A UC Davis study blames endangered owl deaths on unpermitted cannabis growing operations, and predicts the trend will escalate as the recreational weed market takes off in California.

Researchers looked at owl deaths in Humbolt, Mendocino and Del Norte counties, finding that 70 percent of northern spotted owls and 40 percent of barred owls tested positive for rat poison, believed to derive from the activities of illegal pot farming in forest clearings where they feed.

The study’s authors blame Proposition 64, the measure that legalized recreational cannabis in California.

“With its arrival, resource managers expect the number and size of unpermitted, private cultivation sites to grow, which could exacerbate the problem,” said Kat Kerlin in an article on the UC Davis website.

Scientists fear thousands of unpermitted grows will take their toll on the forest habitat and the creatures who depend on it.

The California Department of Food and Agriculture, the agency tasked with permitting growers, did not immediately respond Thursday to questions about the state’s ability to regulate cannabis farming and resources to crack down on un-permitted, potentially harmful activities.