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Watch grizzly bears run on treadmills—and find out why they like hiking trails

If you’ve ever worried a bear might be after your picnic basket, you may want to take the hardest, hilliest trail to your destination. That’s the take-home message of a new study, in which researchers got nine bears to run on treadmills—a first for science—and found that they, like their laziest human counterparts, prefer flat paths to save energy. The study, scientists say, may help explain why bears are often found around popular hiking trails.

Grizzly bears (Ursus arctos horribilis) need to stock up on energy before they slip into winter hibernation. As opportunistic omnivores, they eat just about anything—berries, roots, grass, insects, and meat—to put on weight. That requires a lot of foraging, but what paths they pick while looking for food was a mystery. “This study does for bears what Fitbit and other fitness trackers have done for people,” says Scott Nielsen, a conservation biologist at the University of Alberta, Edmonton, who was not involved in the study.

To find out how grizzly bears spend their energy while searching for food, researchers at Washington State University’s Bear Research, Education, and Conservation Center placed a treadmill in a custommade, sealed enclosure, built with steel frames and polycarbonate sheets to make them air-tight. Then, they trained nine captive bears to walk and run on the treadmill at various slopes, both uphill and downhill.

Training the bears was no easy task. Before beginning their experiments, the researchers acclimatized the bears to the treadmill enclosure over 2 months, using generous handouts of apple slices and pieces of hot dog as rewards. “First they were sitting around and relaxing on the treadmill. When [the machine] started, they were puzzled and could not understand why they were moving away from their food,” says co-author Charles Robbins, a biologist at the center. Instead of walking, the bears tried crawling to reach the food. Eventually, the researchers increased the treadmill speed so the bears had to walk.

“The bears did an excellent job,” says Anthony Carnahan, lead author of the study. “Some of them learned a lot quicker than others.”

Each bear walked about 6 minutes on the treadmill at varying slopes (see video, above). The researchers measured the amount of oxygen the bears used while walking and could estimate the calories they consumed. The most energy-efficient walking speed across all slopes for the bears was about 4.2 kilometers per hour, they report today in the Journal of Experimental Biology.

Next, the researchers compared that pace with tracking data from 30 grizzly bears wearing GPS collars near Yellowstone National Park. The GPS data revealed the bears usually walk at only 2 kilometers per hour, comparable to a slowly hiking human. “It turns out that they don’t move as efficiently as they could,” Carnahan says. Although their speed isn’t the most energy efficient, it gives them time to look for food while they wander. The wild bears also preferred paths that were either flat or had shallow slopes—no more than a 10% grade uphill or downhill.

Unfortunately, that means many hikers will continue to encounter grizzlies—an experience that can invoke awe, fright, and curiosity for both bears and humans, Robbins says. He hopes the findings can help people understand why they might encounter bears and do what it takes to stay safe. 

The research also adds a vital piece to the puzzle of energy dynamics in the bear world, Nielsen says. He’s putting together an “energy map” for grizzly bears based on food availability in various habitats and is excited about integrating the findings into his work. Biologists might be able to better understand how much and how fast bear populations can recover from recent drops in population if they know their energy needs and how many calories are available in the wild, he says. After all, life as a grizzly bear is no picnic.