American bison

• 1. Introduction

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  The American bison, Bison bison, once numbered an estimated 60 million individuals across North America. That figure is almost impossible to picture: a living mass so vast it darkened the horizon, stretching from Alaska south to the Gulf of Mexico and east nearly to the Atlantic tidewater. Then, in roughly a decade during the 1870s, the species was driven to the edge of oblivion. By 1889, only 541 animals remained in the United States. How did the largest land herbivore on the continent fall so far, so fast? And how did a handful of ranchers, Indigenous nations, and park managers pull it back from almost certain extinction? Those questions sit at the heart of the American bison's story.

• 2. A Deep Past

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  Bison first appeared in Asia around 2.6 million years ago, during the Early Pleistocene. They did not reach North America until between 195,000 and 135,000 years ago, crossing through Beringia from the Siberian steppe. Their ancestor, Bison priscus, gave rise to an extraordinary radiation of new species on the continent, including Bison latifrons, the longest-horned bison ever known. The arrival of bison is considered significant enough to define a named chapter in North American prehistory: the Rancholabrean faunal stage.

  Modern American bison are thought to have evolved from an intermediate species, Bison antiquus, at the boundary between the Late Pleistocene and the Holocene. Genetic analysis has placed bison within the genus Bos, making them closer relatives of domestic cattle and yaks than their distinct appearance might suggest. The mitochondrial DNA of their European cousin tells a slightly different story, however, indicating ancient mixing with aurochs or domestic cattle somewhere in that lineage.

  By around 9000 BC, the species occupied what researchers call the great bison belt: a sweep of rich grassland running from Alaska to the Gulf of Mexico. Sightings near Buffalo Ford on the Catawba River in North Carolina were recorded as late as 1750, evidence of just how far east the species once ranged.

• 3. Built for the Plains

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  Two subspecies exist today. The plains bison is the smaller of the two and carries a more rounded hump; the wood bison, found in boreal regions, carries a taller, squarer hump and is among the largest wild bovids on earth, surpassed in size only by the Asian gaur. The heaviest wild plains bison on record weighed 1,270 kg, while the largest semidomestic bison raised in captivity reached 1,724 kg.

  Bison are grazers above all else. On mixed prairie, cool-season grasses and sedges make up 79-96% of their diet. Their daily rhythm involves two-hour cycles of grazing, resting, and cud-chewing before moving to fresh ground. In the Hayden Valley in Wyoming, bison average about 2 miles of travel per day during summer.

  Social life is strictly organized. Females live in maternal herds with their young; males leave around age three to join bachelor groups or live alone. The two sexes reunite only during the breeding season, which runs from July through September. Dominant bulls shepherd small harems, physically shielding cows from rival males by blocking their line of sight. A bison's rank is tied to its birth date: calves born earlier in the season tend to be larger and more dominant as adults, allowing dominance itself to be inherited across generations. Gestation lasts 285 days, and a calf nurses for at least 7 or 8 months, with life expectancy in the wild reaching around 15 years.

• 4. The Near Extinction

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  Crow chief Plenty Coups described what the slaughter meant to his people in plain words: "When the buffalo went away the hearts of my people fell to the ground, and they could not lift them up again. After this nothing happened. There was little singing anywhere." That loss was not accidental. The U.S. government actively encouraged the destruction of bison herds as a strategy in the American Indian Wars, targeting the central resource of Plains Nations whose entire way of life depended on the animal.

  Indigenous peoples of the Great Plains had identified more than 150 uses for every part of the bison: food, hides for clothing and shelter, bones and horns for tools, and materials for ceremony. For some Plains peoples, bison are spoken of as the first people. The concept of a species going extinct was foreign to many tribes, which made the deliberate slaughter all the more devastating as a cultural and spiritual rupture.

  Commercial hunters accelerated what the government encouraged. The plains bison population collapsed through the 1870s and into the 1880s, dropping from an estimated 5.5 million in 1870 to 395,000 by 1880, and then to just 541 by 1889. What survived were a handful of animals scattered across six tiny herds, five of them held by private ranchers and one by the New York Zoological Park, now the Bronx Zoo. A separate wild group of 25 individuals clung on inside Yellowstone National Park.

• 5. The Genetics of Survival

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  Those six founding herds carried a combined effective population size estimated at between 30 and 50 individuals, from which every living plains bison today descends. The Texas State Bison Herd, also called the Goodnight herd after its founder Charles Goodnight, illustrates how extreme that bottleneck could be. Goodnight established the herd in the mid-1880s with five wild-caught calves. By 1887 it had grown to 13 animals; by 1910, to 125; and by the 1920s, to somewhere between 200 and 250. Then Goodnight died in 1929, the herd changed hands repeatedly, and its numbers became unknown until the state of Texas received it in 1997 with just 36 individuals.

  Researchers found the Goodnight herd's genetic diversity was strikingly low. The average number of alleles per locus was only 2.54, compared to 4.75 in the Yellowstone herd and 4.15 in the Theodore Roosevelt National Park herd. The heterozygosity level, a direct measure of genetic diversity, was 0.38 in the Texas herd versus 0.63 in Yellowstone. First-year calf mortality ran at 52.6% from 1997 to 2002, compared to 4.2% in healthier herds. A population model published in 2004 put the Texas herd's chance of extinction within 41 years, without new individuals, at 99%.

  Conservationists intervened. Simulations showed that introducing just 3 to 9 outside males would lift that herd's survival odds to 100% over the next 100 years. The Yellowstone herd followed a parallel trajectory: in 1902-18 females from the Pablo-Allard herd and 3 males from the Goodnight herd were brought in, pushing the effective population size to an estimated 7.2 individuals. Those founders contributed between 60 and 70% of the genetics of the Yellowstone herd as it stands today, a herd now numbering around 5,900 animals as of summer 2022.

• 6. The Contamination Question

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  During the bottleneck, several ranchers crossed surviving bison with domestic cattle in an effort to produce hardier animals they called "cattalo" or "beefalo." The offspring were difficult: only the female hybrids were fertile in the first generation, and the crossbred animals showed no hybrid vigor, so the practice was abandoned. The genetic legacy proved more durable than the practice itself.

  A landmark study by James Derr of Texas A&M University found cattle genes distributed throughout most national, state, and private bison herds. The proportion of cattle DNA in introgressed herds is typically quite low, ranging from 0.56 to 1.8%, but it is pervasive. As of 2011, while roughly 500,000 bison existed across private ranches and public herds, estimates suggested only 15,000 to 25,000 of those were genetically pure. The Yellowstone herd, the Henry Mountains herd in Utah, the Wind Cave herd in South Dakota, and the Wood Buffalo National Park herd in Canada are among the significant public herds that appear to have avoided cattle hybridization.

  One complicating factor is that mitochondrial DNA testing, the standard tool for decades, only traces the maternal line and says nothing about male-line contributions. This means the true scope of hybridization may be wider than any current count reflects. In response, the National Park Service and the Department of the Interior announced the 2020 Bison Conservation Initiative on the 7th of May, 2020, which aims to transfer up to three bison every five to ten years between Interior herds to shore up the genetic diversity of the overall population.

• 7. Sacred Symbol, National Mammal

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  University of Montana professor S. Neyooxet Greymorning, who teaches anthropology and Native American studies, described the bison's place in tribal life this way: "The creation stories of where buffalo came from put them in a very spiritual place among many tribes. The buffalo crossed many different areas and functions, and it was utilized in many ways. It was used in ceremonies, as well as to make tipi covers that provided homes for people, utensils, shields, weapons and parts were used for sewing with the sinew."

  Among the Sioux, the rare white bison is understood as the return of White Buffalo Calf Woman, the primary cultural prophet credited with delivering the Seven Sacred Rites. The Mandan and Hidatsa held the White Buffalo Cow Society as the most sacred of women's societies.

  Formally, the United States recognized the animal's significance in 2016, when the American bison became the national mammal of the country. The bison had appeared on the "buffalo nickel" from 1913 to 1938, and later featured on the Kansas, North Dakota, Montana, and Yellowstone National Park quarters. Kansas, Oklahoma, and Wyoming each list the bison as their official state mammal; in Canada, it is the official animal of Manitoba and appears on the coat of arms of the Royal Canadian Mounted Police.

  The Inter Tribal Bison Council, formed in 1990, brings together 56 tribes across 19 states and manages a collective herd of more than 15,000 bison. Its members argue that restoring bison to tribal lands rebuilds not just an ecosystem but the cultural and spiritual foundation of Plains life, while also offering a practical economic alternative to cattle for communities in the Plains region.