A new study examining the presence of rodenticide in northern spotted owls has found an alarming rise in exposure to rat poison emanating from illegal marijuana farms. Writing in the journal Avian Conservation and Ecology, researchers at UC Davis, in cooperation with the California Academy of Sciences, say the boom in unpermitted and private farms near critical forest habitat is likely the driving force behind the spike.

"When you have thousands of unpermitted grows and only a handful of biologists that regulate that for multiple counties, we’re deeply concerned that there aren’t sufficient conservation protective measures in place," lead author Mourad Gabriel said in a statement. "If no one is investigating the level at which private marijuana cultivators are placing chemicals out there, the fragmented forest landscapes created by these sites can serve as source points of exposure for owls and other wildlife."

Researchers conducted their study by collecting dead specimens of northern spotted owls, a threatened species under federal and state Endangered Species acts, along with barred owl tissue samples from an unrelated project. They discovered that seven of the 10 spotted owls, and 40 percent of the barred owls, tested positive for rat poison.

"Spotted owls are inclined to feed along forest edges," added Gabriel. "Because grow sites break apart these forest landscapes, they are likely source points for exposure."

Exposure to high doses of rat poison can cause clotting and coagulation complications, leading eventually to uncontrollable internal bleeding. Even sublethal doses, as research ecologist Craig Thompson told MNN in 2016, can later result in mortal wounds.

"There's a lot of records of animals coming into wildlife rehab that end up dying from rodenticide poisoning, but it's small injuries," he said. "They'll bleed out, essentially. I read that one great horned owl bled out from a mouse that bit it on the toe."

A pair of juvenile northern spotted owls. A pair of juvenile northern spotted owls. (Photo: John P Dumbacher © 2017 California Academy of Sciences)

As you might expect, the impact of rat poisons from illegal marijuana farms also has been documented as deadly to black bears, grey foxes and other animals down the food chain. An earlier study by Gabriel, who also serves as executive director of the nonprofit Integral Ecology Research Center, found 85 percent of 101 fishers (cat-sized members of the weasel family) tested positive over a four-year period to exposure to rodenticides.

As Gabriel explains in the video below, banned chemicals, such as the notorious insecticide DDT, are also being used in illegal grow sites throughout the northwest U.S. on private, public and tribal lands.

Unfortunately for species and those tasked with ensuring their survival, the dichotomy between state and federal regulations on the sale of marijuana isn't likely to alleviate the intrusion of black-market growers into critical habitats any time soon. As California presses ahead with its commercial approach, all conservationists can hope for are the funds to pursue greater oversight and enforce laws.

"We need more staffing," Sgt. Ray Duncan of Sacramento County told The Sacramento Bee. "We just don’t have the manpower. We can’t keep up."

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Illegal pot farms are endangering spotted owls
As unpermitted grow sites and recreational marijuana use expand, researchers say the lack of regulatory oversight will only exacerbate the problem.