Two bison are silhouetted against the backdrop a colorful thunderstorm. Yellowstone was home to the last, wild, free-roaming bison at the turn of the 19th century. In less than one hundred years, wholesale slaughter reduced the number of bison from an estimated high of sixty million to under three thousand animals. These remaining bison found refuge in Yellowstone National Park. Now thousands of these animals roam the Yellowstone ecosystem.