American bison

Name and taxonomy

English speakers used the word buffalo for the animal as early as 1625. Samuel de Champlain had written of buffles in 1616 after members of the Nipissing First Nation showed him skins and a drawing. The word traces back through Portuguese and Latin to the Greek boubalos. The word bison came into English from French in the 1690s, from a Latin name for the aurochs. In British English, buffalo means only the African and water buffalo.

The species belongs to the cattle tribe Bovini in the family Bovidae. Two forms are recognised: the plains bison, with a rounded hump, and the larger wood bison, with a tall square hump. Some scientists treat them as subspecies and others as ecotypes. Plains languages such as Lakota and Arapaho use separate words for a bison cow and a bison bull. That split probably reflects how central the animal was to daily life.

Evolution and relatives

Nuclear DNA shows the bison's closest living relative is the yak. By that evidence bison sit inside the genus Bos, beside cattle. The European bison is the only other living bison species. Its mitochondrial DNA is closer to cattle and the aurochs, which suggests ancient crossbreeding.

Bison first appeared in Asia about 2.6 million years ago. They crossed Beringia into North America between 195,000 and 135,000 years ago as the steppe bison. New species followed fast, including the long-horned Bison latifrons and Bison antiquus. The modern bison descends from Bison antiquus at the end of the last ice age. American bison can still breed with cattle, and only the female calves of the first cross are fertile.

Appearance

The bison is built front-heavy, with massive shoulders, a deep hump and a broad head. Cows measure 2.13 to 3.18 metres from head to rump, and bulls 3.6 to 3.8 metres. Bulls stand 1.67 to 1.86 metres at the shoulder, and cows 1.52 to 1.57 metres. The tail adds 30 to 95 centimetres. Bulls commonly weigh 460 to 988 kilograms, and cows 360 to 640 kg. Wood bison run larger, and three quarters of the animals over 1,000 kg at Elk Island were wood bison.

The winter coat is long, shaggy and dark brown, and the summer coat is shorter and lighter. The hair is longest on the head, neck and shoulders, and a beard hangs from the chin. Both sexes carry short black horns that curve up and inwards, up to 60 centimetres long. The hooves are black and round. Calves are reddish for their first two months and turn brown by four months. A white bison is very rare.

Habitat and range

Around 9000 BC the range ran from Alaska to the Gulf of Mexico and east almost to the Atlantic. Bison lived in North Carolina as late as 1750. By 1890 wild bison had vanished from almost all of that range. Today wild herds live in parks and reserves across the western United States and Canada, and in northern Mexico. Since 2006 wood bison from Elk Island have also lived in Yakutia in Russia.

The bison is above all a grassland animal. It lives on prairies, plains and river valleys, and in sagebrush and scrub. It also grazes hills and mountains where the slopes are gentle. Yellowstone bison often feed above 2,400 metres, and the Henry Mountains herd reaches 3,000 metres. Bison in Yukon spend the summer on alpine plateaus above the treeline.

Bison trails were the first roads of North America. The herds followed ridge crests and watersheds, and their paths avoided summer mud and winter drifts. Indigenous peoples, explorers and pioneers used the same paths, and some later became railway routes. One heavy trail forded the Ohio at its falls and ran west past Vincennes in Indiana.

Diet and feeding

The bison is a grazer all year round. Grasses and sedges make up nearly all of the diet, and on mixed prairie they supply 79 to 96 percent of it. In hard times it turns to sagebrush and other shrubs. An adult eats about 1.6 percent of its body mass in dry plant matter each day. It needs water every day and eats snow in winter.

A herd grazes for about two hours, then rests and chews the cud, then moves on to fresh ground. It keeps walking while it feeds, so no one patch is grazed bare. In the Hayden Valley of Yellowstone, bison walk about 3 kilometres a day in summer. Herds migrate with the seasons, and some move up and down mountains.

Behaviour and social life

Cows live in maternal herds with their calves, a few young bulls and sometimes an old bull. Bulls leave the maternal herd at about three years and live alone or in bachelor groups of up to 30. The sexes mix only in the rut, from late June to September. Both bulls and cows keep a strict linear rank order. Rank tracks birth date, because calves born early in the season grow larger. An adult cow leads the herd when it travels, and the animals walk in a line.

Bison wallow in shallow pits of dust or mud. Wallowing sheds loose fur, eases insect bites, cools the body and lets bulls spread scent in the rut. The pits hold rainwater and add plant and animal diversity to the prairie. In autumn bison rub their horns on cedars and pines, and the resin seems to keep insects off. Bison swim well and can run at 55 to 70 kilometres an hour. They can also jump nearly 1.8 metres straight up.

Communication and senses

Smell is the bison's sharpest sense, and it is the main way the animal detects danger. Hearing is also good. The eyes pick out a large object at 1 kilometre and a moving one at 2 kilometres. Bison grunt and snort to each other, and a bull bellows or roars during the rut. A tending bull must answer the roar of any challenger.

Scent probably carries most of the messages about breeding condition. Park rangers say the tail shows mood, and a tail held straight up often comes before a charge. Bison ignore wolves that are not hunting, which suggests they read a predator's behaviour closely.

Reproduction and life cycle

The rut runs from late June to September, with the peak in August and September. A dominant bull tends one cow at a time, follows her, and chases off rivals. He blocks her view with his body so she cannot see other bulls. The top bulls mate in the first two to three weeks, and lesser bulls take the cows that remain. Bulls fight, wallow and horn trees more often during the rut.

Gestation lasts about 285 days, so most calves arrive from mid-April to May. A cow leaves the herd to give birth in cover. She has one calf, which weighs 15 to 25 kilograms and can run within hours. Calves nurse for seven to eight months, and most stop before their first birthday. A calf whose mother has no new calf may nurse for 18 months. Bulls take no part in raising the young.

Cows can breed at two to three years, and bulls mature at about three. A bull rarely wins a cow before five or six, when he is big enough to compete. Wild bison live about 15 to 20 years, and some reach 25. In captivity the claimed record is 40 years.

Predators and threats

A healthy adult bull is almost safe from any predator. Wolves take calves, injured cows and weak animals, most often in late winter when snow is deep. A wolf hunt can last from a few minutes to more than nine hours. Calves flee to a cow, to the herd, to a bull, into the middle of a stampede, or into water. When a herd runs, cows with calves lead and bulls guard the rear. Grizzly bears scavenge kills and sometimes take a calf, but a healthy adult may kill the bear instead.

The deepest threat is genetic. All plains bison descend from about 100 founders in six herds, plus 25 wild animals in Yellowstone. Early ranchers crossed some of them with cattle, and cattle DNA now shows up in almost every herd tested. Perhaps only 12,000 to 15,000 bison are free of cattle genes. Bison can also carry brucellosis, which worries cattle ranchers near parks.

Population and conservation

The IUCN lists the American bison as Near Threatened. Estimates in 2010 put the total at 400,000 to 500,000. About 20,500 lived in 62 conservation herds, and the rest in about 6,400 commercial herds. Only about 15,000 count as wild and unfenced, and 31,000 were wild by March 2019. The Yellowstone herd, which began with 25 animals, numbered about 5,900 in 2022.

Herds with little or no cattle ancestry include Yellowstone, the Henry Mountains, Wind Cave and Wood Buffalo National Park. The Nature Conservancy has returned bison to more than a dozen preserves, including one in Indiana in 2016. In 2014 tribes and First Nations signed a bison treaty, the first in nearly 150 years. The Inter Tribal Buffalo Council, formed in 1990, joins 56 tribes with more than 15,000 bison on tribal land. The 2020 Bison Conservation Initiative moves animals between federal herds to keep the gene pool wide.

Relationship with humans

For the peoples of the Great Plains the bison was food, shelter, clothing and tools, with more than 150 uses. The United States government backed the slaughter of the herds to break those nations. Crow chief Plenty Coups said the hearts of his people fell to the ground when the buffalo went away. Native Americans never domesticated the bison, and European attempts before the 20th century mostly failed. Ranchers describe a wild temper, and a good fence needs steel beams 6 metres long set in concrete.

Most bison today are raised for meat, hides and wool. About 35,000 were processed for meat in the United States in 2005, and Canada's farmed herd reached 195,728 head in 2006. The meat has less fat than beef and more protein. Bison draw visitors to the western parks, and Custer State Park keeps a public herd of 1,500.

Bison hurt more park visitors than bears do. In Yellowstone between 1980 and 1999, bison injured 79 people and bears injured 24. One person died from a bison goring in 1983. The animals look slow but outrun any person, and gunshots do not scare them.

In culture and myth

Many Plains nations hold the bison sacred. In Lakota tradition, White Buffalo Calf Woman brought the sacred pipe and the Seven Sacred Rites. The Sioux read the birth of a white calf as her return and a sign that prayers are heard. Among the Mandan and Hidatsa, the White Buffalo Cow Society was the most sacred society for women. The Lakota link the bison with Wi, the sun.

In many Plains stories the buffalo give themselves as food, so a hunter owes them respect and ceremony. Some peoples call the bison the first people. Other tales punish a hunter who treats the animal with contempt. During the slaughter, the Sioux and other nations danced the Ghost Dance to lift their spirits.

The bison appears on the buffalo nickel and on the seal of the Interior Department. Kansas, Oklahoma and Wyoming made it their state mammal, and Manitoba put it on the provincial flag. It sits in the arms of the Royal Canadian Mounted Police and on many sports jerseys. In 2016 the United States named it the national mammal.