Ask the Naturalist

Will California Ban Rodenticides that Kill Predators?

June 18, 2019

What is the California Ecosystems Protection Act (AB 1788), and what happens now that it has passed the Assembly?

Assembly Bill 1788 would ban the use of the most toxic rat poisons in California, making California the first state to do so. At the heart of the bill is the use of anticoagulant rodenticides (ARs), blood thinners that cause hemorrhaging and internal bleeding that lead to a slow death. They have been showing up in, and having disastrous effects upon, an alarmingly large swath of “non-target” species like bobcats, owls, hawks, and mountain lions.

It’s not news that ARs get into food webs. For years, ecologists have known that ARs cause major issues when non-target animals eat poisoned prey, resulting in compromised immune systems in bobcats, and the deaths of numerous hawks, owls, and apex predators like mountain lions. One study found that 90 percent of owl pellets sampled contained detectable levels of AR residue. It’s also well known that tens of thousands of children, dogs, and cats are sickened or killed every year through accidental ingestion of rat poison. What’s relatively new information, however, are the findings from a 2019 study that analyzed AR exposure research from around the world. It revealed that ARs are being found in animals like fish, insects, sea urchins, sea birds, crabs, mollusks, mallard ducks, rock doves, and more. Clearly, these poisons have a footprint in our ecosystems far larger than the bait traps they’re initially set out in.

AR history dates back to around 1950, when a handful of chemicals such as warfarin, diphacinone, chlorophacinone, and coumatetralyl were being used for rat and mouse control. Now referred to as first generation ARs (FGARs), a rodent had to make multiple meals out of these compounds before they died. Eventually, the pest control industry began to claim that rodents were resistant to FGARs and the market responded with ARs that were 100 times more potent. Now referred to as second-generation ARs (SGARs), these rodenticides only need to be ingested once to bring on death in a small mammal. It’s worth noting that in 2014, a study was published about rodents’ emerging resistance to SGARs.

Introduced by Assembly Member Richard Bloom, the California Ecosystems Protection Act (AB 1788) was voted upon for the first time on March 26, 2019 and passed from the Assembly to the Senate on May 6, 2019. Now the bill must pass through two committees in the Senate, be voted on by the full Senate, and then be considered by Governor Newsom.

If it becomes law, AB 1788 would prohibit the use of SGARs in California and also prohibit the use of FGARs on state-owned property. However, there are exemptions for agricultural use and public health emergencies. The bill sponsors, Raptors Are The Solution, Animal Legal Defense Fund, and Center for Biological Diversity realized, after previous legislative efforts had failed, that these exemptions would have to be made or the bill would never pass. “Previous bills attempted to ban all rat poisons, not just anticoagulants, but there was major pushback from chambers of commerce, business associations, apartment owners’ associations, the pharmaceutical industry, agriculture, and the poison manufacturers and the pest control operators, especially the Pest Control Operators of California,” says Lisa Owens-Viani of Raptors are the Solution, a nonprofit that advocates against rodenticide use.

The California Chamber of Commerce, California Apartment Association, and several chemical industry groups oppose the bill. They argue that rodenticides are “key tools” to preventing property damage and disease, according to a statement submitted to the California Senate Committee on Environmental Quality.

how to get rid of rats
A poster demonstrating how to get rid of rats without poison. (Courtesy Raptors Are The Solution)

This isn’t the first attempt to limit the use of ARs in order to reduce the amount of ambient poison in the environment. In fact, it’s one of a series of laws restricting the use of rodenticides in a legal long-game to protect the wildlife and ecosystems of California, and by extension, all us humans who completely rely on said wildlife and ecosystems. In 2014 California’s Department of Pesticide Regulation banned retail sales of SGARs, which laid the groundwork for the California Natural Predator Protection Act (AB 2596) in 2016, expanding on the 2014 protections by banning the use of ARs in residential and commercial areas. If passed, AB 1788 will continue to expand these protections quite a bit, greatly restricting rodenticide use by professional operators.

To stay on top of what’s happening with this bill, you can visit California Legislative Information. This website houses a fascinating trove of information regarding our state government- you can look up a bill and find its history, see how your representative has voted on it, send a comment to the author, and much more. There’s also the option to get e-mail updates on bills you want to follow, like AB 1788!

Ask the Naturalist is a reader-funded bimonthly column with the California Center for Natural History that answers your questions about the natural world of the San Francisco Bay Area. Have a question for the naturalist? Fill out our question form or email us at atn at!

About the Author

Constance Taylor is an interpretive naturalist with the California Center for Natural History. She’s a big fan of scavengers, detritivores, and decomposers because learning about their endlessly fascinating lifestyles reminds her that magic is real and nature is crazy awesome. She is especially fond of turkey vultures and flies.

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