Yellowstone National Park just announced plans to kill up to 900 bison this winter in an effort to control the size of the park’s herd. Any animals that stray from the park over the winter months will be killed in what could be the largest cull of the US’ last free-ranging pure-bred bison in seven years. Currently, Yellowstone‘s bison population is estimated at 4,900, and the park hopes to reduce this number to 4,000.

yellowstone bison cull

Yellowstone’s park management plan sets the target population of bison at between 3,000 and 3,500 animals. It has been determined that this is the population size the park can support over winter without supplementary feeding. It’s also considered large enough to maintain the genetic integrity of the bison population, while preserving the ecological function that the animals provide as grassland grazers and a source of food for carnivores. The culling or removal of some migratory bison was agreed upon by the park due to the risk of the bison wearing out their welcome on farmland in neighboring areas.

Related: Yellowstone National Park Rejects Plan to Shoot Bison With Vaccinated Biobullets

About half the bison population of Yellowstone carries brucellosis, thought to have been introduced to the park by cattle who used to graze there. The disease can cause miscarriages in cows and has been successfully eradicated from cattle in Montana, although there is concern that bison migrating out of the park could reintroduce the bacterial disease. However, according to Defenders of Wildlife, there has not been a single documented case of bison transmitting the disease to cattle in Montana. Given that an estimated 50 million bison used to roam the plains, this is yet another example of human-induced habitat loss infringing on the natural migratory activity of native animals.

The cull plan has been in place since 2000, and has resulted in thousands of bison being either killed in managed hunts or caught and shipped to American Indian tribes for traditional hunting and consumption. The number of bison that leave the park each year depends on the severity of the winter weather. In the mild winter of 2011-2012, fewer than 40 bison were culled after leaving the park. However, in the winter of 2007-2008 more than 1,600 bison were killed when they left the park boundaries in search of food. Wildlife advocates Friends of Animals and the Buffalo Field Campaign filed a legal petition with agencies including the National Park Service and U.S. Forest Service on Monday in an effort to stop this year’s cull. Defenders of Wildlife also have an online petition you can sign, calling on Montana Governor Steve Bullock to stop the cull.

Via The Huffington Post

Photos by Harvey Barrison and Tony Hisgett via Flickr