Researchers at the University of California released a study yesterday indicating that rat poisons increasingly pose a significant risk for California’s imperiled Pacific fishers, small forest-dwelling mammals that are protected under the California Endangered Species Act. The study shows that increasing numbers of fishers are being exposed to and dying from greater varieties of rat poisons, or rodenticides, found at illegal marijuana farms. It also affirms reports and data from across the state that rodenticides continue to poison and kill numerous California wildlife species.

Poisons from illegal marijuana grow sites are killing increasing numbers of fishers in California. Here, Mourad Gabriel of the Integral Ecology Research Center stands among all the trash at a illegal marijuana grow site in Northern California. Photo credit: Mark Higley / Hoopa Valley Tribal Forestry

“These poisons are silently killing our country’s most majestic wildlife by indiscriminately causing animals to literally bleed to death from the inside out,” said Jonathan Evans, environmental health legal director at the Center for Biological Diversity. “It’s time to ban these poisons from the market to protect fishers, bald eagles, great horned owls and kit foxes from a painful, gruesome fate.”

Anticoagulant rodenticides interfere with blood clotting, resulting in uncontrollable bleeding that leads to death. These slow-acting poisons are often eaten for several days by rats and mice, causing the toxins to accumulate in their tissues and poisoning predators that eat the weakened rodents. Other types of rodenticides threatening wildlife include neurotoxins and poisons that calcify soft tissue.

“Fishers are the flagship species,” said Mourad Gabriel. “We have to think of so many species, like Sierra Nevada red foxes, spotted owls, martens—they all are potentially at risk. This is essentially going to get worse unless we do something to rectify this threat.”

Previous studies by the California Department of Fish and Wildlife have documented rodenticides in more than 75 percent of wildlife tested, including eagles, owls, bobcats, mountain lions, endangered San Joaquin kit foxes and 30 other wildlife species. Even after California took steps in July 2014 to reduce exposure from certain types of rodenticides, exposure and poisoning by rodenticides remains prolific.

The new study was led by Mourad Gabriel, formerly at the University of California Davis and now at the Integral Ecology Research Center in California. Exposure rates in fishers to rodenticides increased from 79 percent in 2012 to 85 percent in the most recent study. Necropsies of fishers confirmed as many as six different rodenticides in one animal. Some of the chemicals found were considered safer alternatives to other commercially available rodenticides, but they nonetheless killed fishers.

This fisher, brought to UC-Davis for a necropsy, was poisoned by anticoagulant rodenticide (rat poison) found on an illegal marijuana grow site in Northern California. Photo credit: UC-Davis

“Fishers are the flagship species,” said Gabriel. “We have to think of so many species, like Sierra Nevada red foxes, spotted owls, martens—they all are potentially at risk. This is essentially going to get worse unless we do something to rectify this threat.”

Safe alternatives to rat poison can be used to address rodent outbreaks in homes and rural areas. Effective measures include rodent-proofing by sealing cracks and crevices and eliminating food sources in homes, providing owl boxes to encourage natural predation on farms and utilizing traps that don’t involve these highly toxic chemicals. For more information visit SafeRodentControl.org.

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