High rates of anticoagulant rodenticide exposure in California Barred Owls

Pesticide use is pervasive and the exposure of non-target wildlife has been well documented over the past half century. Among pesticides, anticoagulant rodenticides (AR) have emerged as a particularly important threat in forests of the western United States, with exposure and mortality reported for several species of conservation concern. To further quantify this threat, we collected specimens of Barred Owls (Strix varia) and Barred Owl x Spotted Owl hybrids from the Klamath and Cascade Mountains and Sierra Nevada in California, USA to use as indicator species for environmental contamination with AR and to infer exposure of closely related and ecologically similar Northern and California Spotted Owls (S. occidentalis caurina, and S. o. occidentalis, respectively). We tested 115 Barred Owl and 12 Barred Owl x Spotted Owl hybrid livers for eight AR compounds and found high rates of exposure (62%) across our study area, and greater than previous studies in the Pacific Northwest. In additio...