Secondary exposure to anticoagulant rodenticides (ARs) through consumption of contaminated prey has been documented worldwide in many non-target species, especially raptors. The Red-tailed Hawk (Buteo jamaicensis), a raptor that frequents agricultural areas and eats primarily rodents, is particularly susceptible. Because there is documentation of Red-tailed Hawk exposure to ARs in California, this study aims to describe the extent to which migrating juvenile Red-tailed Hawks are exposed to ARs, as well as any sublethal effects of AR ingestion. We collected blood samples and body morphometrics from 97 juvenile Red-tailed Hawks migrating through the Marin Headlands, Marin County, CA, from August to December in 2013 and 2015, and screened samples for the presence of ARs. Eight hawks (8.2%) tested positive for some amount of ARs. We detected first-generation (diphacinone, chlorophacinone) and second-generation (brodifacoum, bromadiolone) ARs. Although some juvenile Red-tailed Hawks are exposed to ARs either along their migration route or as resident birds in the Marin Headlands, we did not find any relationship between body condition and presence of ARs. Although this method of AR sampling of live birds is novel and increases our sampling capabilities, the short half-lives of ARs in blood make it difficult to estimate population-wide exposure rates. Future studies should focus on resident raptors near agricultural areas where AR exposure can be tested over time to better understand how this technique can be used to estimate exposure rates across whole populations.
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Vol. 52 • No. 2