May 29, 2010

Polar Bear (Ursus maritimus)

Life is hard in the arctic. In the winter, temperatures can drop to 50 degrees below zero and fierce, howling winds are common. And forget about the sun...it goes down in October and doesn't come up again until March. For all appearances, it seems to be a snow and ice covered wasteland. Sure, the Northern Lights are pretty, but that is small consolation when you can't find any food and you are freezing your buns off. What could possibly live in such a place?

The answer is, actually, quite a lot. Many creatures (and some humans) have adapted beautifully to life in the frozen tundra and call the top of the world home. And one of these creatures just happens to be the largest land predator in the world today...the polar bear.


The polar bear has been given many names over the years. The Norse (as in, Vikings) referred to the polar bear as "the rider of the icebergs", "the sailor of the floe", "the whale's bane", "the seal's dread" (for good reason!), and even "white sea deer"...a particularly creative name; apparently, the mead was flowing freely on those long winter nights. They said the bear had "the strength of 12 men and the wit of 11".


The Sami people in the Lapland region of Norway won't even speak the polar bear's name, for fear of offending it. Instead, they refer to the bear as "God's dog" or "old man in a fur coat".


The Latin name for the polar bear is Ursus maritimus, which literally means "sea bear". That is a good name for this bear, because he loves to swim. Polar bears can swim for 60 miles without rest, and they can dive to 15 feet. They use their massive front paws as giant paddles to push themselves forward in the water, and they use their hind paws as rudders. He is very good in the water because he spends most of his time going from ice floe to ice floe, looking for his favorite food...ringed seals.


Polar bears just
love a ringed seal. It is by far the most common item on the menu, although they will also hunt walruses and even small whales on occasion. Seals, being just slightly more bite-size than a walrus or whale, would seem to be the easier prey. Hunting seals in the arctic, however, is not quite that easy. It takes intelligence, strength, and lots of patience. Luckily, our polar bear friend is equipped for the job. Polar bears hunt seals by finding a breathing hole in the ice and waiting by it, ready to ambush the unlucky seal who comes up for some fresh air. Seals need to come up every 5 to 15 minutes to breathe; the problem is that these seal-made breathing holes are all over the place, and the chances that a seal will come up through this particular breathing hole can be mighty slim. A bear can end up waiting at a breathing hole for hours...or even days.

That's okay, because polar bears can go for weeks without food if they have to. They don't hibernate like other bears do, but when food is scarce, they can go into a state called "walking hibernation" in which their metabolism slows way down.


But when food is plentiful, they make use of it. These guys can eat! They have huge stomachs and can eat 100 pounds of yummy seal in one sitting. Despite being such a ravenous carnivore, however, their table manners are actually rather nice (for a ravenous carnivore, that is). A polar bear will actually share his meal with other polar bears...as long as they ask him nicely first. What is asking nicely in polar bear speak, you ask? Well, guests to the dinner table basically have to beg. Begging consists of approaching in a very submissive manner, crouching low to the ground, then circling around the carcass slowly, and then touching noses...ever so gently...with the big bear in charge. If a bear does this right, he is allowed to join the meal. Large groups of polar bears have been observed peacefully sharing a big whale or walrus kill together.


Polar bears are big...very big. Males can weigh up to 1,500 pounds and females can weigh up to 550 pounds. They are extremely strong and have thick, curved claws that measure more than two inches long. All of this comes in handy when your only source of food consists 150 pound seals or 2,000 pound walruses and 4,000 pound whales.


Living in such an extreme environment means having to find ways to adapt and deal with the special challenges that a habitat like the arctic presents...and polar bears are no exception. They have some amazing adaptations to life on the ice. Their fur, for example, is very dense and well insulating and covers skin that is actually black (all the better to trap heat from the sun). Their fur is actually not white, but rather transparent...it reflects light in much the same way that ice does. The translucent fur and black skin cover a 4 1/2 inch thick layer of blubber that also helps keep in the heat. In fact, polar bears are so good at keeping warm that they actually overheat when they run!

They have huge feet...up to 12 inches across...that help them walk on ice and paddle in the water. They have longer necks than other bears, which is helpful when poking around in holes in thick ice, looking for seals.

And all those cute cartoons you've seen of polar bears and penguins playing together? Well, you can forget it. Polar bears and penguins live on opposite ends of the earth and never come into contact with each other. Polar bears are exclusively in the northern hemisphere, and penguins are in the southern hemisphere. A good way to remember this is by simply understanding what the terms "arctic" and "antarctic" mean. "Arctic" comes from the Greek word for "bear", and "antarctic" is Greek for "without bear". Easy, huh?

Polar bears are being talked about a lot in the news now because of global warming, but what exactly does that mean? Why is climate change such a threat to polar bears? Well, it all has to do with ice. Ice is a must for polar bears. They depend on it for their survival. Predators go where their food goes, and in the case of the polar bear, that is the arctic ice. Seals, walruses, and whales are all marine mammals and spend most or all of their time in the ocean. Polar bears are great swimmers, but they are no match for a seal in open water. The only access a hungry polar bear has to his food is where the ice meets the ocean. Polar bears follow the ice floes, sometimes swimming for miles to reach the next floe in search of seals. As this ice melts, the bears have to swim farther and farther to find suitable hunting grounds. As a result, many bears starve to death or simply die from exhaustion or drowning because the swimming distance has become too great.

The arctic is experiencing the warmest climate in four centuries. The rapid shrinking of the sea ice is making it harder and harder for polar bears to make a living. They are superbly adapted to life in their arctic environment, but now that environment is changing, and the changes are happening too fast for the polar bear to adjust. Less ice means that the polar bears can't reach their prey, and shorter hunting seasons means more chance for starvation and population decline.
The polar bear is an amazing animal, but one that is in danger. His way of life is quickly becoming a thing of the past. His habitat is literally disappearing beneath his feet. Hardly a fitting treatment for "God's dog"...


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