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If you’ve ever worried about a bear after your picnic basket, you might want to take the more difficult, hilly trail to your destination. That’s the take-home message from a new study, in which researchers rolled nine bears on treadmills – a first for science – and found that they, like their lazier human counterparts, prefer them. flat paths to save energy. Scientists say the study could help explain why bears are often found around popular hiking trails.
Grizzly bears (Ursus) need to recharge their batteries before going into winter hibernation. As opportunistic omnivores, they eat just about anything – berries, roots, grass, insects, and meat – to gain weight. It requires a lot of foraging, but it was a mystery which paths they chose to search for food. “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 who was not involved in the study.
To find out how grizzly bears use up their energy foraging for food, researchers at Washington State University’s Bear Research, Education, and Conservation Center placed a treadmill in a custom 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 on different slopes, both uphill and downhill.
Training bears was no easy task. Before starting their experiments, the researchers acclimatized the bears to the treadmill enclosure for 2 months, using generous distributions of apple slices and hot dog pieces as rewards. “First they would sit and relax on the treadmill. When [the machine] started, they were puzzled and couldn’t understand why they were straying from their food, ”says co-author Charles Robbins, biologist at the center. Instead of walking, the bears tried to crawl to reach the food. Eventually, the researchers increased the speed of the treadmill, so the bears had to walk.
“The bears did a great job,” says Anthony Carnahan, lead author of the study. “Some of them learned much faster than others.”
Each bear walked about 6 minutes on the treadmill at varying inclines (see video above). The researchers measured the amount of oxygen the bears used while walking and were able to estimate the calories they were consuming. The most energy-efficient walking speed on all slopes for the bears was around 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. GPS data revealed that bears typically walk only 2 kilometers per hour, which is comparable to a human walking slowly. “It turns out they don’t move as efficiently as they could,” Carnahan says. Although their speed isn’t the most energy efficient, it does give them time to forage for food while they roam. Wild bears also preferred flat or shallow trails – no more than 10% uphill or downhill.
Unfortunately, this means that many hikers will continue to encounter grizzly bears – an experience that can arouse awe, fear and curiosity for both bears and humans, Robbins says. He hopes the findings will help people understand why they might encounter bears and do whatever it takes to stay safe.
The research also adds a vital piece to the energy dynamics puzzle in the bear world, Nielsen says. He is preparing an “energy map” for grizzly bears based on food availability in various habitats and is excited to incorporate the results into his work. Biologists may be able to better understand how much and how quickly bear populations can recover from recent population declines if they know their energy needs and the number of calories available in nature, he says. After all, grizzly bear life isn’t a picnic.
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