevent this from happening. In addition to protecting polar bears in the wild, polar bears can also be artificially fed and bred in zoos. For example, the polar bear pavilion in the Beijing Zoo uses modern technology to build living facilities such as ice beds, sprays, air conditioners, and swimming pools for polar bears. In the hot season, they also prepare corresponding heatstroke prevention and cooling measures for polar bears.

Beijing Zoo prepares ice beds for polar bears

Image source: Beijing Zoo Weibo

However, polar bears in zoos have lost the vast ice fields, and some people believe that captive polar bears are not doing well. But the role of modern zoos is no longer simply to display and feed them. They design exhibits and interactions to keep polar bears curious and involved. At the same time, they also provide data for many research projects to protect polar bears, which helps researchers better protect wild polar bears.

Therefore, many bases, including zoos, have made great contributions to the protection of polar bears, allowing their counterparts in the wild to continue roaming on the sea ice.

References:

1.polulation genomics reveal recent speciation and repid evolutionary adaptation in polar bears

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4089990/

2.Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2841953/

3.A Clever Population of Polar Bears Survives on Glacial Ice in Greenland

https://www.smithsonianmag.com/smart-news/a-clever-population-of-polar-bears-survives-on-glacial-ice-in-greenland-180980280/

4.Aquatic behavior of polar bears (Ursus maritimus) in an increasingly ice-free Arctic

https://doi.org/10.1038/s41598-018-27947-4

Author: Fish

Winner of the Silver Award for Outstanding Science Popularization Works of China Science Writers Association

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