Residents of Portola Valley say they’ve been seeing a number of dead foxes and bobcats lately, leaving some to wonder if they’re being poisoned by rodenticides.
Marianne Plunder, chairwoman of the city’s Pest Control Committee, said: “We don’t know for sure if it’s the cause of the rat killing or not. “What we do know is that we have an infestation of dead wild animals. The problem is that the animals have to be found quickly before they decompose so that the cause of death can be investigated.”
He added that the city has also seen an increase in the number of mice, especially around wineries and schools. When the number of mice increases, it can be a sign of a lack of natural predators.
In the past three months, the Peninsula Humane Society has received a total of 12 reports of wildlife deaths in the Portola Valley. They all belonged to small birds, squirrels, raccoons, opossums and deer, said Director of Communications Colleen Crowley.
Dying animals of the Portola Valley
A few weeks ago, Portola Valley resident Kori-Anne Bagrowski saw a bobcat with a mange in her yard, which opens into Corte Madera Creek. He said he reported to the California Department of Fish and Wildlife and experts from the University of California, Davis. A week later, the bobcat was found dead near his property.
Some residents have reported to The Almanac that they have seen dead wildlife with other markings near Windy Hill Open Space Preserve and Westridge Road.
Mange is a skin disease caused by a parasite that causes severe itching, scabies, hair infections, starvation and dehydration in animals, according to the Tufts Wildlife Clinic.
In 2013, Midpeninsula Regional Open Space and CDFW found that many bobcat deaths and illnesses were linked to second-generation anticoagulant rodenticides, which are banned in California under the Poison-Free Wildlife Act.
Predators such as bobcats eat hundreds of rodents a year. If these prey have ingested rodenticides, the toxins can attach to the animal’s body, weakening its immune system and putting it at risk of diseases such as mange, according to Midpen.
Although some researchers have found a link between mange and anticoagulant rodenticides, the findings in many studies cannot determine for sure whether there is a direct relationship, said Ryan Bourbour, CDFW’s senior environmental scientist.
According to the 2024 CDFW Wildlife Health Laboratory Pesticide Exposure Report, 77.3% of non-game mammals, including mountain lions, bobcats, coyotes, racoons and foxes, have tested positive for exposure to one or more anticoagulant toxins.
School district rodent control efforts
Squirrels and rats have been damaging the wiring of staff cars at Corte Madera School, said Portola Valley School District Superintendent Roberta Zarea.
In January, the district began using bait boxes containing vitamin D3, which is used as a rodenticide, as recommended by the pest control company.
He added that the district only uses pesticides that are allowed under the Healthy Schools Act, which prohibits the use of certain chemicals in schools and daycare centers.
Zarea said the district notified people 72 hours before the use of rodenticides by posting signs around the campus. The demonstrations sparked public concern. As a result of the criticism, the county pulled all the trap boxes and had been using only spring traps since mid-March, “out of an abundance of caution,” Miller said.
“Our biggest concern is our students and staff,” Miller said. “Rats are a health problem when it comes to schools, so we have to prioritize (students and staff).
The county is currently exploring other ways to control rats that are less harmful to wildlife.
The Conservation Committee recommends that the first steps in pest control should be isolation and prevention. Plunder said the best pest control is an owl or a hawk, so providing nest boxes and plants for raptors is a more effective rodent control tool than poison.
In July 2025, the city began installing owl boxes, a project spearheaded by Eliza Low, a senior at the Menlo School.
How to report a dead or sick animal
Members of the public who come across a dead, sick or injured animal can contact the Peninsula Humane Society and CDFW.
If a dead animal is reported to the Peninsula Humane Society, the animal will be picked up and sometimes tested, depending on any disease outbreaks and procedures provided by CDFW, Crowley explained. The center rarely receives reports of larger mammals such as lions, deer and leopards. He said these animals should be reported to CDFW.
Contact the Peninsula Humane Society at 650-340-7022, Ext. 603.
To report dead wildlife to CDFW, use the online Wildlife Mortality Report form at wildlife.ca.gov/Conservation/Laboratories/Wildlife-Health/Monitoring/Mortality-Report. The actual form asks for information about the type, location of the body, suspected cause of death and date of death.
For questions about pesticides and regulations, or to report abuse, contact the San Mateo County Department of Agriculture.
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