Everybody else leaves the park for private property that surrounds the park, including the wolves. Upon return of the spring, the elk naturally gravitate back into Yellowstone. The bison need some encouragement. One way to encourage their return is to herd them back using helicopters. This is the cause of concern from certain environmental groups.
Significant conflicts exist with nearby ranchers.
Forty acres of grassland are required to support each Black Angus that is the predominant steer raised in beef production. Bison also carry brucellosis which when transmitted to cattle is terminal. Cattle ranching is not that prosperous a business to begin with, add the competition for grass and a disease and it is understandable why the ranchers are pleased when the bison are herded back to the confines of the park. By the way, you know the classic painting of Indians killing bison with bows and arrows, rarely if ever happened. Indians had two methods of harvesting bison, one was to drive them off a cliff and the other was to dig a pit and drive them into the pit.