Humans are a much bigger problem than wolves for a caribou herd in the oil sands area of Alberta, Canada, scientists reported last week in Frontiers in Ecology.

Studies of scat of moose, caribou and wolves in the area showed that caribou accounted for only 10 percent of the animals consumed by wolves. Eighty percent of the wolves’ diet was deer, with moose making up the remainder. Wolves’ preference for deer, the researchers conclude, draws them away from the areas where caribou thrive.

But the oil sands contain the second largest reserve of petroleum in the world, and so they face a heavy human presence as they are developed. And by looking at hormone levels in caribou scat, the scientists found that when humans were most active in an area, caribou nutrition was poorest and psychological stress highest. When oil crews left, the animals relaxed and nutrition improved.

The scientists reported that removing wolves, favored by government and industry, could do serious damage to the ecosystem, and fails to help preserve the caribou. (The study was paid for by Statoil Canada, an energy company with oil leases in the area.)