A bison grazes after sunset in Yellowstone National Park, Wyoming, June 7, 2013.
A bison grazes after sunset in Yellowstone National Park, Wyoming, June 7, 2013.

Wildlife conservationists petitioned the Obama administration on Monday to halt the practice of killing bison from Yellowstone National Park, sometimes by the hundreds, to prevent the spread of disease to cattle that graze on neighboring land in Montana.

The legal filing by the Buffalo Field Campaign and Friends of Animals urges government agencies that manage the nation’s last wild herd of pure-bred bison to suspend the annual capture-and-culling program while undertaking a population study of the animals.

Moreover, it seeks to expand the number of bison - wooly, hump-shouldered animals also called buffalo - that are permitted to freely roam in a park that spans parts of Wyoming, Montana and Idaho.

Yellowstone biologists have determined that roughly 800 bison must be culled annually over the next several years to keep the population in check and lessen the risk that bison wandering out of the park will transmit brucellosis disease to cows.

Roughly half of Yellowstone bison are estimated to have been exposed to brucellosis, which can cause cows to miscarry.

The controversial culling program last winter saw hundreds of bison given to Native American tribes that shipped them to slaughter. Hunting of bison that migrated for food outside the park was also allowed.

An estimated 4,900 bison now roam Yellowstone, exceeding the target population of 3,000 to 3,500. The existing target established by federal and state bison managers is based on wildlife ecology as well as cultural, social and economic factors.

The culling of wayward bison has ignited a decades-long debate over management of the animals, which are a top attraction for the roughly 3 million visitors to Yellowstone each year.

The cattle industry regards the park's bison as a threat to Montana's prized brucellosis-free status, which allows ranchers to sell and ship stock across state lines without testing, vaccines or quarantines.

Yellowstone officials could not immediately be reached for comment late on Monday after the petition was filed.