In the run up to hibernation, grizzly bears go on a colossal binge, consuming as many calories as possible to get them through the long winter. Yet, little was known about how much energy the massive mammals use as they shamble around their rugged territories. “Moving across the landscape in search of food can be a huge energetic expense for some animals,” says Anthony Carnahan, a graduate student in the School of Biological Sciences.
Fortunately, the Washington State University Bear Research, Education and Conservation Center (WSU BREC), where Carnahan is based, is home to 11 bears, including four that formerly lived in Yellowstone National Park, so he and Charles Robbins (also at WSU BREC) decided to measure the animals’ metabolic rates as they sauntered on the flat, and up and down gradients to find out how much energy they use on a daily basis. The team publishes their discovery that grizzly bears prefer to walk on shallow paths to save energy in Journal of Experimental Biology, explaining why the animals often appear on human hiking trails.
After months of patiently measuring the bears’ oxygen consumption at speeds ranging from 0.4 to 1.3m/s on the level and gradients up to 20deg to calculate how much energy they used, it was clear that ascending and descending the slopes was quite costly, although the bears used less energy bowling downhill at higher speeds. Most surprisingly, the bears didn’t seem to have much spare gas in the tank to maintain long high-speed pursuits. They consume similar amounts of energy to climbing humans, wolves and wild cats, in contrast to fleeing elk and deer, which use 46% less energy than grizzlies over mountainous terrain.
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