Federal authorities were investigating the attempted release of about 50 mink by members of the Animal Liberation Front from a Jefferson farm, officials said.

FBI agents spent Wednesday morning gathering evidence at the Jefferson Fur Farm, agency spokeswoman Beth Ann Steele said.

The released mink were discovered about 6 a.m. Monday, Steele said. Farmworkers caught them all before they could get away.

"Guard dogs started barking right away, and the owners woke up and were able to recover the mink," Steele said.

A press release placed online Tuesday by the Animal Liberation Front contained an apparent threat against the farm's owners. It was signed by ALF-Cascadia.

"Consider this your first warning," it read. "Tear down this death camp and let the mink live free. If you don't, we will be back to finish the job."

The ALF is considered a domestic terrorist group by the U.S. Department of Justice, and its threats are taken seriously, Steele said.

The group's press release referred to them as "masked avengers" and acknowledged that some of the freed animals likely would not survive their release.

"It will be a hard road ahead for these mink and their offspring, but with our help, they now have a chance at survival," the release read. "Even if some of the mink do not make it, we feel is it better to die free than at the hands of their speciesist captors."

The Marion County Sheriff's Office is assisting in the investigation.

The perpetrators destroyed breeding records, said Teresa Platt, the executive director of Fur Commission USA.

Platt's Coronado, Calif.-based association represents mink farmers in 28 states and keeps track of ecoterrorist incidents. Platt estimated the loss of the records was $5,000.

"Everybody in Oregon and agriculture has probably gone on alert because of this," Platt said.

rliao@StatesmanJournal.com or (503) 589-6941