The bison is the largest mammal in North America and this bull here is a particularly beautiful example. He stands confidently on the lush meadow with strong legs, grazing with slow relish. Suddenly his head jerks up. Was it something he heard? The bison turns his large head to the side and looks out over the wide plain. Nothing there. He continues to graze on. This big guy is quite peaceful. But if he has to, he defends himself and his herd courageously. What you would least expect: He can even run really fast. Bison can reach speeds of up to 35 miles per hour! Once they pick up speed, they hurtle towards their opponents like an avalanche of hooves. Fortunately, that only happens in an emergency.