The California Department of Fish and Game (DFG) recognizes the need for the availability of a variety of tools for vertebrate pest control and has a strong interest in ensuring that these tools are used in a way that minimizes impacts to nontarget wildlife. From 1992 to 2011, the DFG has investigated 44 cases of wildlife kills caused by vertebrate pesticides, resulting in the loss of 258 animals. While anticoagulant rodenticides were responsible for the loss of the highest number of incidents, incidents involving acute toxicants, such as strychnine and zinc phosphide, typically involved a greater number of animals per incident. Incidents of intentional poisoning of wildlife usually involved strychnine. There were no documented losses due to fumigants; however, such incidents are likely to go unnoticed because the carcasses remain underground.

In 2008, approximately 70 Canada geese were recovered dead in the Moro Cojo Slough area of Monterey County, California. Birds were necropsied and showed signs of abnormal internal bleeding. A total of 37 livers were analyzed for anticoagulants and 36 of these livers contained chlorophacinone. Death was attributable to chlorophacinone poisoning. Two turkey vultures and a barn owl also died, probably as a result of secondary chlorophacinone poisoning. The source of the chlorophacinone was not obvious, as chlorophacinone is used in several different forms on many different crops and also in commensal use. In addition, there often are several days between exposure and death, allowing the movement of the animal from the site of exposure. The ensuing investigations, which lasted several months, suggested that the exposure was due to expanded use of chlorophacinone pellets on artichokes used to control California voles. Subsequently, the label of the rodenticide product was modified to restrict its use when conditions favor goose presence in artichoke fields. No deaths have occurred since the label modification.

In 2016, the Wildlife Investigations Lab initiated a statewide mountain lion health surveillance study to understand population health and anticoagulant rodenticide (AR) exposure. Exposure to first-generation (FGARs) and second-generation (SGARs) anticoagulant rodenticides are common in predators such as raptors, wild canids (i.e., foxes and coyotes) and bobcats. However, statewide data regarding rodenticide exposure in these species, including mountain lions, have been limited. Our objectives were to determine the statewide prevalence and geographic distribution of AR exposure in necropsied mountain lions. We used liquid chromatography/mass spectroscopy to detect rodenticides in liver samples from 111 (77 male: 34 female) mountain lion carcasses from 37 counties that died between Feb 2016 and Feb 2017. Necropsied carcasses were lions taken on depredation permits, vehicular strike, public safety, or other reasons. Overall, we detected ARs from the liver tissue of mountain lions from 35 counties with 105 of the 111 (94.5%) lions having exposure. We detected FGARs in 81 individuals (73%) from 33 counties and SGARs in 102 individuals (92%) from 35 counties. Seventy-eight individuals (70%) were exposed to both SGARs and FGARs while 6 (5%) individuals had no detectable AR concentration. Of the FGARs detected, diphacinone was the most common and was observed in 67% of sampled individuals. Brodifacoum was the most common SGAR, detected in 90% of sampled individuals. Exposure to FGARs was correlated with exposure to SGARs (χ2 = 5.8, p = 0.01). Exposure to ARs was not associated with lower body condition score. Although our study represents only one year of data, we demonstrate that exposure to both FGARs and SGARs is widespread in California’s mountain lions. We recommend continued AR screening of livers from mountain lion carcasses to further enhance our understanding about the relative contributions they may have on population health. Continued monitoring would also measure the effectiveness of regulatory changes intended to reduce non-target wildlife exposure to rodenticides

Concerned that San Joaquin kit foxes from urban areas may be exposed to commensal anticoagulants, the California Department of Fish and Game, Pesticide Investigations Unit, in conjunction with the Endangered Species Recovery Program’s Urban Kit Fox Project, began monitoring San Joaquin kit foxes from the Bakersfield, CA population. Necropsies were performed and liver tissue samples collected from kit fox carcasses. Livers from archived kit foxes dating back to 1977 were also analyzed. A non-urban population of San Joaquin kit foxes from Lokern was used as a control. Other predators in the area, including coyotes and red foxes, were also analyzed for comparison. Between 1999 and 2007, tissue samples from 45 animals have been analyzed for residues of anticoagulant rodenticides. Anticoagulant compounds identified included brodifacoum, bromadiolone, pival, and chlorophacinone. Twenty-six of the 30 San Joaquin kit foxes from Bakersfield contained at least one anticoagulant, and the most commonly detected anticoagulant was brodifacoum. None of the 12 Lokern San Joaquin kit foxes contained anticoagulants. Other predators followed the same pattern: both red foxes from Bakersfield contained anticoagulant residues, but the coyote taken from Lokern did not.

Anticoagulant rodenticides (ARs) are used to control rodents around homes, buildings, and in agriculture. They have been found widely in predatory and scavenging wildlife as a result of secondary exposure and less commonly in herbivores and omnivores from primary exposure. While predators and scavengers have been monitored for AR exposure, very little information is available about AR residues in edible muscle tissue of game animals. Game animals may be exposed to ARs through direct consumption of bait, ingestion of contaminated food or vegetation, or consumption of contaminated prey items. Carcasses of three species of game animals (black bear, wild pigs, and mule deer) were collected opportunistically for this study from 2013 to 2015. Causes of death were mainly depredation, vehicular trauma, or hunter harvest. Sampling was performed in the field by California Department of Fish and Wildlife and US Department of Agriculture Wildlife Services staff. Tissues were analyzed for 37 deer in 11 counties, 120 wild pigs in 10 counties, and 12 bears in eight counties. The highest prevalence of AR exposure was found in bears, with 83% of tested livers containing ARs. Bear were most likely to be exposed to brodifacoum, a second generation AR used primarily in and around residences. Prevalence of exposure in wild pigs was 8.3%. Pigs were most likely to be exposed to chlorophacinone, used primarily in agriculture. More than half of pigs with AR residues in their liver also had AR residues in their muscle tissue. There were no AR detections in muscle samples tested for bears with AR residues in liver. None of the deer livers tested positive for ARs.

The ability to rapidly detect and respond to wildlife morbidity and mortality events is critical for reducing threats to wildlife populations. Surveillance systems that use pre-diagnostic clinical data can contribute to the early detection of wildlife morbidities caused by a multitude of threats, including disease and anthropogenic disturbances. Here, we demonstrate proof of concept for use of a wildlife disease surveillance system, the 'Wildlife Morbidity and Mortality Event Alert System', that integrates pre-diagnostic clinical data in near real-time from a network of wildlife rehabilitation organizations, for early and enhanced detection of unusual wildlife morbidity and mortality events. The system classifies clinical pre-diagnostic data into relevant clinical classifications based on a natural language processing algorithm, generating alerts when more than the expected number of cases is recorded across the rehabilitation network. We demonstrated the effectiveness and efficiency of the system in alerting to events associated with both common and emerging diseases. Tapping into this readily available unconventional general surveillance data stream offers added value to existing wildlife disease surveillance programmes through a relatively efficient, low-cost strategy for the early detection of threats.