The Ecological Benefits of Rehoming a National Park’s Booming Bison Population

In Theodore Roosevelt National Park, staffers are keeping the local ecosystem in balance by sending 300 bison to Native American tribes

Bison standing and laying in prairie grasses
Bison were nearly hunted to extinction but are now thriving in several national parks, including Theodore Roosevelt National Park in North Dakota. NPS / Jeff Zylland

In a bid to maintain a balanced ecosystem, officials at Theodore Roosevelt National Park in North Dakota will rehome roughly 300 bison with Native American tribes. The initiative aims to reduce the park’s herd from 700 to 400 individuals, reports the Associated Press’ Jack Dura.

Over the weekend, park service staffers used a helicopter to herd bison into a holding area. From there, they’ll select animals of varying ages and transfer them to several tribes: the Mandan, Hidatsa and Arikara Nation and the Standing Rock Sioux Tribe, reports Native News Online. The InterTribal Buffalo Council, a federally recognized organization that supports tribal management of bison, is facilitating the transfer.

Helicopter leading bison into holding area
Theodore Roosevelt National Park culls its two conservation herds every two to three years. NPS Photo

The bison roundup is taking place in the park’s South Unit, which is located near the town of Medora. Park service officials last reduced the size of the South Unit herd in 2021, per the Grand Forks Herald.

The park was originally established in 1947 as Theodore Roosevelt National Memorial Park—the only of its type within the broader National Park System. In November 1978, President Jimmy Carter gave the site national park status and dropped “memorial” from the name.

Though tens of millions of bison once roamed North America, the animals were hunted to the brink of extinction by the late 19th century; when the park first opened 75 years ago, no bison lived within its bounds. Thanks to concerted conservation efforts, however, their numbers have rebounded to more than half a million nationwide. That figure includes roughly 500,000 bison on commercial ranches and 30,000 in conservation herds, including two conservation herds at Theodore Roosevelt National Park.

The first bison arrived at Theodore Roosevelt National Park in 1956. A total of 29 animals were transferred to the park’s South Unit from Fort Niobrara National Wildlife Refuge in Nebraska: 5 males and 24 females. Six years later, after the South Unit herd had established itself, park service officials transferred 20 bison to the North Unit to form the second herd.

Since then, bison have thrived in the park’s prairie habitat—and the population has thrived. However, since bison have no natural predators within the park, it’s up to staffers to actively manage them. Too many bison within the park’s bounds can start to strain its limited resources, so biologists recommend keeping their numbers around 200-500 in the South Unit and 100-300 in the North Unit, according to the park. From 1962 to 2016, the park relocated 3,752 of its bison to tribes and reservations, states, zoos, other national parks and museums.

Biologist studying a bison in a chute
During the bison roundups, veterinarians perform check-ups on each individual.   NPS Photo

During the bison roundups, which take place every two to three years, veterinarians use the opportunity to assess each animal. They weigh and measure them, as well as take hair samples for genetic testing to help keep tabs on the gene pool. They also test for contagious diseases known to infect herds, such as brucellosis.

At this time, vets also attach ear tags and implant microchips into young bison that have been born since the last roundup. This allows the park to keep track of each individual bison over its lifetime.

Similar bison relocation efforts take place at other national parks, including the Grand Canyon and Yellowstone.

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