Wolves are fierce predators, but hunting is still dangerous. Elk and bison, their usual prey in Yellowstone National Park, have sharp hooves that can injure or even kill. Hunting in groups helps wolves subdue their prey more easily—but a group that’s too big puts more wolves in danger. So they form teams of different numbers depending on the prey they’re after.
Wolves can hunt elk alone or in small groups, says Daniel MacNulty, a wildlife ecologist at Utah State University. But a 1,000-pound bison is a much more formidable foe. “A single wolf has virtually no chance of taking down a bison by itself,” says MacNulty. He’s found that wolves seem to know this, and are more likely to attack when they have a group of the right size.