Tuesday, December 1, 2009

Polar Bear Diet Expansion with Climate Change

Nature is adaptable. If given time it can adjust, find new niches and new opportunities for survival. While rare, reports are coming in of Polar Bears eating Caribou, Lemmings and Ravens. As the polar ice melts, new species are becoming available as a food source. Harbor Seals are moving in to occupy the shores of Hudson Bay. Polar Bears are finding new sources of food and are being less finicky in what they eat... it's a good thing... right?

Not so much.

I have always assumed that Polar Bears are strict carnivores. All of the documents say that their main food source is the Ringed Seal. It made sense that they are opportunistic and will take advantage of any meal they can find but it didn't occur to me that they would only eat certain parts of the seal. In speaking with the naturalists and scientists associated with Polar Bears International (PBI), I learned that Polar Bears are lipovores.

The Ringed Seal (Pusa hispida) utilizes a thick layer of blubber to keep it warm on the ice floes of the arctic. This fat layer is what the Polar Bear needs to build body mass for it's summer long fast. In most cases, the bear will not eat the meat! I thought they would eat every morsel, taking advantage of every opportunity. I was shocked but suddenly it made sense as to why the arctic fox would follow the bear onto the ice. Why hunt for your own food when all you need to do is wait for someone else to capture it for you?

As it turns out, Polar Bears, in addition to calories, obtain much of their water from the fat of the Ringed Seal. If the bear begins to eat protein they need to take in a higher amount of water from outside sources. Have you ever tried to get a cup of water from snow? Ten inches of fresh snow can contain as little as 0.10 inches of water! It takes 1 calorie to warm 1cc of water 1 degree centigrade. Since temperatures can get as low as -68 C... well... after a lot of math you can see it takes quite a bit of effort to get very little reward.

All of this is leading to more energy expenditure to receive a far smaller amount of benefit and in some cases, a negative benefit or at best no benefit at all. The Harbor Seal (Phoca vitulina) births on shore, not the ice so they have a thinner fat layer than the Ringed Seal. Have you ever seen a Lemming? Not much bigger than the hamster you had as a kid. And Caribou is exceptionally lean meat, great protein but not much water.

Moral of the story? It takes time to adapt, change is happening too quickly, we need to slow it down as much as we can to give these animals a fighting chance. Get involved.


John W. Wall said...

Great series you have going here, Rebecca.

Mark said...

I am also enjoying this series. I have been wondering how the bears will be adapting to their changing environment. Thanks so much for the info.

Viagra Online said...

What an awesome nature fact!
I can't understand why if nature is so perfect, then We came up with some inventions which are breaking down the earth balance.

Anyway, I just wanted to congratulate you for doing such a piece of informative work