Close-up, bison are as intimidating as they are awe-inspiring. Their larger-than-life stature towers over everything around them; their shaggy coats are thick and textured; their enormous heads draw your eye with their lumpy, irregular shape. But even though bison are known as quintessential to North America, their existence today is not as wild as their reputation.
Before European contact, North America from Alaska and Canada to Mexico and from eastern California to Virginia were home to bison. However, the Great Plains of central North America was home to the majority of the estimated 30 million bison. Due to exotic disease and overhunting by white settlers, these animals were driven nearly to extinction by the late 1800s.
Today, their numbers have rebounded to around 350,000 animals, thanks to hunting laws, protective measures, and conservation efforts by the American Bison Society and now including work by The Nature Conservancy. However, they are still considered ecologically threatened as a wild species through most of their historic range, since most herds today are heavily managed, and they no longer roam across the grasslands as they once did.
In Colorado’s San Luis Valley, The Nature Conservancy has led an effort for the past 20 years to raise, manage and study a bison herd and learn from the animals’ interaction with the landscape.
Bison Are a Keystone Species
Bison need grasslands as much as grasslands need bison. They are a keystone species on the plains because they help create habitat for many species, including grassland birds and native plants. As bison graze, they aerate the soil and plant seeds with their hooves which aids in plant growth. They also disperse native seeds, maintaining a functional and balanced ecosystem. By grazing, bison shape the species and structure of plant communities, which in turn provide specific habitat for other species.
In Colorado, bison once roamed over most of the state. Today, they only live in managed herds. More than 20 years ago, the Nature Conservancy protected the Medano and Zapata Ranches in the San Luis Valley. We also helped the neighboring Great Sand Dunes become a national park. In 2001, we acquired a bison herd on the Medano Ranch, with a goal of providing a place where bison could interact with the land as research suggests they did in the past.
This herd of around 1,600 animals has helped advance research and conservation for bison around the country. TNC and our partners decided to try and manage the herd like wild animals—allowing them to range freely within the 44,000-acre ranch, choose where and what to graze, and have enough males that females could be selective in their breeding partners.
The San Luis Valley has a rich history of bison and people who relied on them. Ancient bison relatives have been found in the valley, including the Bison antiquus, an animal that had 3-foot horns and weighed 3,500 pounds. From the earliest written records of the Spanish conquistadors, the valley was home to herds of bison and their co-inhabitants, the Ute Tribe.
Today, the high desert terrain and water resources on the Medano Ranch allow for extremely healthy bison. Unlike many managed herds, they don’t depend on supplements or irrigated water.
“We work with USGS and the National Park Service to collect data to see how the bison move through the ranch and use vegetation,” says Cat Kelly, Colorado land steward. “They practice self-sustaining grazing, meaning they won't naturally stay in one place and destroy it but will move themselves around like elk.”
Genes Make the Bison Unique
Genetics was a major factor in deciding to take on a bison herd.
“When bison almost went extinct, some people bred them with cattle,” explains Kelly. “Now almost all bison have cattle DNA in them. We have worked to breed the cattle out of this herd over time.”
Managed by our partners at Ranchlands to achieve conservation goals, the herd is gathered once a year to undergo monitoring and DNA testing. Each animal gets an invisible microchip when they are first encountered, usually as calves, and their tail hair follicles are sent to Texas A&M University for genetic testing. Females pass on the mitochondrial DNA from cattle, so by reducing the percentage of females in the herd with cattle DNA over time, the entire herd contains less and less cattle DNA. The last two tests of our herd found only 2-3 remaining animals with mitochondrial DNA from cattle.
“It would be better if we didn’t have cattle genes in bison. The mitochondrial DNA from cattle can impact bison physiology, especially for females when breeding,” says Chris Pague.
In an unexpected and remarkable innovation, our partners at Ranchlands learned the best way to gather the bison. It used to take days to bring in the animals on horseback, but a few years ago Ranchlands started using a helicopter and dirt bikes. This proved to be a more humane method or herding, as the bison walk instead of run from the helicopter above them as they move across the ranch to the handling facility.
Bison from our herd have been utilized as a source herd for conservation efforts around the country. From the round-up each year, we sell or donate enough animals to keep the herd at a sustainable size for the ranch.
Each year, TNC's partners at Ranchlands use helicopters, dirt bikes and more to round up the bison to safely and humanely collect data about the herd for genetic research. Click on the photos to enlarge.
A Lasting Legacy
With this project, we’ve demonstrated that bison are a good fit in the San Luis Valley. TNC helped build the evidence that bison are naturally occurring in the area, and that they likely contribute ecological value to the landscape. Due to our efforts, the National Park Service is now considering plans to bring a small bison herd into Great Sand Dunes National Park and Preserve.
“At one point the whole western U.S. was covered in bison, but now all we have are little pockets of bison in different areas,” says Dewane Mosher, biologist for the National Park Service. “[At the Great Sand Dunes], we’re looking to be a satellite population for some of these other herds to preserve genetics just in case something happened to the other herds.”
Incorporating bison into the long-term vision for the park was directly influenced by The Nature Conservancy. The bison at the national park will be part of a meta population managed by the Department of Interior, meaning they can exchange genetics with other conservation herds at Yellowstone and Wind Cave national parks.
Bison at the park will support ecological outcomes and provide opportunities for visitors to observe the landscape and wildlife as they may have looked thousands of years ago.
“Our ultimate goal is good landscape condition,” says Fred Bunch, Chief of Resources Management at Great Sand Dunes. Bunch agreed that bison can be a part of restoring the landscape to boost plant and wildlife diversity.
For example, Bunch named the slender spiderflower (Cleome multicaulis). “It loves to be trampled. It’s unusual and very rare, and it really thrives where the bison have been,” says Bunch.
The National Park Service also consulted with agencies and twelve different Tribes in their planning processes.
“Every tribe really supported having bison [at the park],” explains Bunch. “When Tribes come visit the park and they see the bison on the landscape, they really appreciate that. The Tribal endorsement of bison on the landscape helped influence our decision."
Having bison at the park will ensure that these animals are part of the future for this landscape, and that visitors can see and appreciate them for years to come.
Future Outlook for Bison Conservation
In the 20 years we’ve owned a bison herd on this landscape, we’ve learned a lot of lessons. Looking ahead, we are excited to support the National Park Service in their planning and efforts to bring bison to the national park. We have also learned a lot about bison from the relatively wild state of the herd.
“Our goal was to have a bison herd that behaved like bison and interacted with that landscape in a way that they might have done historically,” says Chris Pague.
"Even in a 44,000-acre enclosure, bison are constrained. But they moved freely, created social units of their choice, and experienced reproductive selection when bulls had to aggressively compete for the ability to mate," he says.
We will continue our efforts with our bison herd to influence conservation in other places. Our research and records can contribute to bison conservation in the future. For example, we have among the longest record of bison weights over several generations of bison. By being on the ground and learning every year, we’ve made inroads in understanding how to manage these creatures and make them part of conservation outcomes for the landscape and for North America.
For now, these bison can be spotted roaming the dunes, sometimes running and usually grazing the grass under the wide-open skies of the San Luis Valley.