Michael Bisons, also known as "buffalos," number about 5,000 in the park. They are quite peace-loving if you don't get too close to them. However, if you breach the recommended safety distance of 60 feet, they quickly turn into aggressive furies that have been known to gore tourists and cause serious injuries. On a hiking trail, we didn't even notice a bison lying in the sand behind a stand of trees until it suddenly stood up when we got too close. We cautiously stepped back, and since there was no way to continue on our path without upsetting the buffalo, we reluctantly turned around.
Even on the park roads, you sometimes encounter these buffalo, which leisurely trot from one grazing spot to another and are not afraid of anything or anyone. It's quite exciting when you're sitting in a rental car and one of these buffalo approaches!