Bison Slowly Returning to Colorado

ROCKY MOUNTAIN ARSENAL NATIONAL WILDLIFE REFUGE — American Bison, a species that has greatly declined in number, roam on an open, recovering prairie, grazing on freshly-burned land, the Denver skyline in the background.

Rocky Mountain Arsenal National Wildlife Refuge is an ex-chemical and weapons manufacturing site turned refuge. Hundreds of millions of dollars have been spent to improve the condition of the land.

“This was not like this. This was an Army base,” said David Lucas, United States Fish and Wildlife Service refuge manager.

It’s taken years for the refuge to return to a healthy prairie environment. A large part of restoring the grasses and other plants has been the reintroduction of native wildlife.

“They’re doing great things for us,” Lucas said. “The natural systems will do a better job than we can.”

Around 180 bison roam the land now, along with hundreds of deer, prairie dogs, and coyotes, Lucas said.


Bison are a staple of the American west, including Colorado. The Arsenal isn’t the only group attempting to raise their dwindling numbers.


At Zapata Ranch, 200 miles south of the refuge, bison are being corralled into a maze-like system of pens to be tagged, vaccinated, and sorted. Here, a father and son team, Duke Phillips III and Duke Phillips IV, are working to bring back the migratory cycle of the bison and the native grasses and ecosystem. This helps keep the land more natural, reducing overgrazing because the bison move around the large swath of land instead of staying in pens until they destroy sections of the land square by square.

“They have to be managed,” said Duke Phillips IV, a co-owner of the ranch.

“Bison go where they want to go,” said Duke Phillips III, his father, the second owner of the ranch.

Herding hundreds of bison into one small area requires immense man power. The ranch used to use around 100 horses to round them up like cowboys. But now they employ more modern methods. They use a helicopter, trucks, and motorcycles. “If you know what you’re doing, they’re just walking,” Phillips III said.


Rocky Mountain Arsenal also rounds up their bison to take measurements to help them understand how their herd is recovering.


When the Rocky Mountain Arsenal National Wildlife Refuge rounds up their bison, they use trucks for a very low stress way of gently guiding the animals. They keep their bison in multiple herds so that they’re able to shift the bison based on genetics.

Bison’s genetic mingling with cattle has become an issue in the conservation of the species. There are almost no cattle genes in their bison population, but “we don’t like the word pure,” Lucas said.


Ranchers have been breeding cattle and bison together to produce bison that are more easily domesticable. This has been a problem for those trying to bring the native bison back to their old numbers and old behaviors.


The bison at Zapata Ranch are “pure” according to Phillips III. “We want a pure heard from an ideal standpoint not a functional one,” he said.

Zapata Ranch is heavily concerned with keeping the bison and their ecosystem in pristine condition.

“Ranchers have to think of themselves as environmentalists,” Phillips III said.


Even with people like the Phillips’s and Lucas, the bison are still struggling and getting minimal help from the government, besides wildlife refuges like the Arsenal which gets very little funding.


Bison aren’t on the endangered species list yet, with 20 million of them left. Their numbers seem large, but the extreme changes to their ecosystem is what’s worrying many conservationists Lucas said. The high numbers make passing legislation to protect the animals incredibly hard. The danger the bison face is real though said Lucas. “It’s a hard lift for people to comprehend.”

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