FILE - In this May 8, 2003, file photo, a northern spotted owl sits on a tree branch in the Deschutes National Forest near Camp Sherman, Ore. A federal appeals court in San Francisco has upheld a plan by wildlife officials to kill one type of owl to study its effect on another type of owl. (AP Photo/Don Ryan, File)
FILE - In this May 8, 2003, file photo, a Northern Spotted Owl flies after an elusive mouse jumping off the end of a stick in the Deschutes National Forest near Camp Sherman, Ore. A new study said rat poison from pot farms in California forests appears to be poisoning endangered Northern spotted owls. Scientists for the University of California at Davis and the California Academy of Sciences published the study Thursday, Jan. 11, 2018, in the journal Avian Conservation and Ecology. (AP Photo/Don Ryan, File)
SAN FRANCISCO — Rat poison is contaminating threatened northern spotted owls in California forests, and marijuana farms appear to be to blame, according to a study published Thursday.