Yellowstone National Park administrators say they plan to ship as many as 600 bison to slaughter this winter if harsh conditions inside the park spur a large migration of the animals into Montana.
The Billings Gazette reports only 60 or 70 bison have crossed the park's northern boundary at last count this winter.
A state-federal agreement signed in 2000 requires the bison population to be kept at roughly 3,000 animals. There were about 4,600 as of June 2013.
Park officials say the population needs to be reduced periodically to prevent too many bison from spilling into Montana, where there is limited tolerance for them because of disease concerns.
Meat from slaughtered bison would be distributed to American Indian tribes.
Hunters have killed almost 100 bison this season.