Close up of a bison's face.
Bison Tallgrass Prairie Preserve © Josie Briggs

Animals We Protect

American Bison (Buffalo)

Learn about the iconic American bison and see what we're doing to protect them.

Young bison calf surrounded by herd.
Young bison calf protected by the herd. © Morgan Heim

Bison Fast Facts

Common name: American bison, buffalo

Scientific nameBison bison

Conservation status: Near threatened, Population stable

Lifespan: 10 to 20 years

Weight: Adult Males: 1,000–2,200 lbs, Adult Females: 790–1,200 lbs, Calf: 30-70 lbs at birth

Meet the American Bison

The American bison takes the top prize for the largest land mammal in North America. Adult males weigh in at up to 2,000 pounds and stand as tall as six feet high at the shoulder.

These titans of North America are grazers, matriarchal-led family groups ranging from tens to thousands of buffalo. As they move across the prairie, they selectively focus on the grasses and sedges avoiding most of the forbs and legumes which helps balance the floristic competition. They sometimes wallow, which among many benefits helps mitigate biting insects and is also a social behavior thought to be a sign of contentment. These wallows create shallow depressions in the dense prairie which provide microhabitats to insects and amphibians among others to complete their reproductive cycles.

Adult males reach sexual maturity at six years old and females at three years old. They mate once each year beginning in July and lasting up to September. During the mating season, also called the rut, bulls (males) will fight aggressively by ramming their heads together and charging at one another for a chance to mate with a cow (female).

After a nine-month gestation period, cows will give birth to a single calf each spring. You can typically see mothers with young calves beginning in April.

It’s worth noting here that female bison weigh up to 1,000 pounds and run just as fast as the males at 40 miles per hour.

Bison are very protective of their young and as a group do their best to protect them from any dangers. When visiting a TNC preserve—or any preserve—where bison are present, it’s best to give them the space and respect they deserve, for your safety and for theirs. 

Adult female bison with a young calf.
Next Generation A bison calf with its mother at Cross Ranch preserve in North Dakota. © Richard Hamilton Smith
Lone adult bison at sunset on the prairie.
Bison Sunset at TNC's Cross Ranch preserve in North Dakota. © Richard Hamilton Smith

Wait…Are they bison or buffalo? 

Yes! Both terms have important scientific and historical meanings and use, and both continue to be used today to refer to the nation’s official mammal. There are also hundreds of words from Indigenous languages that have been used for thousands of years. Words like: “tatanka” or “pte” in Lakota or “yanasi” in Cherokee.

Genetically speaking, the American bison is not akin to either the water buffalo of Asia or the Cape buffalo of Africa. The American bison are found only in North America and certain parts of Europe.

Oceans apart in their range, the physical appearance of the American bison is vastly different from water buffalo and Cape buffalo. Developing on different continents means they encountered different conditions including climate, which influenced the evolution of their bodies and behavior.

Protecting the American Bison 

Millions of bison once lived and traveled across huge sections of the United States. You could see these icons of the prairie from Canada all the way south to Mexico and even as far east and west as the coasts.

But as American settlers developed and expanded, the U.S. government encouraged settlers to slaughter millions of these animals, bringing bison and the Indigenous communities that relied upon the herds to near extinction in the early 20th century.

At the end of this brutality, tribal communities were decimated, and less than 1,000 free-roaming bison remained in the world.

Today, about 500,000 bison live in the U.S. and can be found in all 50 states. However, most of these bison are privately owned and raised as livestock. Only a small fraction of this number includes bison who are living in conservation herds and even much less than that are bison who are roaming on large landscapes. There are no truly free-roaming bison left in North America. Fortunately.

The Nature Conservancy collectively is one of the largest bison producers with over 6,000 bison living on 12 preserves we own and manage in the United States.  

An adult bison watching a small group of birds.
Why Bison? Birds and buffalo go together. © Morgan Heim

Why Bison?

How does TNC work with bison to manage grasslands in the Great Plains?

Bison can be found grazing on 12 of The Nature Conservancy’s preserves across North America. At TNC, we consider grazing to be essential to the health of our native prairies and grasslands. Recognizing that most of our grasslands in North America evolved under the influence of climate, fire and grazing, we reintroduced bison to our first preserve in 1978 and continue to support bison across our 12 preserves to ensure those lands remain diverse and resilient. 

What does TNC bring to the table?

TNC has long been in the business of protecting our lands and waters. Across the Great Plains and beyond, we manage some of the highest-quality grasslands remaining in North America. It’s a little-known fact that native grasslands are one of the most endangered and least protected habitat types on Earth. Grasslands are also dependent on periodic disturbance, through grazing and fire to remain healthy and productive.

At TNC preserves, we manage bison herd sizes that support and enable healthy grasslands while also sustaining healthy bison. This careful balancing act ensures both bison and grasslands can thrive as conditions around us change. We also work with conservation partners like the National Park Service, Intertribal Buffalo Council, Tanka Fund, and other Indigenous organizations to transfer bison to support herds and communities around the country. 

What do fragmented grasslands mean for bison?

Prior to colonial settlement in North America, bison roamed freely across North America, undeterred by obstacles commonly found today like the privatization of land, fences, diseases brought in by exotic cattle and other livestock not native to this land, roads and buildings. Since that time, a lot has changed and the native grasslands that once blanketed much of central North America have dwindled to just a small fraction of their former range.

What this means for bison is that they no longer have the physical space needed to live and sustain herd sizes of the past and coupled with their classification by many states as “livestock, " they cannot roam freely as wild animals as they once did. 

How does returning bison to native grasslands affect the ecology of these landscapes?

The bison and grasslands of today are the result of a relationship that has evolved over the past 12,000 years. Bison help maintain grassland ecosystems in many ways. Bison provided the much-needed disturbance that healthy grasslands depend on, including their selective grazing, which created floristic balance and structure heterogeneity, nutrient recycling, wallowing, and many more. The relationship between fire and grazing is vital to creating a mosaic of habitats within the grassland ecosystem. Over thousands of years, this relationship aided in creating some of the most biologically diverse ecosystems on Earth. 

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Find a Bison Herd Near You

Visit one of these TNC preserves and watch the bison roam for yourself! Catch adorable cinnamon babies in spring or witness the thrill of the rut (from a distance) in fall.
Bison calves at Tallgrass Prairie Preserve.
Joseph H. Williams Tallgrass Prairie Preserve
This preserve is the largest protected remnant of tallgrass prairie left on earth.
Bison at Cross Ranch under rainbow and cotton candy sky.
Cross Ranch Preserve
North Dakota
TNC maintains bison herds in the central and south units of Cross Ranch, which can be viewed at a distance or from across fence lines.
Bison bull closeup.
Samuel H. Ordway, Jr. Memorial Preserve
South Dakota
TNC maintains a bison herd of about 250 animals in the central portion of the preserve. The herd can sometimes be viewed across the fence from the nature trail area.
Bison calf nursing.
Niobrara Valley Preserve
Niobrara Valley Preserve is one of the largest TNC preserves in the U.S., and a model for grassland management using bison, cattle and fire.
Bison closeup.
Broken Kettle Grasslands Preserve
Broken Kettle Grasslands is home to Iowa's largest remaining prairie and over 200 bison.
Bison calf on the prairie during fall.
Kankakee Sands Preserve
Today there are more than 70 bison at Kankakee Sands grazing on 1,100 acres of prairie, located both north and south of our Kankakee Sands Office.
Several bison grazing in a pasture under warm light.
Nachusa Grasslands Preserve
The bison roam across 1,500 acres of rolling land and may not always be visible. Be sure to bring binoculars and stay outside of the fenced bison unit.
Two calves and two adult bison grazing.
Dunn Ranch Prairie
There are more than 200 bison at Dunn Ranch Prairie – grazing on 2,300 acres of prairie. The two pastures are divided almost equally into two 1,100 units.
Bison in pasture with birds flying overhead.
Konza Prairie Biological Station
Konza Prairie is home to a range of wildlife from large grazing animals like bison to a multitude of insects, amphibians and reptiles.
Bison profile with a herd and sand dunes in the background.
Zapata Ranch
In the San Luis Valley, TNC has led an effort for more than 20 years to raise, manage and study a bison herd and learn from the animals’ interaction with the landscape.
Bison bull closeup.
Smoky Valley Ranch
Smoky Valley Ranch is home for a satellite herd of bison from Wind Cave National Park, to protect the rare genetics of the U.S. national mammal.
Bison closeup.
Tallgrass Prairie National Preserve
The U.S.'s only national park unit dedicated to the tallgrass prairie, privately owned by The Nature Conservancy and co-managed with the National Park Service.

Bison at The Nature Conservancy

Discover one of the most iconic species across 12 preserves at The Nature Conservancy.

BIson exiting the corral after a health check during annual roundup.
Adult male bison grazing alone in the grass.
Small bison herd in a haze.
BIson calf walking through lush green grass.
Four adult bison walking through snow at Cross Ranch in North Dakota.
Bison standing in the rain at Broken Kettle Grasslands Preserve in Iowa.
Two male bison ramming their heads together, fighting for a female.
Small herd of adult bison in the foothill of Colorado.
Adult female bison and her new calf.
Man standing on a flatbed truck in a herd of bison.

Support Bison and Grasslands Conservation

Grasslands are among the least protected and most endangered landscapes in the world. Give today to help TNC and our furry conservation partners further this important work.