Grey wolves have roamed Yellowstone National Park since their reintroduction in 1995, and these apex predators play an essential role in managing the ecosystem. And although bison aren't their usual prey, hunger makes them braver.
While a kick from a large bison can be deadly for a wolf, a calf is easier to lure out from a group, and can keep wolf pups fed for days.
But can the herd save the calf in time?
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Top image: bison calf and grey wolf. Credit: Getty