When the San Diego Zoo got a call asking whether they could train a polar bear to walk on a treadmill, as Megan Owen remembers it, their first reaction was: Sure!
Owen is a biologist at the zoo, and her colleagues there regularly train polar bears in, let’s say, un-polar-bear-esque tasks. Their bears have learned to reach out their paws for voluntary blood draws. One female polar bear, Chinook, learned to lie still for ultrasounds. She was even part of a polar-bear hearing study in 2006, where she learned to press her nose on a pad when she heard a sound. “Polar bears are incredibly intelligent animals,” Owen says. It just takes patience and many, many buckets of raw meat and fish.
The call about treadmills came from Anthony Pagano, a biologist with the United States Geological Survey who wanted to study how polar bears walk. Once he persuaded two zoos to get on board—in San Diego and Oregon—Pagano had the polar bears. But he still needed a treadmill. He knew colleagues who had put other large mammals, such as mountain lions, on treadmills before. “But nothing as destructive as polar bears,” he says. Nothing as destructive, in other words, as a 500-pound colossus that could take out a human with a swipe of its paw.
Pagano’s team ended up buying a two-ton, 10-foot treadmill designed for racehorses. Then they brought it to the machine shop at Washington State University, which custom-built a bear-proof chamber of polycarbonate and steel. The enclosed chamber over the treadmill also allows researchers to sample the amount of air inside. As the bear walks, it starts using up some of the oxygen; this way scientists can get a sense of how much effort it is exerting.
Down in San Diego, the keepers decided that Tatqiq, a then-16-year-old female, would be the lucky bear. At first, Tatqiq’s keepers let her into the chamber with the treadmill off. She would lie or stand in there for a few minutes at a time and collect her food reward. Several weeks later, they turned the treadmill on at the slowest setting. “Of course the floor moves and that changes everything,” Owen says. Tatqiq headed for the exit.
But eventually, she was lured back with the promise of more food. Her trainers gradually turned the treadmill to higher speeds, still feeding her a scrap of meat or fish every 20 seconds. The whole training process took five months. In Oregon, where keepers trained another, 31-year-old female polar bear, it took eight months. “It takes a lot of patience,” Owen says.
What got Pagano interested in the giant-bear-proof-treadmill project is that polar bears are the largest mammals to walk on the soles of their feet. This is a stable method, but relatively inefficient at high speeds compared to, say, large cats that run on their toes, or horses that run on only the tips of their toes. From the treadmill experiments, the team found that the energetic cost of walking doubled when polar bears reached the not-exactly-blazing speed of 3.3 miles an hour. Go even faster, previous research suggests, and the bears are even less efficient.
Pagano had previously gone out onto the Arctic sea ice to study exactly how much polar bears are walking and running. Not very much at all, it turns out, at least not when they’re hunting. Polar bears usually hunt by perching near holes in the ice, waiting for an unlucky seal to come up for air. A bear might catch one seal a week. But as sea ice melts, polar bears are being pushed onto land, where they are forced to run after prey like flightless geese. And as the treadmill studies suggest, this running is energetically costly for polar bears.
The melting ice has also forced polar bears into the water more often. So Pagano, naturally, is also interested in the energetic cost of swimming. He persuaded his collaborators at the Oregon Zoo to install a motor for an endless pool. The next thing they did was train a polar bear to swim in it.