|
Getting your Trinity Audio player ready...
|
Portola Valley residents say they’re seeing a concerning number of dead foxes and bobcats lately, leaving some to wonder if they’re being poisoned by rodent-control chemicals.
“We don’t know for sure if rodenticide is the cause,” said Marianne Plunder, chair of the town’s Conservation Committee. “What we do know is that we have an uptick in dead wildlife. The problem is the animals have to be found quickly before they decompose to be tested for the cause of death.”
She added that the town has also seen an increase in rodent populations, especially around wineries and schools. When rodent populations swell, it can be a sign of a lack of natural predators.
Over the last three months, the Peninsula Humane Society has received a total of 12 reports of dead wildlife in Portola Valley. They were all for small birds, squirrels, raccoons, opossums and deer, said Communications Manager Colleen Crowley.
Dying fauna of Portola Valley
A few weeks ago, Portola Valley resident Kori-Anne Bagrowski spotted a bobcat with mange in her backyard, which opens up to Corte Madera Creek. She said she reported it to the California Department of Fish and Wildlife and experts from the University of California, Davis. Within a week, the bobcat was found dead near her property.
Other residents have reported to The Almanac that they have seen dead wildlife with signs of mange near Windy Hill Open Space Preserve and Westridge Road.
Mange is a skin disease caused by parasitic mites that causes severe itching, scabs, hair loss infection, starvation and dehydration in animals, according to Tufts Wildlife Clinic.
In 2013, Midpeninsula Regional Open Space and CDFW found that many bobcat deaths and illnesses were linked to second-generation anticoagulant rodenticide, which are banned in California under the Poison-Free Wildlife Act.
Predators like bobcats feed on hundreds of rodents a year. If these prey have consumed rodenticides, the toxins can build up in the predator’s body, weaken their immune system and put them at risk to diseases like mange, according to Midpen.
While some researchers have found a correlation between mange and anticoagulant rodenticides, findings across multiple studies cannot conclusively determine whether there is a direct link, said Ryan Bourbour, CDFW senior environmental scientist.
According to the 2024 CDFW Wildlife Health Laboratory Pesticide Exposure Report, 77.3% of non-game mammals, which include mountain lions, bobcats, coyotes, racoons and foxes, had tested positive for exposure to one or more anticoagulant rat poison.
School district’s rodent control efforts
Ground squirrels and rats have been damaging the wiring in staff members’ cars at Corte Madera School, said Portola Valley School District Superintendent Roberta Zarea.
In January, the district began using bait boxes containing vitamin D3, used as a rodenticide, as recommended by a pest control company.The district even alerted the town’s Conservation Committee, which did not have any concerns, said Jeff Miller, the district’s facilities and maintenance coordinator.
He added that the district only uses pesticides that are allowed under the Healthy Schools Act, which prohibits the use of certain chemicals at schools and child care centers.
Zarea said the district notified people 72 hours before the application of the rodenticides by posting signs around the campus. The signs sparked community concerns. Due to the criticism, the district has pulled all bait boxes and was only using spring traps as of mid-March, “out of an abundance of caution,” Miller said.
“Our primary concern is our students and staff,” Miller said. “Rats do pose a health issue when it comes to schools so we do have to put (students and staff) first. But of course, we’re going to follow the law and we are always going to monitor.”
The district is currently exploring alternatives to rodent control that are less harmful to wildlife.
The Conservation Committee recommends the first steps in controlling pests should be exclusion and deterrence. Plunder said the best pest control is an owl or a hawk, so providing nest boxes and vegetation for raptors is a far more effective tool for rodent control than poison.
In July 2025, the town began installing barn owl boxes, a project spearheaded by Eliza Low, a senior at Menlo School.
How to report a dead or sick animal
Community members who come across a dead, sick or injured animal can contact both the Peninsula Humane Society and CDFW.
If a dead animal is reported to Peninsula Humane Society, the animal will be picked up and sometimes tested, depending on any disease outbreaks and protocols provided by CDFW, Crowley explained. The agency does not typically accept reports of larger mammals like lions, deer and adult coyotes. These animals should be reported to CDFW, she said.
Contact Peninsula Humane Society at 650-340-7022, Ext. 603.
To report dead wildlife to CDFW, use the Wildlife Mortality Reporting system online at wildlife.ca.gov/Conservation/Laboratories/Wildlife-Health/Monitoring/Mortality-Report. The virtual form asks for details about the species, location of body, suspected cause of death and morality date.
For questions about pesticides and regulations, or to report misuse, contact the San Mateo County Department of Agriculture.
