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Investigation of rodenticide pathway in urban systems through isotopically labeled bait

Rodenticides, particularly anticoagulant rodenticides, are coming under increasing scrutiny in the US.  In California, several Assembly Bills have proposed the banning of, or new restrictions on, the uses of acute and anticoagulant rodenticides.  The proponents of these Assembly Bills are primarily concerned with the impacts of anticoagulant rodenticides, particularly second generation anticoagulant rodenticides, on California’s wildlife.

Studies across the US have shown varying levels of sublethal and lethal exposure of top-level predators like mountain lions, bobcats and coyotes to anticoagulant rodenticides.  In California, often over 75% of animals tested for anticoagulant residues have detections of ARs.  While little is known about the sublethal effects of rodenticides on wildlife, mortalities from rodenticide intoxication have been documented for a number of species.  

This study will investigate which species are exposed to a rodenticide in a food web with the coyote as the apex predator, after a second generation rodenticide bait is applied in bait stations to target roof rats.  A University of California Research and Extension Center site will serve as a model system in which as many individual animals as possible will be passively monitored for the presence of an isotopically-labelled bait.    The data collected from the field sites will be used to construct exposure pathways, based on the proportion of positively marked individuals of each species and the length of time the marker is detected in them.

This approach has not previously been applied to investigating rodenticide exposure pathways.  Its ability to detect evidence of consumption in many individuals through passive sampling of living animals has the potential to yield more information than other studies that have analyzed for rodenticide residues in carcasses.

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