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American Bison Bison bison


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American Bison
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Family: Bovidae, Cattle, Goats, and Sheep view all from this family

Description North America’s largest land mammal. Has a distinctive humped profile with larger forequarters and smaller hindquarters; these traits are more pronounced in males. The brown wooly pelage is thickest around the neck, extending onto the shoulders and back in males. Males also have larger horns, which are stouter and more curled; female horns are more slender with upward pointing tips. Calves are reddish. Hair is longer in the winter. The Endangered Wood Bison (B. b. athabascae) from western Canada is slightly taller, darker, and woolier, with a larger hump than the Plains Bison (B. b. bison).

Dimensions 3.0-3.8m, 43-90cm, 460-907kg; / 2.1-3.2m, 43-90cm, 360-544kg

Breeding Breeding season is July-August, gestation length is 285 days, and females have only a single calf with birth coinciding with spring greenup. Females leave the herd and lie down to give birth. The female fiercely defends the newborn calf. Sexual maturity is reached at age 2.

Habitat Forests & woodlands, Grasslands & prairies, Meadows & fields

Range Rocky Mountains, Western Canada, Alaska

Discussion Wallows 2-3m wide are used by all ages and sexes. Prairie rock rubs worn smooth by 10,000 years of use usually rest at the bottom of a slight depression formed by countless hoofs circling the stone as the bison rubbed against it. Tens of millions of bison were nearly hunted to extinction (probably fewer than 1000 animals left) at the end of the nineteenth century, the species had recovered to ca. 150,000 animals by 1995, with 90% privately owned. Typically grazes in herds of 4-20, these groups sometimes merge into much larger congregations. Herds provide protection from predators, and stampedes are a predator-avoidance behavior. Males have a repertoire of threat displays, both visual and vocal, to establish dominance relationships, but rarely resort to all-out battles. When they do occur, these battles are epic, the large bulls slamming into each other, shearing out gouts of hair with their horns, and on rare occasions, dying from a horn that penetrates the ribcage. Most breeding happens in a 2-week period, and the one-third of the males that are dominant breed with two-thirds of the females. This means that the large male bison are heavily selected for fighting specialists, while the much smaller female’s reproductive success depends more on competition for food. When a cow comes into estrus, she is quickly tended by a bull, who may then be replaced by a more dominant bull. Reaching their highest density in mixed and short-grass prairies, these gregarious grazers can survive in a variety of open habitats.