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UC Davis Research Suggests Poisoning of Owls In Illegal Marijuana Farms

J. Mark Higley / Hoopa Tribal Forestry

Northern spotted owl.

J. Mark Higley / Hoopa Tribal Forestry

Many illegal marijuana grows in Northern California use rat poison to protect their crops, but new UC Davis research suggests that owls hunting in them are testing positive for rodenticides.

UC Davis researcher Mourad Gabriel says 70 percent of the spotted owls and 40 percent of barred owls were positive for anticoagulant rodenticides. The study was published Thursday in the journal Avian Conservation and Ecology. He says this was the first published account of rat poison exposure for the owls in remote forest settings.

“There could be animals out there that consume the poisoned prey and essentially hemorrhage to death internally,” Gabriel says.

He says this is the first published account for rodenticide exposure for both spotted owls and barred owls in remote forest settings. He says the data suggested there was a widespread environmental contamination uniform throughout the study area.

“Because owls are rodent-dominated predators, this now signifies the food web is contaminated,” Gabriel said.

He says there are up to 15,000 private marijuana cultivation sites in Humboldt, but the county has only permitted a fraction of them. That’s why he says there needs to be quick policy decisions are needed.

The area studied includes Humboldt, Del Norte and Mendocino counties where cannabis cultivation overlap where owls hunt. Gabriel says exposure may not be limited to owls and that other animals — like bobcats, fishers and mountains lions — that hunt the same prey are at risk of poisoning. Exposure can make the animals weaker, impact offspring and even result in death.

He added that the issue is expected to get worse with legalized recreational pot use in the state, unless conservation measures are taken up.

“When you have over 80 percent of sites that are not willing to come into environmental compliance it begs the question of is there sufficient documentation, enforcement and oversight of these private land cultivation sights,” says Gabriel.

All the spotted owls collected were found dead in forest land and were not near any urban areas, Gabriel says.

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