WHAT IS A BISON?
The American bison (Bison bison), also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds. Their range once roughly comprised a triangle between the Great Bear Lake in Canada's far northwest, south to the Mexican states of Durango and Nuevo León, and east along the western boundary of the Appalachian Mountains. Because of commercial hunting and slaughter in the 19th century, the bison nearly went extinct and is today restricted to a few national parks and other reserves.
Two subspecies or ecotypes have been described: the plains bison (Bison bison bison), smaller in size and with a more rounded hump, and the wood bison (Bison bison athabascae) – the larger of the two and having a taller, square hump. The wood bison is one of the largest species of bovid in the world, surpassed by only the Italian Chianina, the Asian gaur and wild Asian water buffalo. It is the largest extant land animal in North America.
A bison has a shaggy, long, dark brown winter coat, and a lighter weight, lighter brown summer coat. As is typical in ungulates, the male bison are slightly larger than the female. Plains bison are often in the smaller range of sizes, and Wood bison in the larger range. Head-and-body length ranges from 2 to 3.5 m (6.6 to 11.5 ft) long, the tail adding 30 to 91 cm (12 to 36 in). Shoulder height in the species can range from 152 to 186 cm (60 to 73 in). Typical weigh can range from 318 to 1,000 kg (700 to 2,200 lb). The heaviest wild bull ever recorded weighed 1,270 kg (2,800 lb). The heads and forequarters are massive, and both sexes have short, curved horns that can grow up to 2 feet (61 cm) long, which they use in fighting for status within the herd and for defense.
Bison are herbivores, grazing on the grasses and sedges of the North American prairies. Their daily schedule involves two-hour periods of grazing, resting and cud chewing, then moving to a new location to graze again. Bison mate in August and September; gestation is 285 days. A single reddish-brown calf nurses until the next calf is born. If the cow is not pregnant, a calf will nurse for 18 months. Bison cows are mature enough to produce a calf at 3 years of age. Bison bulls may try to mate with cows at 3 years of age, but if more mature bulls are present, they may not be able to compete until they reach 5 years of age. Bison have a life expectancy of approximately 15 years in the wild and up to 25 years in captivity.
For the first two months of life, calves are lighter in color than mature bison. One very rare condition is the white buffalo, in which the calf turns entirely white. White bison are considered sacred by many Native Americans.
Some consider the term "buffalo" somewhat of a misnomer for this animal, as it is only distantly related to either of the two "true buffalo," the Asian water buffalo and the African buffalo. However, "bison" is a Greek word meaning ox-like animal, while "buffalo" originated with the French fur trappers who called these massive beasts bœufs, meaning ox or bullock – so both names, "bison" and "buffalo," have a similar meaning.
Range and population
Despite being the closest relatives of domestic cattle native to North America, bison were never domesticated by native Americans. Later attempts of domestication by Europeans prior to the 20th century met with limited success. Bison were described as having "wild and ungovernable temper"; they can jump 6 feet vertically, and run 35-40 mph (56-64 kph) when agitated. In combination with their weight, that makes bison herds difficult to confine, because they can jump over or crash through almost any fence.
There are approximately 500,000 bison in captive commercial populations (mostly plains bison) on about 4,000 privately owned ranches.  Under the IUCN Red List Guidelines, commercial herds are not eligible for consideration in determining a Red List designation, therefore the total population of bison calculated in conservation herds is approximately 30,000 individuals and the mature population consists of approximately 20,000 individuals. Of the total number presented, only 15,000 total individuals are considered wild bison in the natural range within North America (free-ranging, not confined primarily by fencing).
Female bison live in maternal herds which include other females and their offspring. Male offspring leave their maternal herd when around three years old and will either live alone or join other males in bachelor herds. Male and female herds usually do not mingle until the breeding season. However female herds may also contain a few older males. During the breeding season, dominant bulls maintain a small harem of females for mating. Individual bulls "tend" cows until allowed to mate, by following them around and chasing away rival males. The tending bull will shield the female's vision with his body so she will not see any other challenging males. A challenging bull may bellow or roar to get a female's attention and the tending bull has to bellow/roar back.
Bison herds have dominance hierarchies that exist for both males and females. A bison's dominance is related to its birth date. Bison born earlier in the breeding season are more likely to be larger and more dominant as adults. Thus bison are able to pass on their dominance to their offspring as dominant bison breed earlier in the season. In addition to dominance, the older bison of a generation also have a higher fertility rate than the younger ones.
Bison are among the most dangerous animals encountered by visitors to the various U.S. and Canadian national parks, and will attack humans if provoked. They appear slow because of their lethargic movements but can easily outrun humans — bison have been observed running as fast as 35–40 miles per hour (56–64 km/h). Bison are more agile than one might expect, given their size and body structure.
Between 1980 and 1999, more than three times as many people in Yellowstone National Park were injured by bison than by bears. During this period, bison charged and injured 79 people, with injuries ranging from goring puncture wounds and broken bones to bruises and abrasions. Bears injured 24 people during the same time frame. Three people died from the injuries inflicted - one person by bison in 1983, and two people by bears in 1984 and 1986.