When a couple of big Wyoming bison decide to mix it up in a Yellowstone campground, get out of the way. The guys are in a mood, and they will chase anything down to fight with it, including cars. Bison rutting season takes place from June through September, with peak activity occurring in July and August. The National Park Service says you must stay at least 25 yards (75 feet) away from bison at all times. They have been known to chase people for long distances, and they are a heck of a lot faster than they look.