Check out more of Steve Hinch's work at Travels in Bear Country
Undoubtedly, one of the most majestic animals at Yellowstone is the American Bison. Every winter they travel some 200 miles west to avoid the park's deepest snow. Their migration takes them along the Firehole River, into Madison Valley and various other geothermal areas where the snow is shallow making it easier to search for food. Unfortunately, this migratory pattern lead bison outside of Yellowstone where they are no longer protected. This creates a conflict with local ranchers due to the small risk of transmitting brucellosis disease to their cattle. (Note: Yellowstone's bison are the sole truly free-ranging population.
In the early 1800's, an estimated 65 million bison roamed throughout the continent of North America. Presently, the herd is about 3,500 strong. In 1987, Drs. Frank and Deborah Popper, introduced the Buffalo Commons proposal. This initiative suggests we restore the drier parts of the Great Plains (argued to be unsustainable) to native prairie, by reintroducing the American Bison, which once grazed the shortgrass prairie. The Poppers envisioned an area of native grassland roughly 10-20 millian acres in size, affecting ten Western U.S. states.
Here are some more groups fighting for the American Bison: