Not so long ago, bison owned the North Dakota prairie — but over-hunting in the 1800s reduced North America’s bison population from tens of millions to fewer than a thousand.

Now a revival is underway, and a big part of that process is happening this week in the southeast corner of Theodore Roosevelt National Park.

“We’re bringing our bison in from the range to take some of the population away, which we hand off the majority to tribal recipients,” explains Blake McCann with the National Park Service.

Nearly every bison that calls the park’s South Unit home is being rounded up.

“Our primary method is helicopter,” McCann says. “We use a helicopter to go out and gauge the animals and herd them to our facility.”

It’s a slow process — if it were any faster, the bison might get spooked and run off — and it leads to the park’s low-stress handling facility. It’s an intricate maze of flags, ropes, gates, and alleyways, ultimately leading to a handling chute, where veterinarians microchip new bison and check in on repeat customers.

“We then learn something about their lifespans, their reproductive capabilities, and other details that are useful for management. The marking helps us know the individuals,” McCann says.

But the final step of this process is the most important of all.

About 175 of the park’s 500 bison are being sent down the road — donated to the Blackfeet Nation in Montana, the Standing Rock Sioux, and the Three Affiliated Tribes.

“Today we’re bringing home about 30 more, so that takes our numbers up to 100 animals,” says Cory Spotted Bear, a member of the Three Affiliated Tribes.

The round-up is a win-win: for Theodore Roosevelt National Park, it keeps the herd from disrupting the ecosystem of their home on the range.

“It helps relieve grazing pressure on public lands,” says Megan Davenport with the Intertribal Buffalo Council, “for an animal like buffalo that’s so good at surviving and thriving when it’s back out on the landscape.”

And for the Mandan, Hidatsa, and Arikara, it’s a restoration of something sacred. “To bring bison back to the people is like a resurgence of our identity and our culture,” Spotted Bear says. “Sometimes it brings tears to the elders’ eyes to see those animals released back on to what we would say are their native lands.”

That’s why the bison roundup team at Theodore Roosevelt National Park are all people you should know.

The roundup happens every two years at the park’s South Unit.