Conservation efforts and reintroduction of the American bison (Bison bison) in Colorado began in Denver during the early twentieth century. By that time, the bison population had declined precipitously since the mid-nineteenth century because of overhunting and the development of cities, railroads, and farms. Efforts to protect bison were rooted in the decline of Indigenous populations, the end of Colorado’s status as a “frontier” state, and a growing conservation movement that lamented the costs of urbanization and industrialization.
Since the early 1900s, tribal, state, county, and university efforts to help bison populations recover in Colorado have been largely successful. Today there are more than 100 bison across multiple managed herds in the state, and the bison population across the West numbers around 25,000. As Colorado’s conservation herds continue to grow, management processes have become more precise, and the herds are readily available for research, engagement, or viewing across the state. In 2016 President Barack Obama declared the bison the official mammal of the United States.
Bison are the largest mammal in North America and a keystone species of the shortgrass prairie ecosystem. In 1800 there were more than 30 million bison across the American West. They roamed the Colorado plains in thick herds, sustaining the prairies and the Lakota, Cheyenne, Pawnee, and other Indigenous nations.
The fur trade era dealt the first blow to the bison. In the 1830s, trading posts such as Bent’s Fort, Fort Vasquez, and others became centers of the bison robe trade, which offered Indigenous nations access to American and European cookware, weaponry, and tools. At a time when many Indigenous nations were struggling or came into conflict because of the United States’ aggressive expansion, access to these goods gave nations such as the Cheyenne and Arapaho an advantage over others. Native Americans killed many more bison than they needed for survival to maintain this advantage.
The robe trade did not last long, but things did not improve for bison. The Comanche, arguably the most powerful nation on the plains at the time, not only overhunted the animals to sustain a large raiding-and-trading empire but also built up massive horse herds that competed with the bison for grazing territory. A drought beginning in the 1840s starved many bison, and white colonists added to the pressure as they crossed the plains on wagon trails, killing thousands of the animals for food and other needs.
Steeped in the mythology of Manifest Destiny, US soldiers, miners, boosters, and politicians also came to understand that killing the bison would weaken Indigenous nations. In 1868 General William T. Sherman suggested that the federal government organize a “grand buffalo hunt” on the plains to cause harm to Indigenous nations and make way for mines, railroads, and cities. While it was never an explicit government policy, eliminating the bison proved effective. Food scarcity contributed to the forced removal of the Cheyenne, Arapaho, and other Plains peoples from Colorado in the late 1860s.
Market forces also continued to run roughshod over the bison. In the 1870s, tanners developed a more efficient method for creating bison leather, and railroad expansion allowed for easier transportation of the heavy hides. By 1873 white hunters, sometimes with ammunition from the military, were killing nearly fifty bison a day. By the time Colorado became a state in 1876, hunting and habitat destruction from farms, cities, and railroads left only a few hundred bison south of the Platte River. The northern herd suffered a similar fate in the early 1880s.
American observers began to see the significance of the bison’s decline as early as 1875, when a bill to ban bison hunting made it to President Ulysses Grant’s desk. Grant vetoed it, however, as the US Army was still fighting Indigenous nations (including those who had already been forced out of Colorado). As the nineteenth century drew to a close, the US army massacred, force-marched, and starved Native Americans off their lands, and Congress privatized reservation lands, much of which were sold off to non–Indigenous people.
With Indigenous nations severely depopulated and no longer perceived as a threat, white immigrants now lamented the loss of bison, especially as the animals became an important part of the frontier mythology portrayed by William “Buffalo Bill” Cody. While Cody’s popular Wild West Shows made the bison a symbol of a romanticized American West, sportsmen grew concerned that there would soon be no more trophies to hunt. Sentiment turned against wanton bison killing. In 1886, for example, the Denver Tribune-Republican admonished a group of bison hunters in South Park, calling for the state “to enact a law prohibiting the killing of buffaloes at any season of the year.”
Theodore Roosevelt can be counted as one of the many Americans, and perhaps the most influential, who did an about-face on bison. In the 1880s, he advocated for the bison’s disappearance to make way for American homesteading and ranching. But by his presidency in the early 1900s, he had changed his mind. He became one of the founding members of the American Bison Society, which sought to reestablish North America’s bison population. At a 1907 meeting in New York, the society reported some 2,250 bison left on the continent, with 1,400 in the United States. Later that year, the society completed the first animal reintroduction in the United States, when it moved fifteen bison from the Bronx Zoo to a wildlife refuge in Oklahoma. One year later, the group successfully persuaded Congress to create the National Bison Range on the Flathead Indian Reservation in Montana. Meanwhile, President Roosevelt’s establishment of National Forests across the country reflected this growing interest in conservation, as the environmental costs of industrialization became clearer and sportsmen wanted to preserve disappearing trophy species.
Efforts in Colorado
In 1908 eighteen bison at the Denver Zoo were all that remained of the animal in the state. In 1914 the city acquired more bison from Yellowstone National Park and moved the growing herd to a 165-acre natural enclosure at Genesee Park. In 1938 the Denver herd had again outgrown its environs, so twenty bison were moved to Daniels Park in Douglas County. These two Denver Mountain Park herds have continued to expand and still roam across hundreds of acres on the outskirts of the metro area.
Elsewhere in Colorado, small herds of bison have been reintroduced or preserved on ranches and public spaces. At Rocky Mountain Arsenal National Wildlife Refuge in Adams County, a conservation herd of sixteen bison was reintroduced in 2007 from the National Bison Range in Montana. It has since expanded to a population of more than 180 in 2020.
The 2015 reintroduction of ten bison to Soapstone Prairie Natural Area and Red Mountain Open Space in Larimer County has proven successful. Facilitated by the US Department of Agriculture, Colorado State University, Larimer County, and the City of Fort Collins, this bison herd shares genetic links to the last-surviving wild bison in Yellowstone National Park. The result of diverse scientific and agricultural research endeavors, the Laramie Foothills Herd now numbers close to eighty animals and has provided seed stock for other herds in Colorado.
The principal obstacle to the healthy reintroduction of bison to Colorado is brucellosis, the disease caused by the bacterium Brucellosis abortus. This bacterium causes the sudden death of the bison fetus in utero, threatening the viability of reintroduction efforts and the growth of wild herds. The disease, which affects a variety of domesticated and wild mammals, has nearly been eradicated, save for remnant populations of the bacterium in the Yellowstone bison and elk herds. Any bison reintroduction effort requires careful stewardship to avoid introducing the disease to new herds.
Identifying and eradicating the bacterium are together a significant part of the efforts at the Laramie Foothills Bison Conservation Herd in Larimer County. Using assisted reproductive technologies like artificial insemination, in-vitro embryo production, embryo transfers, and the careful washing of sperm and embryos, researchers ensure that the Laramie Foothills Conservation Herd is expanding safely and curtailing the spread of the disease.
Research on the Laramie Foothills herd has informed other bison preservation efforts throughout the state. In Las Animas County, a herd of ten bison was introduced with the help of Colorado State University, the Southern Plains Land Trust, and the nonprofit Defenders of Wildlife. This herd, located at the Heartland Ranch Nature Preserve, is doing well on the plains in southern Colorado.
Indigenous Conservation Efforts
In La Plata County, the Southern Ute Tribe has been carefully tending a bison herd reintroduced in the 1980s. The Southern Ute Cultural Department leads the initiative to distribute bison meat for tribal members, powwows, and tribal functions. The Cultural Department also provides opportunities for education about the bison’s central role in Southern Ute culture.
The Southern Ute Tribe is one of the sixty-nine tribes operating collectively as the InterTribal Buffalo Council (ITBC). This intertribal coalition works to preserve bison herds across nineteen US states, including Colorado. The ITBC’s efforts have been successful, as it now represents more than 2,000 heads of bison nationwide.
In 2021 the city and county of Denver gifted more than a dozen bison to the Southern Cheyenne and Southern Arapaho Tribes in Oklahoma. The tribes’ bison program serves similar functions like the one on the Southern Ute Reservation, coordinating access to bison meat as well as research and management of the herd.
Just ten minutes from downtown Denver, the Rocky Mountain Arsenal National Wildlife Refuge hosts more than 300 species of prairie life, including a bison herd. West of Golden, the Genesee Park herd can often be seen from the roadside overlook off exit 254 on Interstate 70. Halfway between the south Denver suburbs and Castle Rock, Daniels Park also features bison observation areas. In Larimer County, the Laramie Foothills Bison Conservation Herd can be seen from elevated viewing areas at Soapstone Prairie Natural Area or Red Mountain Open Space.
Opportunities to observe, research, and rely upon the American bison were nearly lost in the late nineteenth century, but preservation and reintroduction efforts have turned small remnant populations into thriving herds. As Colorado’s herds benefit from research and diverse management solutions, the population will continue to grow, creating more seed herds and solidifying the bison’s resurgence in its ancestral prairie home.