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Dickson, Ariana

Prevalence of Anticoagulant Rodenticides in Ferruginous Hawk Nestlings and Evaluation of a Novel Method to Rapidly Assess Exposure

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Ariana Dickson with Ferruginous Hawk Nestling in SE Wyoming
Ariana Dickson with Ferruginous Hawk Nestling in SE Wyoming

Anticoagulant rodenticides (ARs) are compounds commonly used to control rodent pests by inhibiting an enzyme critical for synthesis of clotting factors in their blood. Secondary and tertiary poisoning of non-target species frequently occur, especially of predators that consume rodents, including many species of raptors. Although raptor exposure to ARs has been documented on at least three continents, patterns, pathways and the sub-lethal effects of exposure are not well studied. This has created a substantial need to monitor the effects of ARs in free-living populations. I evaluated the prevalence of secondary, non-target exposure to anticoagulant rodenticides experienced by a predatory raptor, and I tested the performance and suitability of technology originally developed for human patients taking oral anticoagulant drugs as a novel way to rapidly assay for AR exposure in free-living raptors.

To assess the risk of ARs to birds of prey in the western United States, I surveyed ferruginous hawk nestlings (Buteo regalis) in Idaho, Wyoming and Colorado. These hawks inhabit shrub steppes, grasslands, and deserts, many of which are modified by agriculture, wind power, and oil and gas development. Rodenticides are often deployed in or near developed areas to reduce numbers of burrowing mammals. Targeted species include ground squirrels (Urocitellus spp.) and prairie dogs (Cynomys spp.), which often compose a large proportion of ferruginous hawk diet. I evaluated the prevalence and concentrations of eight different ARs from 173 blood samples from ferruginous hawk nestlings at 60 nest sites in 2018 and 2019. I also collected 117 citrated plasma samples and analyzed them for biomarkers of AR exposure and indicators of sample quality: prothrombin time (PT), thrombin time (TCT), and fibrinogen concentration. To elucidate possible exposure pathways, I collected and analyzed 54 liver samples from hawk prey and four livers from opportunistically collected dead hawks. There were no ARs detected in any hawk blood or livers, but brodifacoum was present in one rodent liver at a minute concentration (0.003 ppm). Prothrombin time (PT) of 117 hawk nestlings averaged 29.8 ± 4.8 (SD) seconds (range: 21.3 – 41.2 sec). Sex was a strong predictor of PT, with female nestlings exhibiting longer PT. These findings aid in understanding the risk of AR exposure of ferruginous hawk nestlings in Idaho, Wyoming and Colorado and contribute important baseline information on PT of wild birds.

I also evaluated the potential of a point-of-care device, the Coag-Sense® PT/INR Monitoring System manufactured by CoaguSense Inc. (Fremont, California), to rapidly detect AR exposure in living birds of prey. The Coag-Sense® device delivered repeatable (i.e., precise) PT measurements on avian blood samples collected from four species of migrating raptors (Intraclass Correlation Coefficient > 0.9). However, PT measurements reported by the Coag-Sense system from 81 ferruginous hawk (Buteo regalis) nestlings were not correlated (r = -0.017) to those measured by standardized laboratory techniques (i.e., the accuracy of the Coag-Sense® was low). The Coag-Sense® device therefore did not accurately measure PT in this species of bird and is unlikely to do so in other birds of prey, perhaps because it uses mammalian rather than avian thromboplastin as an activator of clotting. However, this device has potential use on non-human mammals.

The Bureau of Land Management produced a great video portraying a raptor banding and identification trip in which Ariana is studying the health of ferruginous hawks at the Morley Nelson Snake River Birds of Prey National Conservation Area in southwestern Idaho with the help of volunteer naturalists.

Watch the video now!

Latest Update on Ariana:

After completing her Raptor Biology graduate program in the summer of 2020, Ariana began Veterinary School that fall at Colorado State University in Fort Collins, Colorado. She hopes to continue working on topics concerning wildlife health, especially in the realm of either toxicology or zoonotic disease research.