PRAY, Mont. (AP) -- Federal and Montana agencies hit an impasse Thursday on what to do with bison leaving Yellowstone National Park -- even as biologists predicted this winter's migration could top 1,000 animals.
Park officials on Thursday offered a proposal to kill or remove up to 360 bison that enter Montana to keep the population in check and help prevent disease transmissions to cattle.
But Gov. Brian Schweitzer said he will block the shipment of any of those animals to slaughter -- as he did last year -- because of concerns such actions could spread the brucellosis disease.
Schweitzer said he has gotten mixed messages from federal officials regarding whether some bison that have been moved out of the park were diseased. Until that is resolved, the Democratic governor said, "nothing changes."
"We've got to know what is and what isn't disease-free," Schweitzer said.
Even before Schweitzer's Thursday comments, a decision on the park proposal already had been delayed until mid-January. That came after Montana officials said they had not determined how widely the animals can roam outside the park.
The uncertainties leave agencies without clear direction on how to handle bison heading into what is predicted to be a cold, wet winter. If the forecast bears out, it could trigger a large migration of bison seeking to graze at lower elevations in Montana.
Despite the impasse, Yellowstone Superintendent Dan Wenk said he remains hopeful an agreement can be reached before the migration begins. He said that will depend on how quickly the state and park can work out their differences and how soon bison start to move across Yellowstone's border.
"Maybe the stars will align," Wenk said. "We believe the things we put on the table can be effective tools to manage the bison population and reduce the risk" of disease transmissions.
The park's proposal comes after government agencies and hunters killed or removed more than 3,600 bison over the last decade under a federal-state agreement intended to prevent brucellosis transmission to cattle.
The disease causes pregnant animals to miscarry. Largely eradicated across the U.S., brucellosis persists in Yellowstone-area wildlife including elk and bison.
Federal sanctions against states that have infected livestock have eased in recent years, paving the way for changes in how bison are managed.
Allowing bison into Montana's 75,000-acre Gardiner Basin, just north of Yellowstone, is considered key to the park's proposal to more closely manage the animals through hunting. Yellowstone officials also want to ship some diseased bison to slaughter to reduce the prevalence of brucellosis among the park's two herds.
But at a Thursday meeting of state and federal officials in Pray, some wildlife advocates urged the park to back off aspects of its plans for an iconic species that one advocate referred to as "ecologically extinct." Tens of millions of bison once roamed North America. Yellowstone's two herds of the animals are considered among the most genetically pure of about 20,000 bison remaining in the wild.
"Before you harvest them, give them something back first. Let them recover," said Stephany Seay with the Buffalo Field Campaign.
Schweitzer recently suggested the park would have to "attach balloons to the bison and float them out" if it wanted to ship animals to slaughter without the state's consent.
And he insisted the only way the population control plan can work would be to include hunting inside the park, to account for those mild winters when few of the animals enter Montana.
Yellowstone administrators stiffly opposed the prospect of hunting within the park and said it would require a change in federal law.
"Even if Congress were to approve that, it would likely not be well received by the American public," said park biologist P.J. White. "Certainly the Park Service will oppose that."
Copyright 2011 The Associated Press.