File:American Bison, Madison River Area, Yellowstone National Park (2484648796).jpg

We came across this Bison shortly after entering the west side of Yellowstone National Park along the Madison River.

The American bison (Bison bison) is a North American species of bison, also commonly known as the American buffalo. Some consider the term "buffalo" somewhat of a misnomer for this animal, as it is only distantly related to either of the two "true buffalo," the Asian water buffalo and the African buffalo. However, "bison" is a Greek word meaning ox-like animal, while "buffalo" originated with the French fur trappers who called these massive beasts bœufs, meaning ox or bullock – so both names, "bison" and "buffalo," have a similar meaning. In reference to this animal, the term "buffalo," which dates to 1635, has a much longer history than the term "bison," which was first recorded in 1774. The American bison is more closely related to the wisent or European bison.

These bison once roamed the grasslands of North America in massive herds; their range roughly formed a triangle between the Great Bear Lake in Canada's far northwest, south to the Mexican states of Durango and Nuevo León, and east along the western boundary of the Appalachian Mountains. Two subspecies or ecotypes have been described: the plains bison (Bison bison bison), smaller in size and with a more rounded hump, and the wood bison (Bison bison athabascae) – the larger of the two and having a taller, square hump. Furthermore, it has been suggested that the plains bison consists of a northern (Bison bison montanae) and a southern subspecies, bringing the total to three. However, this is generally not supported. The wood bison is one of the largest species of bovid in the world, surpassed by only the Asian gaur and wild Asian water buffalo. It is the largest extant land animal in North America.

The only continuously wild bison herd in the United States resides within Yellowstone National Park. Numbering between 3,000 and 3,500, this herd is descended from a remnant population of 23 individual mountain bison that survived the mass slaughter of the 1800s by hiding out in the Pelican Valley of Yellowstone Park. In 1902, a captive herd of 21 plains bison was introduced to the Lamar Valley and managed as livestock until the 1960s, when a policy of natural regulation was adopted by the park.

The end of the ranching era and the onset of the natural regulation era set into motion a chain of events that have led to the bison of Yellowstone Park migrating to lower elevations outside the park in search of winter forage. The presence of wild bison in Montana is perceived as a threat to many cattle ranchers, who fear that the small percentage of bison that carry brucellosis will infect livestock and cause cows to abort their first calves. However, there has never been a documented case of brucellosis being transmitted to cattle from wild bison. The management controversy that began in the early 1980s continues to this day, with advocacy groups arguing that the Yellowstone herd should be protected as a distinct population segment under the Endangered Species Act.