The American Bison: A Nature Profile

A majestic bison roams the plains, a powerful symbol of North America's wild heritage

The American Bison (Bison Bison) is the largest land mammal in North America by weight, and is a symbol of strength, resilience, and cultural heritage. With bulls weighing up to 2,600 pounds and standing over 6 feet tall at the shoulder, the beautiful creatures move with ample grace across the open plains, grasslands, and river valleys that they call home. Once numbering in the tens of millions, bison were central to the cultures of many Native American tribes, providing food, clothing, tools, and cultural significance. Their overhunting and near extinction in the late 19th century represents a profound chapter in American history. Today, conservation efforts have helped restore bison populations, allowing these iconic animals to continue roaming the continent as living symbols of the American wilderness

Historical Context

Originally, French settlers in 1616 used the word Buffles as a name after seeing drawings and skins of the mammal, which derived from the Latin buffalus, a word used to describe an antelope, gazelle, or ox. Later, bison was taken from the French language, originally used to describe aurochs, an extinct species of bovine commonly thought to be the wild ancestor of domestic cattle. In Native American languages, there was no gender neutral term for the species, rather a specific word for bulls and cows. For example, in Arapaho, bii refers to a bison cow, and héécee refers to a bison bull. The lack of a gender neutral term in indigenous languages for an animal is not normal, and this anomaly in regard to bison is common across many different tribes. This is presumably a sign of how significant the bison is in Native American life and culture. The term bison and buffalo are commonly used interchangeably, however buffalo are a separate species to bison

Bison are members of the tribe bovini, more commonly known as bovine, and traditionally have been considered their own genus. There is some newer genetic evidence that suggests they fall within the bos genus, which contains many bovine, including wild and domesticated cattle. Bison first appeared in Asia 2.3 million years ago, in the form of the Siberian Steppe Bison, and 195-130,000 years ago migrated into North America by crossing beringia. Once coming to a new geographic environment, the species rapidly evolved, and the modern day American Bison emerged roughly 11,000 years ago

The range of the American Bison was enormous, they occupied the majority of North America, from as far north as modern day Alaska, all the way down to northern Mexico, and along the Atlantic Ocean. Their population estimates in the late 18th century ranged from 10 million to 60 million, with the latter being the more commonly cited figure. However, in the late 19th century, the United States aggressively hunted the bison herds, and at their lowest numbers, the continental bison population was estimated to be as low as 300 individuals. Through the 20th and 21st century, conservation efforts were enacted, and in 2017 the estimated continental bison population soared to 500,000. Due to this rapid decrease in population in the 19th century, Yellowstone National Park is the only place where bison have lived continuously since prehistoric times

Biology, Behavior, and Ecology

Description & Habitat

Bison have a shaggy, long, dark brown winter coat, and a lighter weight, lighter shade, brown summer coat. Bulls are significantly larger and heavier than the cows, with length measured head to rump coming in at 11.5' for bulls and 9.5' for cows. Their heights at the shoulder average 6.5' and 5' respectively, however their weight has a wider range. The median weight for bulls are between 1,600-2,200 pounds, with an upper extreme around 2,600 pounds. For cows, the median weight is between 990-1,100 pounds, with an upper extreme around 1,400 pounds. The heaviest wild bull ever measured reached 2,800 pounds, however there have been estimates of wild bulls being over 3,000 pounds. When raised in captivity, bison can achieve unnaturally large weights. The heaviest semi domestic bison was recorded at a whopping 3,801 pounds. Both sexes have short, curved horns that grow up to 2' long with 3-4' of width, which they use for fighting status within the herd and during rut. Bison also have a large hump on their shoulders connecting to their next. This hump consists of large, tough muscles that allow bison to graze all day long, and swing their heads side-side to clear away snow drifts

Wood Bison (top) vs Plains Bison (bottom)

There are two subspecies of American Bison described, the Wood Bison, and the Plains Bison. The wood bison is generally larger, with a more square hump, dark, wooly coats with less fur on the forelegs, larger horn cores, large, triangular heads with less defined shoulder capes, and have adapted to more northern climates. The plains bison is generally smaller, with a more round hump, shorter and shaggier hair, short, backward arcing horns, massive heads with short noses and shaggy capes, and are adapted to prairie grasslands and hills. While superficially similar to the European Bison, the American Bison do have differences with their European counterparts. The American Bison is heavier, but more rangy, leading it to be slightly smaller at the shoulder. American Bison graze more and browse less due to how their necks are set, and the horns of the European Bison point forwards through the plane of their face, making it more adept at fighting by interlocking horns, while their American counterparts prefer charging

The typical habitat for bison is open or semi open grasslands, as well as sagebrush, semi arid lands, and scrublands. Some lightly wooded areas have also been known to support bison, especially in the fall season. Bison will also graze in hilly and mountainous areas where the slopes are not too steep. They are not typically known as high altitude animals, but the Yellowstone Park herd is frequently found above 8,000' elevation, and the Henry Mountains herd is found at 10,000' elevation in Utah. Nowadays, bison are mainly found in national parks and reservations, as well as private herds. Through reintroduction efforts, there are now some free roaming bison herds outside of reserves in Utah

While often secure from predation due to their size and strength, in some regions vulnerable individuals are regularly preyed on by wolves. Wolf predation typically peaks in late winter, when elk have migrated south and bison are distressed with heavy snow and shortages of food sources. Attacks typically focus on weak and injured cows, as well as calves. Wolves actively target herds with calves more than those without. Healthy, mature bulls almost never fall prey. The length of a predation episode can vary, ranging from a few minutes to several hours. Bison calves use five apparent defense strategies to protect themselves from wolves: running to a cow, running to a herd, running to the nearest bull, running in the front and/or center of a stampeding herd, or entering a river, lake, or other body of water. When fleeing, cows with calves typically take the lead, while larger cows and bulls take to the rear to guard the escape. Grizzly bears are known to feed on carcasses, and may steal a wolf's kill. Grizzlies can sometimes kill calves, as well as older, sick, or injured adult bison, but direct killing of an adult bison is very rare, even when targeting lone or injured individuals. Bison have a life expectancy of 15 years in the wild, and up to 25 years in captivity. Some herds in Canada have seen males and females reaching 22 and 25 years old respectively

Bison are one of the most resplendent and alluring members of the national parks, and their lethargic movements often cause people to mistake them as docile and slow. However, the American Bison is one of the most dangerous animals to visitors of national parks, and will attack humans if provoked. While appearing slow, they can run up to 35-45 mph, and jump over 6'. Bison may approach due to curiosity, however close encounters, including touching animals, may lead to dangerous situations. Between 1980 and 1999, 79 people were charged and injured by bison, leading to injuries that ranged from broken bones and goring puncture wounds, to abrasions and bruises. In that same period, bears only injured 24 people. Of the 79 injured by bison, only one had injuries that led to death

Behavioral & Social Practices

Bison are a migratory species that typically live in herds. Female bison live in maternal herds with other adult females and their offspring. Males will leave their herds once they reach sexual maturity and either live alone, or join a herd of other male bachelors. In some cases, female herds will contain a few adult males. The sizes of these bull only herds range from just a few individuals, up to 30. Meanwhile, the primarily female herds, including offspring, average around 20 individuals in the winter, but can increase to an average of 200 in the summer, and have even been seen to get as large as 1,000 individuals during their breeding season called rut.

While in their herds, they have typical daily movements, averaging 2 miles traveled per day. The range of these movements seem to be influenced by seasonal vegetation changes, introspection and size of foraging sites, the rut, prevalence of biting insects, size of the preserve, and the availability of water. Their lifestyle consists of 2 hour periods of grazing, resting, and cud chewing, and then they move to a new location to repeat the cycle. A need to graze more is part of the reason bulls split away from the female herd once they reach sexual maturity, as they need to consume enough energy to support their larger builds. Bison typically graze for 9-11 hours a day, feeding primarily on grasses, sedges, and other grass-like plants in open grassland and meadow communities. They also eat forbs and browse, however these combine for roughly 10% of their diet. Bison have multi chambered stomachs that include various microorganisms to break down and digest plant material. Bison alternate between eating and ruminating, which is the process of regurgitating partially digested food and chewing it again to aid in digestion. Their large digestive tract allows them to digest low quality foods with greater efficiency than other ungulates such as cattle, elk, or deer

Rut is the mating season for American Bison, which occurs from late June to September, however most of the breeding is done between July and August. During rut dominant bulls will maintain a small harem of cows, "tending" to them by following them around and chasing away rival males. The tending bull will block the cow's vision by standing in front of them, so she will not see any rival males. A challenging bull may bellow or roar to get the female's attention, to which the tending bull must bellow or roar back. The most dominant males will mate within the first 2-3 weeks, while subordinate bulls will mate with any remaining estrous cows that have not mated yet. To establish dominance and ward off challengers, bulls engage in various behaviors, such as bellowing, wallowing, charging, and head butting. While this can be a dangerous time for bulls, they rarely fight to the death

After conception, bulls play no part in raising the calf. The gestation period for the cow averages 285 days, almost the same as a human. Between April and June, cows will leave the herd for the birthing process, which can take anywhere from a few minutes to several hours. At birth, calves are 40-50 pounds, and a reddish, cinnamon color. Within minutes of being born, calves are standing and ready to feed on the nutrient rich colostrum milk. After feeding, they are ready to move with the herd. Within a week they will start mimicking their mother's behavior and nibble at the grass. At 2 months of age, they begin forming shoulder humps and horn buds. They are typically weaned off of their mother's milk by 7-9 months of age.

Bison become sexually mature at 2 years of age. At this time, bulls will break away from their maternal herd to venture alone, or join a herd of fellow bachelor males. Cows will begin mating during their first rut, however most bulls are 5 years old by the time they first breed. This is because while sexually mature at 2 years old, they are not as physically developed as the more mature bulls, and fail to compete against them. Cows will breed for their whole lives while males will typically do most of their breeding between 5 and 10 years of age. Before 5 years of age, and after 10 years of age, bulls aren't dominant enough to challenge the bulls in their prime, and mate substantially less

A bison calf staying near their mother

Dominance hierarchies take place amongst bison herds, and their dominance is directly linked to their birth dates. The earlier in the generation a bison is born, the more dominant they are. In addition to dominance, the older bison of a generation have higher fertility rates in comparison to the younger ones. This is likely due to fitter, more dominant bulls outcompeting subordinate males in the rut and mating with whom they choose early on in the season. Bison have also been observed to engage in homosexual behaviors, males much more so than females. In the case of males, it has been stated this behavior is unlikely to be dominance related, but rather for social bonding and sexual experience

During the summer months and rut, bison tend to move out to wide open plains. During the fall and winter, they tend to

gather in more wooded areas. During these winter months, bison engage in horning behaviors. They rub their horns up against trees, young saplings, and even utility poles. Aromatic trees like cedar and pine tend to be preferred. The prevalence of this behavior has a positive correlation with insect population, so researchers believe this is a method of defense against biting insects. Bison also engage in wallowing behavior, as seen to the left. This is when bison roll around in a shallow depression in the ground, covering themselves with dirt and mud. Past and current hypotheses explain the purposes of this behavior include grooming associated with shedding, male-male interaction typically during rut, social behavior for cohesion, relief from skin irritation due to biting insects, reduction of ectoparasite load, and thermoregulation. Bison wallowing also has important ecosystem engineering effects and enhances plant and animal diversity in prairies

Bison-Human Relations

Significance in Native American Society

The American Bison played a critical role in the lives of Native Americans indigenous to the Great Plains Region. They were a massive resource, and fundamental to their livelihoods. Tribes used the products of a bison kill for up to 150 different purposes. The bison hides were used for shields, saddles, moccasins, and tipi walls. They were able to use the fur to make sturdy ropes, stuffing for pillows, and warm robes. The bones were used as tools, weapons, and ceremonial adornments. The brain could be used in the preparation of hides. The stomach lining was used as a cooking vessel, with its contents used for medicinal purposes. The Native Americans of the area deeply respected the bison, and made sure to have functions for every part of the animal. Despite its importance to their culture and survival, Native Americans never attempted to domesticate bison

Native Americans, and later on pioneers, relied on paths naturally created by bison. Bison would continually follow the route of least resistance, following watersheds and the crests of ridges to avoid muck and snowdrift, creating trails by repeatedly stomping their hooves into the ground. These trails were characteristically north and south, but occasionally east to west. These trails were followed by Native Americans as routes to hunting ground, and as warrior paths. These trails were invaluable to explorers and were adopted by many pioneers. Several of these trails, particularly east to west ones, later became the routes for railways, as the bison blazed the easiest path through various challenging terrains

Along with the physical advantages of having bison, Native Americans had a substantial religious and sacred connection with the animal. Each tribe had their own special relationships with them. Some tribes thought of bison as their brethren, believing they were the first humans born. Some believed bison emerged from sacred waters, or from the earth. Others saw bison as a symbol of life, existence, and hope, believing bison to be relatives, and a part of them. The Sioux believe that the birth of a white buffalo was the return of the White Buffalo Calf Woman, their primary cultural prophet and bringer of their "Seven Sacred Rites". Among some tribes, the White Buffalo Cow Society was one of the most sacred societies for women

The reduction of the bison population heavily affected the surrounding Native American tribes. The concept of extinction was foreign to many tribes, as they had always managed an ecologic balance amongst the wildlife. Apart from losing one of their most valuable resources, Native Americans were also losing one of their most sacred spiritual symbols. Aspáalooke chief Plenty Coups was quoted saying "When the buffalo went away, the hearts of my people fell to the ground, and they could not lift them again. After this, nothing happened. There was little singing anywhere."

Population Culling Effects & Restoration Efforts

The story of the American Bison is not complete without the story of the continental culling and

following restoration efforts. During the 1800s, the United States were building a railway that traversed

across the Great Plains. This railroad created a continental divide amongst the bison population. While the railroad was being built, workers hunted the bison for food. At the same time, European settlers wanted to hunt the bison for their tongues and hump (which were considered a delicacy), as well as their hides and bones, using little else from the animal, often just leaving everything else to decay in the grasslands. On top of this, the US government encouraged the elimination of bison, as it was the Native Americans primary food source in the area. The strategy was to kill off the buffalo population, and drive the natives up north into Canada. Columbus Delano, Secretary of the Department of the Interior in the early 1870s stated, "Every buffalo dead is an Indian gone. The rapid disappearance of game from the former hunting grounds must operate largely in our favor to confine the Indians to smaller areas, and compel them to abandon their nomadic customs". Railway owners also sought the elimination of bison, as they would often cross the tracks causing delays. The image seen above is a real, historical photo of a man standing in front of a mountain made from bison skulls.

As a result of a combination of railroad workers seeking food, European settlers seeking trade commodities, railroad owners seeking more efficient transport, and the US government seeking the elimination of Native American tribes from the area, there was a devastating blow to the bison population. The estimated population of bison in North America prior to the 1800s was 60 million individuals, by the late 1800s, there was estimated to be less than 300 individual bison on the continent. That's a decrease of 99.9995%. A catastrophic decrease in population that nearly made the species extinct, and lead to a substantial genetic bottleneck that affects the species to this day

Some private citizens began to independently capture and shelter bison from being hunted in the late 1800s. In 1905, William Hornaday founded the American Bison Society and named US President Theodore Roosevelt as the honorary President. Roosevelt used his power as president to secure lands, procure buffalo from ranchers, and promote bison reintroduction projects. This marked an important turn of events for the continental bison population and governmental protection of them.

The Goodnight Herd

There were 7 primary herds that were utilized to reestablish the bison population. Five of these herds were privately owned, one was owned by what is now known as the Bronx Zoo, and an additional herd was present in Yellowstone National Park. One of the privately owned herds is now known as the Texas State Bison Herd, which has a founding population of only 5 bison. This herd was created by Charles Goodnight, who caught 5 wild calves in the 1880s. By the 1920s, the herd had grown to a population of over 200 individuals. Following Goodnight's passing in 1929, the herd was handed off between multiple different handlers, and by the time it was donated to the State of Texas in 1997, it comprised 36 individuals, all descendants of the original 5 claves. This herd in particular became a very monumental case study to analyze the results of a population bottleneck and the lack of genetic diversity within a population. The continuously low population of this isolated herd allowed for genetic drift to have a large effect, and the loss of genetic diversity was estimated to be around 30-40%. This lack of genetic diversity is credited with causing a rate of 0.367 offspring per female and a first year mortality rate of 52.6% between 1997-2002. Over that same 5 year period, the national rates were 0.560 offspring per female, and 4.2% first year mortality rate. The bottleneck and lack of genetic diversity caused the bison to become less fertile and less fit. Had conservationists not interfered, the Texas State herd likely would have gone extinct

Through the 1900s, these herds were protected and regularly mixed to increase genetic diversity. The growth of the populations within these herds allowed for reintroduction of bison into various state reserves and national parks. The US Department of the Interior has been a large factor in reestablishing the bison population, personally managing 17 different herds in 12 states, including Alaska. Private herds increased in numbers as well, as domestication of bison became a more common practice. As of 2017, there were an estimated 500,000 bison in North America, with roughly 30,000 living in public and private herds, and over 400,000 being raised as livestock. Reintroductions have seen bison begin to reclaim their historical range, having been reintroduced as far east as Indiana, as far north as Alaska, and as far south as Northern Mexico

Native Americans have played a large role in the reintroduction and conservation of American Bison in recent history. In 1990, the Inter Tribal Council was formed, consisting of 56 tribes across 19 states. These tribes have a collective herd of over 15,000 individuals, and focus on reestablishing herds on tribal lands in order to promote culture, revitalize spiritual solidarity, and restore the ecosystem. Some members argue the bison's economic value is one of the main factors driving its resurgence

One of the reintroduction efforts utilizing American Bison has been in Siberia. While American Bison are not endemic to Siberia, they are the closest extant relatives to the extinct Steppe Bison, who lived there during the Pleistocene Era. There is currently a conservation project of Pleistocene Rewilding in Siberia, which is the practice of reintroducing extant Pleistocene megafauna to the area, or introducing ecologically equivalent megafauna to restore a self functioning ecosystem. For this project, American Wood Bison were brought into Siberia from Canada, a total of 120 introduced from 2006 to 2020. Over 100 bison have been born in Siberia as of 2019, and the repopulation efforts have been mostly successful. A second herd of 10 juveniles was formed in 2020, and the American Wood Bison was officially registered the Yakutia Red List, naming it an official endangered and protected species

As a result of population culling, there is a small percentage of genetically purebred bison remaining in the world. Many bison were bred with domestic cattle to increase populations, and in attempt to create a stronger species. When crossbred, only the female offspring are fertile, and male offspring cannot become fertile until they are at least 7/8ths domestic cattle or bison. The crossbreeding with domestic cattle has resulted in only 4% of the current bison population to be genetically pure, and not contain DNA from domestic cattle

Domestication

Early domestication attempts of American Bison by European settlers often resulted in failures. Bison are a surprisingly challenging animal to domesticate, due to their incredible physical features. They were described as having a "wild and ungovernable temper". They can jump up to 6' high, and run 35-45 mph when agitated. Their agility and speed, combined with their great size and weight, makes bison difficult to confine, as they can easily escape or destroy most fencing systems, including razor wire. The most effective way to contain them is a fencing system involving large, 20' fences made from welded steel beams sunk at least 6' into concrete. These fencing systems, while costly, require very little maintenance.

Bison have become domesticated for their meat, hide, wool, and dairy products. The majority of bison in the world (roughly 400k) are being raised for human consumption and fur clothing. Bison meat serves as a low cost substitute for beef, while having higher protein, lower fat, and lower cholesterol. Bison meat essentially retains most of the flavor profile of beef, while having a stronger nutritional profile.

How to Enjoy and Help

Nowadays, if you want to see and enjoy this incredible animal, the most popular destination is the expansive Yellowstone National Park in Wyoming, Montana, and Idaho, the only place where bison have continuously lived since prehistoric times. Other popular destinations are Theodore Roosevelt National Park in North Dakota, and Grand Canyon National Park in Arizona. Bison are viewable to the public across more than 20 Department of the Interior managed lands, and in a number of Native American reservations, as well as other private properties.

The best time for bison viewing is generally July-August, as this is the peak of their rut and will have the most activity and largest herd numbers. If you want to catch a glimpse of some newborn calves, aim for March-May. Just remember to maintain a respectful distance from these enormous animals, the American Prairie Reserve recommends a distance of 300', and always ensure you are following the rules, regulations, and recommendations of the park or reserve you are visiting.

Bison are no longer considered endangered in the United States thanks to the conservation efforts enacted throughout the past century. However, the species does face other challenges, primarily due to the loss of genetic diversity from the species bottleneck. A low level of cattle gene introgression is present in most, if not all, bison herds. You can help the genetic restoration efforts by advocating to local and federal politicians, as well as donating to organizations that work to protect wildlife and natural resources, such as the National Wildlife Federation and the World Wildlife Fund.

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