Prevalence of Anticoagulant Rodenticides in Ferruginous Hawk Nestlings and Evaluation
of a Novel Method to Rapidly Assess Exposure
Authors: Dickson Ariana Joyce 
Published: September 2020

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.