The Midpeninsula Regional Open Space District, also known as Midpen, learned of a problem with predator animals eating poisoned rodents after observing a mysterious outbreak of severe mange among bobcats in the Rancho San Antonio park and preserve near Cupertino. Twelve dead bobcats were found, and staff members have received numerous reports of sick and dying bobcats that are believed to have eaten rodents that ingested certain poisons known as second-generation anticoagulant rodenticides.
Family pets are also thought to have been victims of inadvertent rodenticide poisoning, some local pet owners say.
San Francisco resident Kamio Chambless thought nothing of it when she discovered her cat Bela eating a mouse, but said he suffered kidney failure afterward and eventually had to be euthanized. Chambless said her veterinarian believed rodenticide was the likeliest cause of her cat’s illness.
“I wish we’d been more aware of the possibility at the time, because we didn’t know to look out for poisoned mice,” Chambless said.
Citing hazards to pets and wildlife, state legislators have restricted the sale of certain types of rodent poison. Experts say that in addition to bobcats, the products can cause illness and death among golden eagles, coyotes and other predators when poisoned rodents enter the food chain.
The ban on anticoagulant rodenticides, set to begin July 1, prohibits the products from being sold at stores and will only make them available to state-certified pest-control professionals. But the manufacturer of one such product, d-CON, has filed suit to prevent the new restrictions from taking effect, claiming that competing products not covered by the ban may pose a greater hazard to pets.
The banned poisons, currently still available in stores, cause rodents to slowly die from internal bleeding. Researchers say the poisoned rodents can live long enough to wander into parks and wilderness areas, where they’re easy prey for predators who eat them and become sick. The state’s bobcat populations have been especially hard hit, with the animals virtually disappearing from many open-space preserves, according to experts.
There appears to be a clear link between the poisons and cases of severe mange in bobcats, according to Midpen biologist Cindy Roessler. The rodenticides can weaken bobcat immune systems until they can no longer suppress the mites that cause mange, she explained. As the bobcats become weaker, Roessler noted, they lose the ability to effectively hunt for food and die slow, painful deaths.
Midpen says it’s now rare for staff or visitors to see bobcats in Rancho San Antonio, and dead or mange-ridden animals have been reported in several other open-space preserves across 18 miles.
Ecologist Tanya Diamond said she’s seen firsthand the effects of severe mange outbreaks with a case that struck a family of coyotes near Woodside. She believes rat poison played a role because the coyotes lived next to a horse stable littered with bait stations.
The d-CON lawsuit, filed by manufacturer Reckitt Benckiser, claims the California Department of Pesticide Regulation overstepped its bounds when it adopted the ban. The company says the non-anticoagulant rodenticides that will still be legally sold in stores are potentially worse for pets, because they contain neurotoxins for which there are no antidotes. Animals poisoned with d-CON, however, can be treated with vitamin K, which is the poison’s antidote, according to a company spokesman.
But in a case where pets have been exposed to rodenticide, Daly City resident Sheila Robello recalled how veterinarians were able to save two of her pets’ lives despite there being no antidote. She said she now relies on no-bait rodent traps and doesn’t want rodenticide of any type in her home.
“There’s really no animal-safe kind of poison,” Robello said.
Midpen General Manager Steve Abbors said his organization asked the state to restrict anticoagulant rodenticides in October, but only after considering their impacts on area animals. Predators affected by the poisons play a crucial role in controlling rodent populations, and a sharp decline in bobcat numbers could lead to an overabundance of rodents in some areas, he said.