Later even the bones were collected for fertilizer. By 1889, only about 550 bison could be found alive in the United States. A few were protected by early conservationists and together with others bred in zoos and on ranches, they were reintroduced into parks and refuges. Their weight is concentrated in their forequarters. There are two subspecies of bison, plains bison and wood bison.
Females are about one foot shorter.
Male bison of both subspecies weigh 900 to 2,000 pounds. The female, smaller than the male, averages a height of five feet at the shoulder and weighs about half as much as the bull, rarely exceeding 900 pounds. A bison's appearance is led by its massive head that is crowned by a dark brown curly 'hairpiece' between two upwardly curving horns. The bison's foreparts are covered with this dark, woolly mane and beard, that is longer on the plains than the wood subspecies. The horns of a wood bison are longer and straighter than the plains bison.