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

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.

Nest defense behaviour of four raptor species (osprey, bald eagle, ferruginous hawk, and red-tailed hawk) to a novel aerial intruder – a small rotary-winged drone

A small rotary-winged unmanned aerial vehicle (UAV) was flown above the nests of four raptor species: osprey (Pandion haliaetus), bald eagle (Haliaeetus leucocephalus), ferruginous hawk (Buteo regalis), and red-tailed hawk (B. jamaicensis) to document the parental nest defense response to the aircraft. Adult behaviour was documented with a voice recorder and an ethogram, starting ~100 m distant from the nest and continuing until the base of the nest was reached, the survey completed, and the nest area exited. All adult movements and vocalizations were recorded with distance of bird and researchers from the nest when a given behaviour occurred. Ospreys showed the strongest nest defense response followed by ferruginous hawks and red-tailed hawks with bald eagles showing the least aggressive response. Ospreys showed no greater response to the UAV in the air near the nest than to researchers simply standing at the base of the nest structure, while bald eagles showed a significantly higher response to the aircraft than researchers at the nest base. Although aggression varied, no species showed aggression at levels that would discourage the use of UAVs to survey raptor nests. When a proper flight technique is adopted, UAVs can offer a useful tool for surveying raptor nests.

Proper flight technique for using a small rotary-winged drone aircraft to safely, quickly, and accurately survey raptor nests

Small rotary-winged unmanned aerial vehicles or “drones” mounted with a small video camera were successful in surveying the nest contents of four species of raptor, including Osprey (Pandion haliaetus), Bald Eagle (Haliaeetus leucocephalus), Ferruginous Hawk (Buteo regalis), and Red-tailed Hawk (B. jamaicensis) in an accurate and safe manner when the proper flight technique was employed. A total of 110 surveys were completed in 2013 and 2014 with quality images of nest contents obtained in 106 or (96.4%) of flights. A successful and safe flight requires two personnel: the pilot who controls the aircraft and the spotter who monitors the behaviour of the adult birds defending the nest and keeps the pilot updated on all potentially dangerous interactions between aircraft and the birds. With the video camera recording, the aircraft is flown above the nest to a predetermined location that allows an unobscured camera shot of the nest. This technique can be readily adapted to a variety of habitat types and species. The accuracy of data obtained combined with the flexibility, low cost, and speed of this technique make it a useful technological alternative to the safety risks and obtrusiveness associated with traditional survey techniques.