Consumption of Rat Carcasses as a Pathway of Rodenticide Exposure of Wildlife in Southern California

The high toxicity and effectiveness of anticoagulant rodenticides have led to their widespread use for controlling rodent pests; however, significant concerns remain about the potential exposure of non-target wildlife species at the urban-wildland interface. Such species can be exposed by consuming toxic baits directly, or indirectly, by scavenging rodenticide-killed prey (secondary exposure). To investigate opportunities for secondary exposure, we used Reconyx digital game cameras to quantify the fates of 20 rat carcasses placed in residential backyards in Orange County, California. We anchored rat carcasses to the ground and then followed their fates for seven days or until carcasses were removed. We also recorded yard characteristics (e.g., vegetation density, permeability of exterior barriers, presence of pets, water, and anthropogenic foods) to help explain variation in carcass removal rates between yards. Rats were discovered fairly quickly, with 35% of carcasses visited within 24 hours. Thirteen carcasses (65%) were removed within seven days, with Virginia opossums and corvids removing the most carcasses (9/13). Coyotes, free-roaming cats, striped skunks, and black rats also consumed rat carcasses, which, by the end of the trials, had attracted scavenging arthropods that then also appeared to be eaten. Yards from which carcasses were routinely removed had relatively low vegetation density; pets, water sources, and anthropogenic foods; and barrier types that permitted movement by wildlife into the yard. Our results improve our understanding of the routes by which native carnivores and scavengers are exposed to rodenticides in suburban settings and can be used to improve pest management practices