Grizzly on a treadmill/Washington State University

Surprise, surprise – scientists at Washington State University (WSU) have decided grizzly bears like trails for the same reason humans do.

Trails make cross-country travel a whole lot easier.

Alaskans who have spent a lot of time deep in the wilderness, where the only trails are animal trails, will not be surprised by this. Humans naturally gravitate toward bear trails, caribou trails, moose trails and sheep trails because any trail makes walking easier than bashing through the brush.

Bears turn to human trails for the very same reason.

This would seem so obvious it need not be studied, but now the obvious has been documented by researchers from WSU’s Bear Research, Education and Conservation Center who put grizzlies on treadmills to study their energy use and then examined 11 years of global positioning system (GPS) data from radio-collared grizzlies roaming Yellowstone National Park.

What the treadmill told them, according to a research summary in the Journal of Experimental Biology, is that the bears burn a lot of calories going uphill and down.

“We trained captive grizzly bears to walk on a horizontal treadmill and up and down 10 percent and 20 percent slopes,” the study said. “The cost of moving upslope increased linearly with speed and slope angle, and this was more costly than moving horizontally. The cost of downslope travel at slower speeds was greater than the cost of traveling horizontally but appeared to decrease at higher speeds.”

The anti-diet

When lead researcher Anthony Carnahan and his colleagues turned to the GPS data, they found that bears seemed to recognize these energy costs.

The animals spent twice as much time traveling on nearly flat surfaces as on slopes and when traveling uphill or downhill, they chose paths “approximately 54 percent less steep and (calorie) costly than the maximum available slope,” the researchers reported.

For animals that spend the snowless season trying to get as fat as possible to survive a winter-long hibernation, every calorie counts. And fat accumulation, whether for humans or bears, is at the end of the day a rather simple matter of consuming more calories than the body burns.

In the interest of calorie conservation, bears even appear to favor trails built to National Park Service standards aimed at making life easy for hikers.

“For example, National Park Service (1998) construction guidelines for trails recommend that gradients not exceed 10 percent in steep terrain,” the study says. “With two-thirds of the movement paths of Greater Yellowstone Ecosystem grizzly bears occurring within this gradient range (i.e. zero to 10 percent), it should not be surprising that they choose movement paths similar to humans and commonly use trails built for humans.”

Park Service trail builders can probably claim some credit for making life a tiny bit easier for the bears of Yellowstone with the more 900 miles of trail built in the park since 1872, but the same trails have come with consequences.

Of the eight people killed by bears in the park, five were either hiking on trails or in trail-laced campgrounds, according to the Park Service, and the three most recent deaths – two in 2011 and one in 2015 – all involved hikers on trails.

Carnahan and his team warned that the dangers of the shared use of trails by people and bears could “be exacerbated by the increasing popularity of trails for other forms of recreation, such as mountain biking when bears and humans encounter each other at high speed with little warning.”

Realistic risks

The threat of being attacked by a bear scares the bejesus out of many, but the Yellowstone experience well illustrates how rare such attacks.

Compared to the eight people killed by bears in the park since 1872, the agency notes 121 people drowned, 21 died from burns after falling into the hot springs, 26 fell victim to suicide, seven were killed by falling trees, six perished in avalanches, and five succumbed to lightning strikes.

The park in 2019 estimated the odds of being killed by a bear at 1 in 2.7 million visits, although that worsened to 1 in 232,613 person travel days in the park’s backcountry.

Bear attacks and deaths are the most common in the backcountry in Alaska. Both of those killed by bears last year in the state were miles from the nearest road.

Alaskan Daniel Schilling was building a trail in the Kenai Mountains near the historic mining community of Sunrise when he was attacked and killed in July. A 22-year-old Ohio hunter died in September after being attacked by a bear while packing moose meat from a kill site to a remote camp in the Alaska Range.

The WSU study did add some interesting information on bear running speeds. The researchers reported that “high-speed predatory chases of either calves or adult elk averaged 8.9 m s⁻¹ (about 20 mph) and were much shorter in duration (12 seconds, plus or minus five) and distance (107 meters, plus or minus 35), presumably because the bears were well above their estimated aerobic capacity.”

In longer chases, some of which covered nearly three miles, speeds fell to under 4 mph.

The latter observation underlines the old Alaska advice that the best way to avoid bear problems is to avoid bears. If you see them before they see you and increase your distance from them, it’s an energy-losing proposition for them to come chasing after you.

The other big takeaway from the study is that place where people should be most alert is where they are usually least alert – on trails. Given the similar gradients on human and animal trails, this would appear to apply to all 49th state trails whether manmade or not.

This should be obvious to anyone on Kodiak Island or the Alaska Peninsula – where bear trails are often large and obvious – but might not be so obvious in areas where moose and caribou trails provide the most obvious routes of travel.

And, of course, this time of year with bears soon to emerge from hibernation, there are ski, snowshoe and snowmachine trails that are just as attractive to bears as any other trail. Anyone who spent much time on these trails in Alaska in April is certain to have run into the tracks of bears on them, especially in mountainous areas where grizzlies tend to den.

The good news is that with the snow burying alder and mountain thickets in the high country bears are a lot easier to spot and avoid than in summer.

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