Polar bears on a treadmill: why scientists wanted to test their walking metabolism
Bears on treadmill
Scientists pull all sorts of stunts for the sake of research, including the latest, putting a polar bear on a treadmill in a new study looking at the animal's gait efficiency.
Polar bears are big and ferocious carnivores. They burn through more than 12,000 calories a day, and that's despite them just sitting around most of the time waiting for seals to surface from the sea ice.
But as climate change continues to melt that ice, the bears are forced to burn huge amounts of energy to get to any remaining ice. That got scientists including Dr.Terrie Williams, a Professor of Biology at the University of California, Santa Cruz, thinking about the efficiency of a polar bear's walk as it ambles across the Arctic, looking for food.
By figuring out how much energy they use while walking, they hope to get a sense of the energy these animals need just to stay alive.
To study the animal's gait, scientists trained polar bears borrowed from the Oregon Zoo and San Diego Zoo for eight months. They then constructed the treadmill used in the experiment by taking a treadmill previously used to train racehorses and added a big cage on top of it. (They made sure it was bear proof).
The training got off to a slow start. The polar bears were hesitant at first, but eventually got used to the environment. "That trick really is keeping the bears focused on a treadmill," says Williams. "We had a little snack box right in the front of the treadmill, and that kept their attention and they kept on walking."
After eight months, they were ready for the real rest. The trainers fitted the animal with a collar that measured its movement, and scientists measured its oxygen consumption once it started walking. Fresh air was being fed into the sealed-off treadmill cage, and an oxygen analyzer told the researchers the bear's metabolism from rest all the way to maximum speed.
Besides polar bears, scientists also put grizzly bears on the treadmill as a comparative species in the experiment.
"I found that the bears, when they're walking, they're darn efficient," says Williams. Polar bears, according to her, walk in a similar manner as a dog. Both animals have fairly straight legs, the only difference is that polar bears are flat-footed, like humans, and they walk at a fairly slow pace — around 3.4 kilometres per hour in the wild — which gives the appearance of a lazy gait.
But according to Williams, it doesn't matter whether an animal has a flat-footed or toe type of walk. At low speeds, they're both efficient. Just don't ask a polar bear to run, she jokes, because that will really cost them energetically.
Grizzly bears, on the other hand, have a dramatic gait. "Picture those big front arms that swing out, and the toes are pointed in and hit the ground with a great big paw."
"They're very different kinds of gaits," says Williams, referring to the two different bear species. "But interestingly enough, they turned out to have the same kind of efficiency and oxygen consumption."
The future of polar bears
That begs the question: if polar bears are not spending an excessive amount of energies walking, then why do they still require so many calories per day?
I think as humans, we're going to have to change our habits if we want polar bears.- Terrie Williams
According to Williams, that's because they consume a lot of energy just sitting around or standing at a level that's higher than many other mammals. That means they have a higher baseline requirement which translates to higher maintenance costs to run this bear engine, Williams explains.
In the current state of the Arctic, the polar bear's home, more and more ice is disappearing beneath their feet. "Polar bears are having a harder and harder time getting to the fatty seal resources that they typically feed on," says Williams, "and are having to move more to find things."
Some scientists think they will find a new source of food and feed on whale carcasses that get washed up on the ice, for example. But Williams isn't sure there'll be enough whale carcasses to sustain a population of polar bears.
"I think as humans, we're going to have to change our habits if we want polar bears," says Williams.