Bison typically spend their lives peacefully munching the tall grasses that grow on America’s vast prairies. But, as humans have encroached on the large, shaggy mammals’ preferred habitat, they’ve taken it upon themselves to find new homes.
To that end, many bison, also known as American buffalo, have found sanctuary inside Grand Canyon National Park. There, they face very few of their natural predators such as wolves and mountain lions. Humans, too, mostly leave them alone, because hunting is prohibited inside the park’s bounds.
But in recent years, the number of bison living in the national park has gotten out of control. Wildlife managers say some 600 bison live within it, while there’s only capacity for around 200. Park service officials are now implementing a plan to reduce the overpopulation of bison at the Grand Canyon in the hopes of rebalancing the delicate ecosystem. Similar efforts are also underway at Yellowstone National Park, where the bison population now tops 5,000.
Earlier this month, wildlife managers relocated 58 bison from the Grand Canyon’s North Rim to nearby Native American tribes, according to a statement from the park. The park service partnered with the InterTribal Buffalo Council, which in turn helped transfer the animals to the Iowa Tribe of Oklahoma and the Cheyenne River Sioux Tribe of South Dakota.
This is just the latest bison relocation effort the park service and InterTribal Buffalo Council have undertaken together. Since 2018, wildlife officials have transferred 182 bison to eight Native American tribes across the country, per the statement. The bison management plan also includes “limited lethal removal,” per the statement, through which the park service has allowed a handful of skilled, volunteer hunters to harvest the animals. When the park service launched a lottery for volunteers last year, more than 45,000 people applied to help cull the animals, per the BBC.
Bison living at the Grand Canyon are problematic because they “damage the habitat for other species by adding to erosion, compacting soil and contaminating water sources while depleting park resources and archaeological sites,” wrote Cydney Henderson for the Arizona Republic in 2017, when park officials were still hashing out a bison management plan.
The animals first arrived in the area in the early 1900s, when entrepreneur Charles “Buffalo” Jones introduced around 100 as part of an experiment to crossbreed them with cows. His breeding plan failed, but the bison population grew and thrived. In recent years, the herd has been so successful that biologists predicted their numbers would reach 1,200 to 1,500 without any intervention by humans.
Grand Canyon buffalo have also developed some unique behaviors to adapt to their protected home. Though they can weigh between 700 and 2,000 pounds, the bison living at the park have learned to move quietly and stealthily across the landscape, likely to avoid attracting attention to themselves. This behavior has inspired a quirky nickname for them: forest ninja bison.
“They can walk through incredibly dense, dead and down wood and not make a single sound,” says Miranda Terwilliger, a Grand Canyon wildlife biologist who leads the park’s bison project, to the Arizona Daily Sun’s Sean Golightly. “They get one whiff of you and they're gone.”
The Grand Canyon bison also appear to have learned exactly where the park boundary—and their protection from most hunters—starts and ends. Bison will leave the park to get water, then make a beeline back to safety as soon as they’re done drinking. The animals also move more quickly when they’re outside the park’s bounds than when they’re inside, per the Arizona Daily Sun. Their awareness of the park’s boundary is so intriguing that park service officials are conducting research into the learned behavior.
And while the bison’s savvy adaptations have made it a bit more challenging for wildlife officials to manage the population, their ability to adapt could be cause for optimism in the face of human-caused climate change.
“The more genetic diversity you can have, the better,” Terwilliger tells the Arizona Daily Sun. “Because that means there [are] more opportunities for mutations that help with whatever the environmental challenges are.”