MEDORA, N.D. (AP) — A national park in North Dakota is reducing the size of its bison herd this week in a move that will benefit several Native American tribes.

A majority of the animals from Theodore Roosevelt National Park will help supplement tribal herds through the InterTribal Buffalo Council, the Bismarck Tribune reported.

"We have a constant need for animals because our tribal herds are being used, they're being utilized the way they traditionally have been, for food source, for ceremonial purposes," said Patrick Toomey, range technician for the Rapid City, S.D.-based organization

The council represents about 60 tribes across 19 states. Decisions of how to manage the herd are determined by research.

"When we manage our bison herd, we use science. Our decisions aren't made arbitrarily," said Eileen Andes, chief of interpretation and public affairs.

Wildlife biologist Blake McCann said the reduction roundup is to prevent the bison herds from getting too large to ensure there's enough available forage for the grazing animals.

He said the park aims to keep its herd at about 300 to 500 animals at the South Unit and less than 300 at the North Unit. South Dakota and North Dakota are among the states that will receive the animals.

Tooney said the Standing Rock Sioux Tribe will receive 30 to 40 bison. The Three Affiliated Tribes will be receiving five to 10 animals to establish a new bison herd in Twin Buttes.

"It's a livelihood," said Tribal Business Council member Cory Spotted Bear. "It's a symbol of bringing local opportunity back to the community of Twin Buttes."

The partnership with the park requires the animals to be kept alive for at least one year, said Toomey.

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Information from: Bismarck Tribune, http://www.bismarcktribune.com