"The American Bison's recovery from near extinction parallels what happened to the European Bison, Bison bonasus. Once abundant and widespread in northern latitudes, their decline in several countries since the 6th century has been documented. The last wild populations in Poland and the Caucasus Mountains became extinct early in the 20th century. They now exist as managed, reintroduced populations in Poland, Russia, and the Caucasus. In North America, the wild population once numbered in the tens of millions. The herds were gradually being reduced by hunting pressures before the Civil War, and after the war, with westward expansion, American Bison were pushed almost to extinction. In the 1880s, when only 541 animals were counted, conservation efforts began in earnest. Now there are more than 150,000 animals, 90 percent of which live on private lands. Bison graze on prairie grasses, roaming in herds of thousands of individuals. They, Brown Bears, and Moose are the largest land mammals in North America."

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account