American Bison

About the American bison

The American bison, also called the American buffalo or simply buffalo, is a species endemic to North America and one of only two living bison species, alongside the European bison. It is the national mammal of the United States. Its historical range, dating to around 9000 BC, is known as the "great bison belt" — a stretch of rich grassland running from Alaska south to the Gulf of Mexico and east to the Atlantic Seaboard, reaching as far north as New York and south into Georgia, with some sources placing sightings as far south as northern Florida and as late as 1750 in North Carolina.

Two subspecies or ecotypes are recognized: the plains bison, which is smaller and has a more rounded hump, and the wood bison, which is larger with a taller, square hump. The wood bison is among the largest wild bovids on Earth, second only to the Asian gaur, and wild American bison can weigh up to 1,270 kg (2,800 lb), making the species among the heaviest land animals in North America and the heaviest herbivore on the continent. Bison have a shaggy, long, dark-brown winter coat and a lighter, lighter-brown summer coat, with massive heads and forequarters. Both sexes carry short, curved horns — up to 60 cm (2 ft) long with a 90–124 cm (3–4 ft) spread — used in status fights within the herd and in defense. Males are significantly larger than females: head-rump length reaches up to 3.5 m (11 ft 6 in) in males and 2.85 m (9 ft 4 in) in females, with heights at the withers of 186–201 cm (6 ft 1 in–6 ft 7 in) across the two subspecies. Typical weights run from 318 to 1,179 kg (701–2,599 lb) in males and 360 to 640 kg (790–1,410 lb) in females, though the lowest figures likely reflect younger animals around the age of sexual maturity, at two to three years old.

Once numbering an estimated 60 million animals in the late 18th century, the species was reduced to just 541 individuals by 1889 through a combination of commercial hunting, slaughter, and disease introduced from domestic cattle — a collapse that was also part of the broader effort to destroy the traditional way of life of Native Americans on the Great Plains, for whom bison were a central resource for food, shelter, and tools. Recovery efforts starting in the mid-20th century brought the wild population back to roughly 31,000 by March 2019.

Behavior and diet

Bison are herbivores that graze on the grasses and sedges of North American prairies. Their daily routine follows a pattern of roughly two-hour periods of grazing, resting, and cud-chewing, after which the herd moves on to graze somewhere new. Sexually mature young bulls may attempt to mate with cows as early as two or three years old, but where more mature bulls are present, they typically can't compete successfully until they reach about five years of age. Calves are lighter in color than adults for their first two months of life, and — though extremely rare — white bison do occur.

American bison differ from their European relatives in several behavioral ways. They graze more and browse less, thanks to a differently set neck, and their horns point differently than the European bison's — American bison favor charging in confrontations, while European bison lock horns more like domestic cattle. American bison are also more easily tamed and breed more readily with domestic cattle, which led ranchers in the aftermath of the 19th-century population collapse to crossbreed some animals into "cattalo" or "beefalo." That practice was eventually abandoned because the crossbred animals showed no hybrid vigor, and only the female offspring of such crosses were fertile. Today the U.S. National Bison Association's code of ethics prohibits members from deliberately crossbreeding bison with other species, and ranchers commonly use DNA testing to identify and remove residual cattle genetics from their herds.

Range and habitat

American bison live in river valleys and on prairies and plains, favoring open or semi-open grasslands as well as sagebrush, semiarid lands, and scrublands; some lightly wooded areas have historically supported them too. Bison also graze in hilly or mountainous country where slopes aren't too steep — the Yellowstone Park herd is frequently found above 2,400 m (8,000 ft), and the Henry Mountains herd in Utah ranges up to 3,000 m (10,000 ft) in mountain valleys.

Population estimates from 2010 put the total number of American bison between 400,000 and 500,000, with about 20,500 in 62 conservation herds and the remainder in roughly 6,400 commercial herds. The IUCN considers only about 15,000 bison to be truly wild, free-ranging animals not primarily confined by fencing. The species' historic southern range extended into northern Mexico, and reintroductions there — including to the Janos Biosphere Reserve in Chihuahua in 2009 and Maderas del Carmen in 2020 — have added to the Mexican bison population, supplementing a herd that has moved between Chihuahua and New Mexico since at least the 1920s. Bison have also been reintroduced to conservation land in the eastern United States, including an easternmost herd established at Kankakee Sands in Indiana in 2016, and a population of wood bison has been introduced to Yakutia, Russia, since 2006 as a rewilding effort.

Conservation status

The American bison is listed as Near Threatened on the IUCN Red List, based on a 2017 assessment. The species nearly went extinct in the 19th century through commercial hunting and slaughter, combined with bovine diseases introduced by domestic cattle, collapsing from an estimated 60 million animals to just 541 by 1889.

Recovery efforts that began in the mid-20th century have rebuilt the population to roughly 31,000 wild bison as of 2019, though for many years the species survived mainly in a handful of national parks and reserves. Population estimates from 2010 put the total, including commercial herds, at 400,000 to 500,000, but only about 15,000 bison are considered truly wild, free-ranging animals not primarily confined by fencing. DNA from domestic cattle has also been found in almost all bison herds that have been examined, a legacy of past crossbreeding.

Today, reintroductions have allowed bison to roam freely again in parts of the United States, Canada, and Mexico, while other populations are kept in smaller conservation herds or on private commercial ranches. Groups such as the Nature Conservancy have returned bison to more than a dozen U.S. nature preserves, and in 2014 U.S. tribes and Canadian First Nations signed a treaty supporting bison restoration, the first such agreement in nearly 150 years.