Energy Cost
According to Vollrath, walking uphill for elephants, which weigh 4.4 to 5.5 tons (4 to 5 metric tons), is like a human pushing a car uphill.
"That's a lot harder than pushing on level ground. … You put a lot of sweat into pushing up a hill, if you can even do it," he said.
In the current study, Vollrath and his colleagues calculate that a walk up a 328-foot (100-meter) hill requires an elephant to burn the energy it gains in a half hour of foraging.
"You have to spend a lot of time eating just to walk up a hill," Vollrath said.
Otherwise the elephants pay for the uphill hike with their body reserves. And unlike a car, he adds, elephants can't coast downhill.
"Walking downhill, if you are a hiker, is as much sweat as walking up hill," he said.
So when confronted with a hill, elephants prefer to take a detour along level terrain, the researchers conclude.
Tracking Elephants
The team's finding is based on tracking data collected from more than 50 elephants.
The elephants were fitted with collars that communicated their position to a satellite or cell phone every hour.
When the tracking data was plotted on a topographic map, the researchers noticed the elephants preferred to stick to level land, even when a hilltop promised abundant food.
"We have to look into this—the energy cost of terrain—and see how to integrate it into our conservation decisions," Vollrath said.
Stanford University's O'Connell-Rodwell says farmers in India are already taking elephants' aversion to hills into their planning.
"[They] have used the concept of ditches to prevent crop-raiding elephants, because elephants do not like steep inclines, in particular a steep decent and then steep rise," she said.
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