The controversial Yellowstone National Park bison cull is underway as park officials attempt to thin herds in an effort to maintain a sustainable number of animals. With about 4,900 bison in Yellowstone, officials plan to remove 600 to 900 animals – a number recommended by the Interagency Bison Management Plan (IBMP) partners last December, the National Parks Traveler reports.

Because bison populations continue to increase by 10 to 17% per year, annual culls are necessary to keep herds healthy and provide enough space for bison to roam, according to Yellowstone’s website. Bison are not threatened by predators like bears and wolves because of their size, leaving management of the increasing populations up to park officials. Further, while bison hunting is an option, “hunting outside of the park has not been effective….because concentrated hunting pressure along the park boundary often causes bison to return” to the park where hunting is not permitted.

Agency officials began the cull last Sunday “when bison started to move out of the park into the Gardiner Basin just to the north of Montana” and plan to continue the effort through late March, according to the National Parks Traveler. To do this, they are using three methods:

Captured bison will be held in the Stephens Creek administrative area that is closed to the public year-round. This area includes park corral operations, equipment storage, a native plant nursery and capture and quarantine facilities, according to the National Parks Traveler.

IBMP partners include the Animal and Plant Health Inspection Service, the Confederated Salish & Kootenai Tribes, the Inter Tribal Buffalo Council, Montana Department of Livestock, Montana Fish, Wildlife & Parks, the National Park Service (Yellowstone National Park), the Nez Perce Tribe and the US Forest Service (Custer-Gallatin National Forest).

In 2019, 460 bison were culled from Yellowstone.