WEST YELLOWSTONE, Mont. -- The Montana Livestock Department has arrested two people and dismantled an aerial perch activists have been using in their protest of plans for a pen to capture bison just outside Yellowstone National Park.

The Livestock Department signed a Forest Service permit this week to build and operate a bison trap in the Horse Butte area for the next 10 winters.Gallatin County Sheriff's Capt. Dan Houghton said the arrests came as state officials wanted to begin work. The Montana Legislature has been debating the state's bison management plan and potential changes to it.

Members of the Buffalo Field Campaign have been occupying a platform suspended beneath a 25-foot tripod on a road leading to the trap site since late January.

The trap is meant to catch bison so they can be tested for the disease brucellosis, which causes cows to abort their calves and could subject ranchers to an expensive testing regime if their stock becomes infected.

Summer Nelson, 22, of Missoula was on a tripod Thursday as heavy machinery plowed the road to the pen site. Deputies used a knife to cut the parachute cord that bound her hands to the structure and arrested her on charges of obstructing a peace officer and resisting arrest, Houghton said.

Donald Fontenot, 35, of Portland, Ore., also was arrested when he tried to climb onto another platform.

The protesters vowed to continue opposing the trap.