It’s been pretty cold here in the United States this past week. While I don’t mind the cold typically, it’s been a little too chilly lately! It’s a good time to channel my inner chionophile (an organism that can thrive in cold, snowy environments).
Today, let’s take a closer look at one of the most famous chionophiles out there: polar bears.
Polar bears (Ursus maritimus) are large bears living in the Arctic. Many people consider polar bears marine animals, as their range and lifestyle depend on sea ice. In fact, their scientific name literally translates to “maritime bear.” Polar bears prefer to spend their time on the frozen ice of the Arctic Ocean and will travel to remain on the ice as it melts and refreezes throughout the year. They even have slightly webbed feet to help them swim through the ocean. During the summer, polar bears spend their days on islands or coastlines with land ice, drift through the ocean on ice floes, or get stranded on warm land.
Besides their white fur, one of the most noticeable things about polar bears is their size. Polar bears are the largest land carnivore and the largest bear species in the world. Males are considerably larger than females: while the average female is 5.9 – 6.5 feet long (1.8 – 2 meters) and weighs 330 – 660 pounds (150 – 300 kilograms), males can reach 8.2 feet long (2.5 meters) and weigh between 660 and 1760 pounds (300 – 800 kilograms).
Made for the snow
Although the Arctic environment is harsh, polar bears have many adaptations to help them survive. Their footpads are covered in tiny bumps to provide traction on the ice. The fur between their toes provides extra insulation from the cold snow. An extremely thick layer of fat under their skin is fantastic insulation, helping keep the bear warm. This fat layer is 2 to 4 inches (5 to 10 centimeters) thick and can also serve as an energy resource when hunting is tough.
Polar bears also stay warm by having black skin. While polar bear cubs are born pink, their skin slowly turns black as they age. Even their tongues darken, although to a lesser extent. Some polar bears have blue tongues, while others have a more mottled tongue color. A polar bear’s black skin absorbs sunlight, helping to keep them warm in the cold.
But if polar bears are actually black, why do they look white? It all comes down to their fur: it’s hollow and clear. Polar bear fur looks white to us because of the way light is refracted in the clear hair strands. Polar bears may even “change” color based on fur oxidation or light conditions.
Hunting at sea
Contrary to what you might have seen in comics, polar bears do not eat penguins! Polar bears live in the Northern Hemisphere; penguins live in the Southern Hemisphere. If you see a penguin and a polar bear together in the wild, one is extremely lost!
Instead of hunting penguins, polar bears spend their time hunting seals. Polar bears will patiently wait at cracks in the sea ice or breathing holes to ambush seals coming up for air. To find these cracks in the ice, polar bears rely on their impressive sense of smell: they can smell a seal on the ice 20 miles (32 kilometers) away and even sniff out a breathing hole 1 mile (1.6 kilometers) away.
Ringed seals are a favorite prey species because they are the most numerous and provide many calories. The typical ringed seal provides a polar bear with enough energy for 11 days. To keep up a good layer of fat reserves, polar bears eat every four to five days.
Which brings up another interesting point: polar bears don’t hibernate! Males and non-pregnant females will spend the winter active and continuously hunting for food. However, pregnant females spend the winter in a den in the snow. This den provides a warm place to give birth and keeps the newborn cubs safe from the frigid cold: a den can be 38 degrees Fahrenheit warmer than the surrounding air. But even though they’re in a den, the pregnant females don’t go into true hibernation. Their metabolism and activity slow down, but the bears wake easily to care for their newborn cubs. These cubs quickly grow from just 1 pound to more than 20 pounds in a few months with help from their mother’s fat-rich milk. At 36% fat, a polar bear’s milk is the richest of any bear species.
After about two years of living with their mother, the polar bear cubs are independent enough to live the mostly solitary life of an adult on the ice.
Resources
Leave a Reply