BILLINGS, Mont. - A small group of bighorn sheep has staked a claim inside a quarantined research facility for bison near Yellowstone National Park.

Workers with the Montana Department of Fish, Wildlife and Parks have tried to flush them out of the pasture a few times, but eight are still inside the pasture at Corwin Springs.

The sheep are in a double-fenced pasture separate from the one holding about 100 bison, and there's no danger of the two species mingling with one another, said Mel Frost, a spokeswoman with the state wildlife agency.

"They're not even close to the bison," she said.

But by July, wildlife officials plan on moving bison onto the pasture where the sheep are, Frost said. So between now and then, they'll have to find a way to get them it out, whether it's by hazing, trapping or being airlifted by a helicopter.

"That's our last resort," Frost said.

Meanwhile, wildlife officials are being kept busy managing bison elsewhere around Yellowstone's northern boundary.

On Tuesday, more than 50 bison captured Friday were shipped to slaughter and a bull bison was shot after it was found on private property around cattle.

The bull couldn't be hazed, and chased at least one person during the hazing operation, said Hal Harper, chief policy adviser to Gov. Brian Schweitzer. The bison got in with some horses and cows, he said, and eventually was killed.

Even though bulls are not considered to be transmitters of brucellosis, Harper said the cattle at the ranch would probably have to be tested for the disease.

Not far away, 51 bison being held at the Stephens Creek holding pen on the northern edge of Yellowstone were loaded into trailers early Tuesday. Of those, 42 were bound for meat processing plants in Idaho and nine were sent to a facility in Columbus.

The meat, heads and hides of the bison will be donated to American Indian and charity organizations.

The bison were part of a group of 193 captured Friday as part of a state and federal plan to keep the bison from wandering out of Yellowstone and into areas where they might infect cattle with brucellosis, a disease that can cause animals to miscarry.

Al Nash, a Yellowstone spokesman, said the remaining 90 bison at Stephens Creek could be shipped to slaughter in the next two days.

Park rangers on Tuesday also hazed about 40 bison just inside the northern boundary farther back into the park, Nash said.

Last month, 673 bison were captured. Of those, 583 were taken to slaughter and 87 calves were sent to the Corwin Springs quarantine facility operated by Fish, Wildlife and Parks and the federal Animal and Plant Health Inspection Service.

The quarantine will be used to help better understand brucellosis and possible vaccines.

Last summer, however, 15 bighorn sheep slipped into the upper pasture at a rocky, craggy spot where an old fence couldn't keep them out.

Since then, seven of the sheep have been pushed out of the pasture and the fence has been fortified.

State workers on foot twice tried to haze the remaining sheep out of the pasture. Both efforts, including one last week, were unsuccessful, Frost said.

"We're trying to use the least-intrusive methods possible," she said.

State officials are waiting until the bison hunt, being conducted on the northern and western edges of Yellowstone, is finished before trying other methods to move the sheep.

"We don't feel like we're in a hurry at this point. There won't be bison there until July," Frost said.