roam and graze the spring grasses across the more than 40,000 acre Tallgrass Prairie Preserve in Pawhuska, Oklahoma.
American bison roam and graze the spring grasses across the more than 40,000 acre Tallgrass Prairie Preserve in Pawhuska, Oklahoma. © Morgan Heim for The Nature Conservancy

Stories in Oklahoma

Bison History and Facts

At one point, there were only about 1,000 bison left in North America.

Bison, A Furry History

Great herds of bison once roamed North America between the Appalachian Mountains on the east and the Rockies on the west. It is estimated that around 30 million bison roamed the continent when Columbus landed. The herds were so large that the bison became a symbol of the seemingly endless resources of the continent.

In the late 1800s, the bison were almost entirely eliminated, with less than 1,000 individuals left at the lowest point. A 1905 census indicated there were 835 wild bison and 256 bison in captivity at that time. Sanctuaries, zoos, and parks were safe havens for bison and helped to increase their numbers. The first national preserve for bison was founded in 1907 near Cache, OK and later became the Wichita Mountains National Wildlife Reserve. Subsequent game laws and other protective measures allowed the surviving bison to live and multiply.

Today their numbers have rebounded to about 350,000 - only about 1% of their original numbers, but enough so that the bison are no longer in danger of extinction. About 15,000 reside on public lands in the US, the rest are private herds, such as those maintained by The Nature Conservancy.

Bison at Wind Cave
Bison at Wind Cave A bison peers through the golden prairie grass. © Charles Larry
Bison calf at Tallgrass
Bison calf at Tallgrass First bison calf of 2020 at Tallgrass Prairie Preserve © Harvey Payne

Historically, the bison's most important predators were wolves. Wolves constantly followed the large herds, culling the old, incapacitated, and very young animals. Even solitary adult bulls were not immune to attack. Grizzlies occasionally killed bison, and mountain lions and coyotes were also occasional opportunistic predators of young calves. To a lesser extent, Native Americans were predators of the bison too. 

But one of the primary killers, before the slaughter by humans in the late 1800s, were iced-over rivers. Thousands of bison drowned, particularly in the northern U.S., when the enormous weight of crossing herds caused the ice to give way.

Since the wolf and grizzly bear are gone from the tallgrass prairie region, man is the remaining predator. The Nature Conservancy has no plans to reintroduce wolves to the Tallgrass Prairie. It isn't big enough and they wouldn't mix well with our neighbors' cattle.

Returning Bison to the Tallgrass Prairie

The Nature Conservancy reintroduced bison at the Joseph H. Williams Tallgrass Prairie Preserve in Oklahoma in 1993 as a critical part of the restoration of the tallgrass prairie ecosystem. Visitors to the preserve can usually see one or more small herds of bison by driving the 10-mile bison loop, though bison are constantly on the move and may be hidden by the rolling prairie terrain.

The Tallgrass Prairie bison herd was started with 300 animals donated by the Ken-Ada Ranch north of Bartlesville in the fall of 1993, and christened the Christina Adams Bison Herd (for the daughter of the Ken-Ada Ranch owners, Kenneth and Dianna Adams). The herd has since grown according to schedule and lives in over 24,000 acre fire-bison unit. The summer bison herd size is approximately 2,700 including calves and the over-wintering herd size is approximately 2,100.

Oklahoma Bison License Plate
Oklahoma Bison License Plate Oklahomans are supporting conservation with a Bison License Plate. © Courtesy/Oklahoma Tax Commission

Join the Herd!

Support bison conservation in style with this colorful license plate!

Managing A Herd

All heifer calves are vaccinated against brucellosis and all incoming animals are tested for brucellosis and tuberculosis and quarantined before admission to the herd. Even though there is no substantiated evidence of bison to cattle transmission of brucellosis, great pains are taken to ensure the herd remains brucellosis free. During the annual roundup all keeper animals are vaccinated for several bovine diseases and treated for external and internal parasites.

Bulls are sold at 6-7 years of age, since after this they tend to become more aggressive and dangerous. Cows are sold at 10-12 years of age. They are still productive through their early twenties but their sale value is higher as teenagers. Also, the older cows are less physically fit for withstanding the rigors of round-up.

The herd receives no supplemental feeding, but because the animals are in a restricted range, salt with trace minerals is provided. Water is available in creeks and ponds.

For research and record-keeping purposes, each individual bison in the herd is identified with an ear-tag transponder. This tag is read by holding a wand near the animal's head; the wand transmits the tag's data to a portable computer. Each transponder transmits a unique number, which is then assigned to that particular animal. Some of the information tracked includes the animal's sex, origin, age, weight, pregnancy status, and general health.

Bison at the Tallgrass Prairie Preserve at annually vaccinated against a variety of diseases.
Vaccination Bison at the Tallgrass Prairie Preserve at annually vaccinated against a variety of diseases. © David Smith

Fast Facts

  • Bison is the correct term for the mammals in North America. Their full latin name is bison bison bison.  According to scientists, true buffalo are confined to Africa and Southeast Asia. 

  • Before the settlements of modern civilization, around 30 million bison roamed across North America. By 1890, fewer than 600 plains bison were alive. 

  • Bison and cattle are cousins - they're both grazers (that is, they are in the same genus, Bos). 
 But bison are the largest native animals on the North American continent and can consume more than 30 pounds of grass (air-dry weight) in a day.

  • Full-grown bison bulls stand about 6.5 feet at the shoulder and can weigh up to 2,000 pounds. 

  • Bison prefer young, tender grasses and eat few forbs (such as wildflowers). Research at the Tallgrass Prairie Preserve has found that not less than 99% of a bison's diet is grasses and sedges.
  • The bison's rubbing on young trees helps prevent trees from invading the prairie.
  • When necessary, bison will travel a long way to find water; however they can go for long periods without it. They are powerful swimmers too, navigating with all but the hump, muzzle, and top of the head submerged. 
  • Bison can jump 6 feet vertically and because they reportedly can jump more than 7 feet horizontally, "bisonguards" on the Preserve are 14 feet wide. (This is double the standard width of a cattleguard.) 
Bison can also run speeds up to 35 miles per hour. 

  • Both males and females have horns; the cow's are just smaller. A bull bison can be identified from a cow by wider, thicker horns; a wider skull; and a generally more massive structure. 

  • The gestation period for bison is 9.5 months. 
Calves are generally born in the spring and weigh 30-40 pounds. 

  • Wallowing is practiced by both sexes and all age classes. Wallows are usually in dry areas, but wet areas may be used. This behavior seems to be important in grooming, sensory stimulation, alleviating skin irritation, and reproductive behavior. Wallows also serve as water reservoirs, making small ponds that become available to vertebrates and invertebrates for multiple uses; in addition, such ponds enhance growth of specific vegetation needing moist or wet habitat. Wallowing behavior also transports soils and seeds to other areas via their fur.
  • The bison was named the state mammal of Oklahoma in 1972 and the national mammal of the United States in 2016.
Bison Release - CBS - Oct 18, 1993 In the fall of 1993, 300 bison were released back to their home on the tallgrss prairie. And now it's time to celebrate 20 successful years of restoring a fully-functioning portion of the tallgrass prairie ecosystem with the use of free-roaming bison!

Vital Statistics

  • Bison are social animals and live in herds that change in size and composition throughout the year. In winter, herds are much smaller, typically only 20 to 30 in number, with older bulls completely isolating themselves. During the rut (mating) season in summer, bison gather in very large herds. Herds are definitely matriarchal with cows usually leading herd movement.
  • Bulls weigh from 1,600 to 2,000 pounds, stand between 5.5 and 6.5 feet high at the shoulder, and measure from 9.5 to 11.5 feet in total length (including the tail). Bulls seldom live longer than 20 years but, in rare cases, may live to be 40 years old. The cow is smaller, weighing up to 1,100 pounds, although most weigh about 1000 pounds. They stand 4.5 to 5.5 feet in height at the shoulder, and are less than 10 feet in length. Less shaggy on the head and chin, she has a smaller hump and her horns are more slender and curved than the bull's.
  • A bison's coat attains prime condition during the winter months, then sloughs off in clumps during the annual molt in the spring. The biggest chunks come from the hump and shoulders, where fur is two to five times thicker than the hair on the hindquarters. This difference in thickness accentuates the hunchback shape. The hair on forelegs, throat, chin, crown, and forehead reaches surprising lengths, especially on older animals. The longest masses, dangling from between the horns and upper forehead, have been known to grow to 22 inches.
  • Bison are subject to the same diseases as cattle but in the wild seem to be amazingly free of disease. No serious epidemics have been reported in present-day animals. Some animal breeders have tried to develop a hardy, useful kind of domestic animal by crossing American bison with ordinary domestic cattle. The cattaloes or beefaloes that result have not proven satisfactory, primarily due to infertility problems.