American Bison: Profile and Information

The American bison (Bison bison), also known as the American buffalo, or simply bison or buffalo, is an American bison species that once occurred in North America.

By 9000 BCE, its historical range was known as the Great Bison Belt, a tract of rich grasslands from the Gulf of Mexico to Alaska, South Georgia, and the Atlantic Seaboard (as far north as New York).

It was close to extinction by a combination of slaughter & commercial hunting in the 19th century and the bovine disease from cattle.

Two ecotypes or subspecies have been recognized; the plains bison (B. b. bison), which is smaller in size and has a more rounded hump. The other subspecies is the wood bison (B. b. Athabasca); it is the larger among the two with a taller square hump.

The wood bison is regarded as one of the world’s largest species of still-living bovid. Compared to the extant land animals in North America, the bison is the longest and heaviest but comes second after the moose in tallness (height).

The American bison is the national mammal of the United States of America.

Scientific Classification

Characteristics

Bison have two coats depending on the season: a lightweight, lighter-brown summer coat and a long, shaggy, dark-brown winter coat.

Females are significantly smaller and less heavy than males. Wood bison are occasionally seen in larger sizes and plain bison in smaller ones.

Head-rump lengths at maximum may be up to 11 ft 6 in (3.5 m) for males and 9 ft 4 in (2.85 m) for females, and the tail adding 1 ft 0 in – 3 ft 1 in (30 – 95 cm).

Heights at withers in the species can range from 5 ft 0 in – 6 ft 1 in (152 – 186 cm) for B. b. bison while B. b. Athabasca reaches over 6 ft 7 in (2 m). Typically, weights can range from 701 – 2,599 lb (318 – 1,179 kg), 1,014 – 2,178 lb (460 – 988 kg) with medians of 1,607 – 1,747 lb (730 – 792.5 kg) (B. b. bison) and 2,080 lb (943.6 kg) (B. b. Athabasca) in males, and 790 – 1,410 lb (360 – 640 kg) with medians of 992 – 1,097 lb (450 – 497.6 kg) in females.

The lowest weights representing a typical weight are probably around the age of sexual maturity at 2 – 3 years of age.

The heaviest B. b. bison weighed 2,800 lb (1,270 kg), while some specimens were rumored to have weighed 3,000 lb (1,360 kg). B. b. Athabasca is significantly heavier and larger than B. b. bison, and when raised in captivity, bison are known to grow abnormally large and weigh up to 3,801 lb (1,724 kg).

The forequarters and heads of both sexes are massive, and they both have short, curved horns that can grow up to 2 ft (60 cm) long with 3 ft (90 cm) to 4 ft (124 cm) width, which they use for defense and in fighting for status within the herd.

The American bison are herbivores grazing on the sedges and grasses of the North American prairies. Their daily routine involves two-hour periods of resting, grazing, and cud-chewing, then migrating to a new area to graze.

Sexually mature males may try to start mating with females by the age of 2 – 3 years, although, in the presence of mature bulls, they may not be able to compete with females until they reach the age of 5.

Calves are lighter in color for the first 2 months of life than mature bison.

Reproduction and Social Behavior

The female bison (cow) lives in maternal herds, including other females and their young. Male juveniles leave their maternal herd at around 3 years old and join other males in bachelor herds or live alone.

The male and female herds do not mingle until the mating season, which can occur from July to September. Female herds may include a few older males.

During mating season, dominant males maintain a small group of females for mating. Individual males (bulls) “tend” females until they can mate by following them and chasing away other males.

The tending male shields the female’s vision with his body so she won’t see the other rival males.

A rival male may roar or bellow to get the female’s attention, and the tending male has to roar or bellow back. The most dominant males mate in the season’s first 2 to 3 weeks. Males show no form of paternal care.

Both male and female bison herds have dominance hierarchies. A bison’s dominance is said to be related to its birth date. American bison born earlier in the mating season are more likely to be more dominant and larger than adults.

Bison are known to pass their dominance to their offspring. The younger bison of a generation tend to have a lesser fertility rate than the older ones.

Bison mate in August – September, with the gestation period lasting up to 285 days. Females nurse their young (calf) for at least seven or eight months. The female bison becomes mature enough to produce a calf at the age of 3 years.

Compared to other northern ungulates, such as caribou and moose, the birthing period for an American bison in boreal biomes is protracted. The American bison have been seen to display homosexual behaviors.

The lifespan of an American bison in the wild is 15 years, and may live up to 25 years in captivity.

Behavior and Ecology

Bison are known to migrate in herds. The migration of herds occurs in two ways: directional and altitudinal.

The summer ranges of the American bison appear to be influenced by the size and interspersion of foraging sites, seasonal vegetation changes, the number of biting insects, and the rut.

Water availability and the preserve’s size may also be a factor. American bison are herbivorous animals. They mainly graze on sedges and grasses.  

Habitat

American bison live on prairies & plains and in river valleys. Typical habitat is semi-open or open grasslands, semiarid lands, sagebrush, and scrublands.

American bison also graze mountainous or hilly areas with steep slopes. They are not regarded as high-altitude animals.

However, American bison in the Yellowstone Park bison herd are often found at elevations above 8,000 ft (2,400 m) and in mountain valleys of Henry Mountain to an altitude of 10,000 ft (3,000 m).

The first thoroughfare of North America, except the routes of the mound builders and the time-obliterated paths of muskox and mastodon, were the traces made by deer and bison between feeding grounds & salt licks and in seasonal migration.