Wood bison are the larger of the two subspecies of modern American bison. Adult males are approximately 6 feet tall at the shoulder, 10 feet long, and weigh more than 2,000 pounds. The females are smaller, generally weighing around 1,200 pounds.
The American bison occurs in two subspecies in North America, the plains bison (Bison bison bison) and the wood bison (Bison bison athabascae). Plains bison are somewhat smaller than wood bison. A bison’s head and forequarters are massive and seem out of proportion to the smaller hindquarters. A bison’s backbone begins to rise just ahead of the hips and reaches its maximum height about or behind the front shoulder. From above the shoulder, the hump drops almost straight down to the neck. In wood bison, the hump is taller and the highest point of the hump is further forward than in plains bison.
Bison have horns that curve upward. The horns of a bull are larger and heavier than the horns of a cow. In late fall, a bison’s coat is a rich, dark brown. As winter progresses, the coat changes color and is lighter colored by spring. When the weather warms, the hair loosens and hangs in patches until it is completely shed and replaced with new hair in the late spring. The hair on the chin resembles a goatee and is more pointed in wood bison. Older animals tend to have more hair on their heads.