GARDINER, Mont. (AP) -- Nearly half the bison that left the northern edge of Yellowstone National Park in recent days were sent to slaughter Tuesday, and a park spokeswoman said more captures were likely.

About 40 bison were nearing the park boundary Tuesday and could be captured, though officials were expected to try to haze the animals back into the park, Marsha Karle said.

On Monday, as many as 110 bison were captured after leaving the park, and about 47 of them were sent to slaughter on Tuesday, she said. Protesters were in the area but not allowed near the pens where the bison were being kept, Karle said.

"We're working out the kinks of an operation we haven't used since '96-97," she said. "But everything seemed to go well."

According to a release from the Buffalo Field Campaign, "trailers with heavy police escort moved the buffalo through Gardiner this morning on their way to the slaughterhouses."

The campaign is a protest movement devoted to preventing the hazing and slaughter of bison along the stateline.

"The Lamar Valley herd was almost completely wiped out back in 1997 and now these bison are being killed off again inside Yellowstone National Park without even being tested, "said Mike Mease, a Buffalo Field Campaign representative.

Monday's capture of the wandering bison was the first on the north end of the park since the winter of 1996-97. That winter, 1,084 bison were killed. In recent years, hazing and captures have occurred more regularly on the park's west side, near West Yellowstone.

A joint management plan between agencies including the National Park Service and the state of Montana allows bison that cannot be herded back into Yellowstone to be slaughtered under certain circumstances to protect Montana cattle herds from the disease brucellosis.

Brucellosis, which infects many of Yellowstone's buffalo, can cause domestic cattle to abort and cause undulant fever in humans. Montana does not want brucellosis-infected bison on cattle grazing land that borders the park.

Under the management plan, officials attempt to haze bison that leave Yellowstone back into the park's borders. Those that cannot be moved back usually are captured and tested for brucellosis. Bison that test positive are slaughtered.

Officials said this week that the plan allows them to send animals to slaughter without first testing them if the bison numbers rise above 3,000. Park officials estimated the herd at about 3,800 earlier this winter.