BOZEMAN (AP) -- Eight bison briefly escaped from an experimental brucellosis quarantine facility near Yellowstone National Park on Monday, but they didn't get very far.

''Three of them walked back in on their own and five were standing by the gate,'' Keith Aune, a researcher for the Montana Department of Fish, Wildlife and Parks, said Wednesday.

The bison escaped because a padlock didn't fully latch, said Aune, who speculated the wind might have rattled the gate, opening the lock.

The eight bison were free for about six hours.

The facility holds 47 bison between 1 and 2 years old. The animals were captured as calves as they left Yellowstone National Park the past two winters. They then became part of the quarantine program meant to determine whether certified disease-free bison can be sorted from the park herd.

All the animals have been tested several times, as researchers try to find the best way to test for brucellosis.

The overall goal is to eventually release brucellosis-free bison on other public or tribal lands. Some could be ready for release in the fall of 2008, if all goes as planned.

The Buffalo Field Campaign, a bison advocacy group that opposes the quarantine program, called for its immediate halt.

''Quarantine is the antithesis of buffalo restoration,'' BFC said in a press release. ''Wild buffalo restore themselves naturally, every year when members of the Yellowstone herd attempt to migrate, but the government keeps getting in the way and killing them for trying.''