Witness tells committee rodenticide exposure linked to disease, reproduction and population effects; California data shows mixed trends after moratoria

Dr. Rebecca Gulley, a postdoctoral researcher at UC Davis, told the Committee on Agriculture, Food Resiliency, & Forestry that scientific evidence ties widely used rodenticides to immune suppression, higher rates of infectious disease and reproductive harms in multiple wild species and that California’s recent moratoria show mixed early results.

Gulley testified virtually about H 326 and summarized peer‑reviewed studies and California Department of Fish and Wildlife necropsy and toxicology monitoring. She said, “82 percent [of tested eagles] tested positive for at least one anticoagulant,” while only a smaller share — about 4 percent in one national eagle survey — died from internal bleeding directly attributable to rodenticides, a pattern she described as widespread sublethal exposure.

The testimony placed those exposure data in context. Gulley cited studies associating anticoagulant exposure with severe mange in bobcats and with canine distemper in gray foxes: bobcats were reported as roughly seven times more likely to have severe mange if exposed to two anticoagulant compounds, and gray foxes were four to seven times more likely to contract and die from distemper when exposed at varying levels. She said researchers believe immune compromise from the poisons is the likely mechanism.

Gulley also described reproductive and in‑utero transfer concerns. She cited a documented case of a collared California mountain lion (known as P-54) and its four fetuses testing positive for multiple anticoagulants, and referenced smaller case reports in bobcats and domestic animals in which fetuses showed exposure. On avian reproduction, she summarized a plantation study that found higher barn‑owl nesting success where rodenticides were not used and worse reproductive outcomes in sites using second‑generation anticoagulants.

Turning to non‑anticoagulant rodenticides, Gulley highlighted growing detection of bromethalin (a neurotoxin) in raptors. She cited a Tufts University raptor‑center study finding about 30 percent of sampled red‑tailed hawks and 18.2 percent of barred owls testing positive for bromethalin, and said the clinical signs of neurotoxin exposure can overlap with trauma or avian influenza, complicating attribution.

On policy outcomes and monitoring, Gulley summarized California’s regulatory timeline and statewide monitoring. She said AB 1788 (moratorium on many second‑generation anticoagulant rodenticides) was enacted 01/01/2021 and that later legislation extended restrictions on certain first‑generation products (discussed as enacted 01/01/2024 for the compound named in testimony). She told the committee the California Department of Fish and Wildlife’s routine necropsy and toxicology program shows a gradual decline in second‑generation anticoagulant detections after AB 1788, while first‑generation anticoagulant detections showed a tentative increase in some years after that moratorium — an outcome the presenter said was a concern the state has been monitoring.

Gulley said the statewide pattern of detections appears broadly distributed across urban, agricultural and natural lands in California rather than limited to any single land‑use type. She noted the moratoria include exemptions for agricultural use and for declared public health emergencies and testified that, to date, California had not declared a public health emergency that triggered broad re‑use of anticoagulants after the moratoria.

To address local rodent management needs without the same environmental risks, Gulley described pilot work on rodent fertility control combined with improved sanitation and exclusion. “The goal here would be to almost use the rodent fertility control in replacement of the poison,” she said, summarizing field trials that use bait monitoring and camera traps to measure population declines and persistence; in closed populations some trials reported large declines within months, while open, migratory populations declined more slowly but still trended downward.

Committee members asked follow‑up questions during the session. Representative O’Brien asked whether climate or other cofactors could be involved; Gulley agreed multiple stressors (climate, population density, co‑infections) likely interact with toxicant exposure. Representative Nelson asked whether the studies predated recent federal reclassifications and about furbearer population changes after state trapping bans; Gulley said some studies predated recent regulatory shifts and that population trends vary by species, with gray foxes described as stable or declining in many states.

Gulley offered to provide the committee with specific statutory language about the public health‑emergency exemption, plus her slides and contact information; she said she would forward those materials to the committee assistant.

The testimony provided the committee with recent monitoring results, peer‑reviewed study findings and suggested non‑poison alternatives that lawmakers and staff can evaluate while clarifying the scope of exemptions and measuring public‑health implications.