The largest of our hoofed mammals, bull bison are 10 feet long (not counting the 20 inch tail), and weigh nearly a ton; cows are more than six feet long and weigh up to 1,000 pounds. They are dark brown, have a massive hump over the shoulders, a shaggy head, and horns on both sexes.
Once wolves and grizzly bears preyed on young and old bison, but large size and herding habits protect bison from most non-human predators. No match for the firearms of the market hunters, bison no longer occur in Colorado in the wild – the last of them were killed in South Park in 1897. Today, captive herds in Colorado are officially called "livestock," not wildlife.
Range: Once bison lived nearly statewide in Colorado, most abundant on the plains, in the mountain parks and western basins. They also lived in forests and above timberline. Bison were migratory, moving in huge herds in a vast circuit across the plains, responding to the opportunity of new grass just beyond the horizon.
Reproduction: Bison breed in late summer. Dominant bulls mate with several cows. A single calf is born after a gestation period of about 9 1/2 months. Cows are mature and breed at three years old; bulls seldom have sufficient status to breed until they are seven or eight. Longevity is 20-30 years.
By David M. Armstrong
Department of Ecology & Evolutionary Biology
Environmental Studies Program, University Museum of Natural History
University of Colorado-Bouldermausmann@aol.com