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Anticoagulant rodenticides in Strix owls indicate widespread exposure in west coast forests

September 17, 2019

Exposure of nontarget wildlife to anticoagulant rodenticides (AR) is a global conservation concern typically centered around urban or agricultural areas. Recently, however, the illegal use of ARs in remote forests of California, USA, has exposed sensitive predators, including the federally threatened northern spotted owl (Strix occidentalis caurina). We used congeneric barred owls (S. varia) as a sentinel species to investigate whether ARs pose a threat to spotted owls and other old-forest wildlife in northern regions of the Pacific Northwest. We analyzed the liver tissue from 40 barred owls collected in Oregon and Washington and confirmed exposure to ≥1 AR compounds in 48% of the owls examined. Brodifacoum, an extremely toxic second-generation AR, was the most common compound detected (89% of positive cases), followed by bromadiolone (11%), difethialone (11%), and warfarin (5%). Brodifacoum was also detected in one barred owl and one spotted owl opportunistically found dead (liver concentrations were 0.091 and 0.049 µg/g, respectively). We found no evidence that exposure varied with proximity to developed and agricultural areas, or among different study areas, age-classes, and sexes. Rather, exposure was ubiquitous, and the rates we observed in our study (38 – 64%) were similar to or greater than that reported previously for barred owls in California (40%). Together these studies indicate widespread contamination in forested landscapes used by spotted owls and other wildlife of conservation concern. Owls collected in older forests may have been exposed via illegal use of ARs, highlighting a mounting challenge for land managers and policy makers.

Publication Year 2019
Title Anticoagulant rodenticides in Strix owls indicate widespread exposure in west coast forests
DOI 10.1016/j.biocon.2019.108238
Authors David Wiens, Krista E. Dilione, Collin A. Eagles-Smith, Garth Herring, Damon B. Lesmeister, Mourad W. Gabriel, Greta Wengert, David C. Simon
Publication Type Article
Publication Subtype Journal Article
Series Title Biological Conservation
Index ID 70205387
Record Source USGS Publications Warehouse
USGS Organization Forest and Rangeland Ecosystem Science Center