In the spring, this coat is shed and replaced by one that is short and light-brown. Hair on the head, neck, shoulders, and forelegs remains long and shaggy throughout the year. A beard also hangs from the chin of the animal’s huge, low-slung head.
An average American bison has a head and body length of 7 to 12.5 feet (2.1 to 3.8 meters) and a shoulder height of 5 to 6.5 feet (1.5 to 2 meters). It weighs between 700 and 2,200 pounds (320 and 1,000 kilograms). The animal’s relatively short tail is 12 to 35 inches (31 to 89 centimeters) long and ends in a tuft of hair.
The American bison species is divided biologically into two subspecies: the plains bison (Bison bison bison) and the wood bison (Bison bison athabascae). The main physical difference between the two is the color of the hair on the shoulders. On the plains bison, this hair is lighter in color than the hair on the rest of its body. The difference in hair color on the wood bison is not so pronounced.
The bison is a fast runner and good swimmer, and has a keen sense of smell. It is active during both day and night, feeding on prairie grasses and sedges (grasslike flowers).
Bison usually travel in herds, although some males (bulls) tend to be solitary. Mating season lasts from June to September. The gestation (pregnancy) period of the female American bison is about 285 days. The calves, which are reddish-brown in color when born, may nurse for up to a year.
Habitat and current distribution
In the United States in the early years of the twenty-first century, about 25 herds of plains bison live in parks and wildlife reserves, numbering about 16,000 animals.
Plains bison are found primarily in Yellowstone National Park in north-western Wyoming, southern Montana, and eastern Idaho. This herd numbers about 3,600. Additional plains bison are located in other parks and nature reserves.
There are an estimated 140,000 animals living on private ranches in the western United States. Wood bison exist in a number of sanctuaries in Canada, including Wood Buffalo National Park in northern Alberta and southern Northwest Territories. The number of Canadian wood buffalo is believed to be more than 5,000.
History and conservation measures
These large animals were an essential part of the culture of many Native American people, who depended on the American bison for food and clothing. As American and European settlers moved west during that century, the number of bison began to decline. The animals were hunted for their hides, meat, and tongues, which were considered a delicacy.
They were shot from trains for sport. And as part of the American government’s strategy to subdue Native Americans, bison were slaughtered by the millions. By the late nineteenth century, only a few hundred of each subspecies remained in the wild.
In 1902, the American government placed a herd of some 40 captive and wild plains bison under protection in Yellow-stone National Park. This herd grew into the one that exists in the park today.
In 1922, the Canadian government established Wood Buffalo National Park to protect the last surviving wood bison. Unfortunately, plains bison were shortly afterward released into the park, where they mated with the wood bison.
The resulting offspring were a hybrid, or genetic mixture, of the two subspecies. In the late 1950s, a small herd of genetically similar wood bison were located in the park. Although scientists allowed these animals to breed only with each other, no one is certain whether any genetically pure wood bison currently exist.
Beginning in 1990, Montana Department of Livestock workers shot plains bison that wandered outside of the boundaries of Yellowstone National Park. Even though the animals are protected within the park, a state-federal agreement gives Montana officials the right to kill bison if they cross onto private land.
Both Montana officials and private ranchers feared the bison would infect cattle grazing near the park with brucellosis, a disease that causes cows to abort their calves. Conservationists (people who protect the natural world) claimed that there were no cases of the disease being transmitted from a bison to a cow.
Despite the lack of scientific evidence, Montana officials remained fearful. During the harsh winter of 1996–97, more than 1,000 bison that roamed outside of the park in search of food were slaughtered.
In the early 2000s, legislation was written in Montana allowing “sport hunting” of the bison that left the park and crossed into Montana. This would mean that private citizens with a permit could shoot bison for sport.
The situation was becoming urgent because Yellowstone, with a population of 3,600 bison, had become overcrowded with bison and herds had been traveling out of the park to graze. Conservationists call for better means of controlling the population in the park and more research into the transmission of the brucellosis disease.