Rodent poison harms owls

A horned owl fluffs his wings while in rehabilitation. Anza Valley Outlook/Courtesy photo

A noticeable increase in the discovery of dead owls in the Anza Valley has occurred in recent weeks. Dave Dolan said he was heartbroken to find his resident family of birds dead one morning.

“I maintain owl boxes on my property,” he said. “Barn owls are an excellent, natural way to control rodents. This morning I found my nesting pair dead below their box.”

The next day, one of the fledgling young birds was also discovered deceased. The consuming of poisoned rodents is suspected in the sudden owl deaths.

Throughout the state, poison bait used to kill rodents has inadvertently hurt or killed countless wild animals and birds of prey.

Animals that feed on squirrels, rats, mice and gophers, such as owls, hawks, raccoons, bobcats, mountain lions, foxes, skunks and coyotes, consume dead or dying rodents that have eaten these baits will also be poisoned. Dogs and cats may also eat dead or dying rodents and even bait that is within their reach.

“Please, if you are using poisons to control rodents, stop. You may have contributed in killing these beautiful birds,” Dolan said.

The use of non-chemical rodent controls, such as exclusion, trapping, encouraging natural predators and sanitation, are safer choices, he said.

The California Department of Pesticide Regulation has restricted public access to rodenticide products containing the active ingredients brodifacoum, bromadiolone, difethialone and difenacoum. These poisons may only be used by licensed professional exterminators for use in and around man-made structures. The U.S. Environmental Protection Agency has also implemented a nationwide ban on consumer use of some rodenticide products.

According to the California Department of Fish and Wildlife, they have also seen an increase in the number of strychnine-related wildlife losses in recent years. Strychnine is only legally used to control pocket gophers and must be placed underground in gopher burrows. Any above-ground use of this chemical may lead to unintentional poisoning of wildlife and pets and may lead to enforcement action by CDFW, the county agricultural commissioner or both.

“There should be some awareness before people put owl boxes up on their property. Something like checking with their closest neighbors and asking if they use rodent bait. If the answer is yes, they shouldn’t put up an owl nesting box. Of course, it won’t stop the deaths, but it may reduce the amount of nests getting poisoned,” local raptor expert Dominique Rauton said.

The anticoagulant chemicals used in rodenticide products can be transferred to an animal eating the dead or dying pest. Predators and scavengers such as owls are exposed when they eat rodents that have been poisoned with these baits.

Rodents are important food sources for many local predators, especially owls. One barn owl family may consume 1,300 mice and rats in a year.

Diane Sieker can be reached by email at