Yellowstone Park Grazer is a term used to describe two of the most iconic animals that inhabit Yellowstone National Park: ELK and BISON. ELK, also known as wapiti, are large deer-like mammals with antlers that can reach up to five feet in length. BISON, also known as buffalo, are large, shaggy-haired mammals that can weigh up to 2, 000 pounds. Both ELK and BISON are herbivores, meaning they graze on grasses, shrubs, and other vegetation found in the park.