A century ago, wolves were not charismatic attractions for visitors to the park. They were perceived as a threat to the park and over time slowly removed from the protected from human-caused mortalities. Since their introduction to Yellowstone the park has experienced significant changes. The grazing habits of the deer and elk changed and as a result, the course of the rivers changed, as well. In 1973, the US Fish and Wildlife Service listed the northern Rocky Mountain wolf as an endangered species annually, from every corner of the globe and designated Greater Yellowstone as one of three recovery areas.