VISITATION OF RODENTICIDE BAIT STATIONS BY WILDLIFE SPECIES AND COMMENSAL RODENTS IN SUBURBAN ORANGE COUNTY, CALIFORNIA

Native wildlife species are frequently exposed to rodenticides used to control commensal rodent pests, especially at the urban-wildland interface. However, the exact pathways by which non-target wildlife are exposed is not clear. I used camera traps to determine the use of rodenticide bait stations by wildlife in backyards in suburban Orange County, California. I also examined local (yard) and landscape-scale variables to identify factors that might increase exposure risk for non-target species. I monitored paired bait stations with digital cameras for approximately 30 consecutive days in each of 90 yards over a six-month period from December 2017 to August 2018, and in 64 of these yards from September 2018 to April 2019. One bait station was placed on the ground, whereas another was placed 1-1.5 m to determine if elevating bait stations could reduce exposure of non-target species. Fifteen different mammal species were detected at bait stations; however, commensal roof rats (Rattus rattus) were the most common and abundant visitors, being detected at 80% of yards. Native species overwhelmingly visited ground stations, suggesting that elevating stations could reduce non-target exposure. Alternatives to rodenticides should be considered in backyards with open fencing that are close to natural areas because these types of yards tended to be visited by native wildlife. Nonetheless, given the frequency of visits to bait stations and the fact that native wildlife species were photographed entering stations, native carnivores and scavengers could potentially be exposed to rodenticides secondarily by eating native or, more likely, commensal rodent prey.