GRANTS PASS, Ore. — In the West Coast marijuana-growing region known as the Emerald Triangle, scientists want to know whether the rat poison spread around illegal pot plantations is killing northern spotted owls, a threatened species.
But because it is so rare to find a spotted owl dead in the forest, they will be looking at an invasive cousin owl from the East that has been pushing spotted owls out of their territory since the 1990s.
Mourad Gabriel, a doctoral candidate at the University of California, Davis Veterinary Genetics Laboratory, said Tuesday they are testing 84 barred owls from Northern California killed in the course of research on whether removing them allows spotted owls to reclaim lost territories. Those owls were collected primarily by the California Academy of Sciences and Green Diamond Resource Co., which grows redwood for timber.
Among the first roughly 10 barred owls tested, about half have been positive for the poison. Two spotted owls found dead in Mendocino County in Northern California also tested positive for the poisons, Gabriel said.
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The research is funded primarily by the U.S. Fish and Wildlife Service.
Eric Forsman, a U.S. Forest Service wildlife biologist and a leading expert on spotted owls, said he did not think the rat poisons would be a significant factor for spotted owls in northern Oregon and Washington, where their primary prey is the flying squirrel and there aren’t as many illegal pot plantations on federal lands.
Loss of old-growth forest habitat and the invasion of the barred owl remain the primary threat to the birds, whose numbers continue to decline.
The rat poison could be significant, however, in the southern part of their range — Northern California and southwestern Oregon — where they feed primarily on dusky-footed wood rats and pot plantations are abundant, Forsman said.
Spotted owls in Southern Oregon and Northern California have been declining at the rate of 5 to 15 percent a year from 1990 to 2008, the Fish and Wildlife Service said.
Scientists have already established that common household rat poisons spread around illegal pot gardens to keep rats from eating the plants have been poisoning fishers, a large cousin of the weasel that is being considered for protection by the Endangered Species Act.
One of the threats to the fishers being analyzed is the poison at the pot gardens, which are common on federal and tribal lands in Northern California and Southern Oregon.
Gabriel said researchers hoped to expand the testing of dead owls once the Fish and Wildlife Service approves a program to experimentally remove barred owls from spotted-owl territories on federal and tribal lands.