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Science

Survival of the Biggest
by Margaret Etherton

 

Polar bears are titans. That means they are big—really big! The polar bear is so huge that you would think it would be easy to find, but it is so white that it is hidden in the snowy landscape. It is amazing that such a big animal lives in one of the coldest places on the planet. How do polar bears get to be so big, yet manage to survive in such a harsh place?

Polar bears are the largest carnivorous mammals on Earth. Carnivorous means they prefer to eat meat. Mammal means they have small babies that the mother feeds with her milk. And polar means they are only found inside the arctic regions at the North Pole.

The male polar bear can grow to be 800 kilograms (about 1800 pounds). He looks like a white, cuddly, furry, over-weight teddy bear. The female is quite a bit smaller—about half the size of her partner. They both have cute little ears and eyes, and a snout for sniffing.

All polar bears are nimble, running and leaping across the ice surprisingly fast. Even though they look big and clumsy, they are actually very graceful. They stream through the water using their front paws like huge paddles and their back legs like the rudder of a boat.

Polar bears must eat lots of meat for dinner to survive the cold. They can smell a breathing hole made in the ice by seals under a meter (about 3 feet) of snow and from a kilometer (about 0.6 miles) away. Sitting near the breathing hole for hours, they wait patiently for their dinner to come up for air. Ringed seals are their main diet, but they will also eat walrus, fish, narwhal, birds, and some small mammals.

The bigger polar bears are, the better they are at winning fights against other animals. In fact, they don't just catch and eat walruses—they fight them to the death. Winning fights means the strongest bears catch the most prey and can survive the harsh environment. The small, weak ones die out. This is called "survival of the fittest". Bigger, stronger, fatter polar bears produce more babies than the little piddly ones. Then their genes (that is, the blue print or plan of how they are going to look and grow) are carried on to the next generation of polar bears.

Polar bears are hard to see against the glary, white snow and ice. Why are they so white? Surprise—they are not white! Their hairs are hollow and transparent so that heat and light are caught and travel down to the skin. But polar bears look white because the hollow core of the hair reflects visible light. Their skin is actually black and absorbs heat from the sun to keep them warm. When the polar bear gets wet, its hairs stick together and help keep the water out like a waterproof coat.

Polar bears can live without eating during the summer months. When the ice over the bays melts, they can't catch their favourite food under the ice. Instead they live off their own blubber. This is called walking hibernation. In autumn, only female polar bears build dens in the snow, where they give birth to one or a litter of cute little cubs in winter. They lower their temperatures slightly and sleep. While sleeping, they can even feed their babies, but mother polar bears will wake up when they are disturbed.

Polar bears have grown so big to help them in the survival stakes. They are white against the snow. They are titans among animals. They throw their weight around and they are winners! It is a case of survival of the biggest.

Bibliography

Myers, Phillip. Mammals, An Explore your World Handbook. London: Discovery Books, 2000.
Macdonald, David, ed. The New Encyclopedia of Mammals. Oxford: Oxford University Press, 2001.
May, John and Michael Marten. The Book of Beasts. New York: Hamlyn Paperbacks, 1982.

Internet:

http://www.bears.org/animals/
http://www.biosbcc.net/ocean/marinesci/04benthon/arcplrbr.htm
http://animaldiversity.ummz.umich.edu/site/accounts/information/Ursus_maritimus.html