BADLANDS NATIONAL PARK, N.D. — For the first time in nearly 150 years, bison will roam a new corner of a South Dakota national park. It’s a vital step in growing the population of America’s national mammal.

Badlands National Park officials released four bison into an expanded range on Friday, Oct. 11, and if the way they careened out of their trailer onto the snow-covered plains is any indication, it seems the bison immediately made themselves at home.

The new real estate came from a land swap with a local ranch that blocked bison from entering the less rugged side of the park. Park officials worked with the U.S. Forest Service and World Wildlife Fund among others to secure the additional 22,000 acres of land in 2014, according to the National Park Foundation.

The project also included new fences along the perimeter of the new land to separate bison from local cattle.

Around 1,200 bison now live in the 244,000-acre park, and their health secures the health of their ecosystem, the foundation said. All that noshing on grassy plains creates the preferred environment for prairie dogs to set up shop, and those populations attract other animals like coyotes and birds of prey that keep the ecosystem in check.

From critically endangered to America’s national mammal

More than 30 million bison once roamed North America, but their populations plunged with Western expansion and hunting. They began to recover in the early 20th century, with the founding of the National Bison Range.

Now, there are around 31,000 of them raised solely for conservation purposes, according to the National Park Service. Another 360,000 are raised for meat and leather.

The bison finally got its due in 2016, when it was declared the national mammal of the US. President Barack Obama signed the National Bison Legacy Act, citing the animal’s historic significance in “America’s story.”