Portola Valley to experiment with nonpoisonous ways to control rodents

Portola Valley, not unlike other residential communities, has problems with rodents at home with rats and mice, and on playing fields with moles, voles, gophers and ground squirrels whose collective hole-digging ways make conditions hazardous for running athletes.

Methods of controlling rodents go back a long, long way. Today, the tools for both homeowners and professional pest control agents include mechanical traps and poisons. The most effective poisons are regulated by federal and state governments and available only to the pros, but they also present danger to animals that eat the dead or dying rodents.

In the interest of protecting these predators, such as raptors and wild felines, and scavengers, such as crows and coyotes, the Portola Valley Town Council has approved a set of recommendations.

The council on March 22 unanimously agreed to a request by the town’s Conservation Committee that the town ask local businesses to end the sale of rodent poisons, urge residents and local businesses to use integrated pest management techniques, and use those techniques on town property to set an example.

Integrated pest management for rodents, according to the Centers for Disease Control, includes reducing opportunities for their access to food, water and shelter. To enter a structure, a rat needs a hole the diameter of a quarter, the CDC says. A mouse can pass through a hole the size of a dime.

Unintended results

A council staff report cites a 2013 analysis by an environmental scientist working for the California Department of Pesticide Regulation who found high percentages of poison present in predators:

• Poisons were present in an average of 79 percent of a population of 194 birds, including barn owls, great horned owls, Cooper’s hawks, red-tailed, red-shouldered hawks and golden eagles.

• Poisons were present in an average of 87 percent in a population of 237 predatory mammals, including bobcats, coyotes, mountain lions and foxes.

In these populations, rodent poisons were likely a cause of death or the cause of death for about 16 percent (or 33) of the animals, the analysis said.

A 2016 bill in the state Assembly would have banned rodenticides for all but agricultural uses, but it was opposed by the pest control industry and never made it to the floor, the staff report says.

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