Toxicological responses to sublethal anticoagulant rodenticide exposure in free-flying hawks

Authors: NIMIS, VYAS - Us Geological Survey (USGS); RATTNER, BARNETT - Us Geological Survey (USGS); LOCKHART, MICHAEL - Us Geological Survey (USGS); HULSE, CRAIG - Us Geological Survey (USGS); Rice, Clifford; KUNCIR, FRANK - Us Fish And Wildlife Service; KRITZ, KEVIN - Us Fish And Wildlife Service

Submitted to: Environmental Science and Pollution Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2022
Publication Date: 5/28/2022
Citation: Nimis, V., Rattner, B., Lockhart, M.J., Hulse, C.S., Rice, C., Kuncir, F., Kritz, K. 2022. Toxicological responses to sublethal anticoagulant rodenticide exposure in free-flying hawks. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-022-20881-z.
DOI: https://doi.org/10.1007/s11356-022-20881-z

Interpretive Summary: Raptors are threatened by many factors in prairie regions of the US and Canada and are listed as birds of concern by federal regulators. This study offered use of red tailed hawks as a surrogate for protected raptors to better understand indirect poisonings caused by baiting to control prairie dogs. Evidence for subtle effects transferred to red tailed hawks feeding on moribund prairie dogs was assembled by blood clotting measurements and subsequent behavioral observations during release and telemetry tracking. The agent studied was Rhozal that uses chlorphacinone as the active ingredient. Measured residues contained in prey that had suffered exposure were used to feed the captive birds. Seven days after feeding, reductions in blood clotting were observed when compared to reference birds feeding on clean tissues. The treated birds also showed increased feather fluffing to manage cold stress during the free range observations. This study offered clear signs of chlorophacinone poisoning in raptors in a carefully controlled prey feeding study. This information will be of use to scientists and policy makers.

Technical Abstract: We offered the Rozol-contaminated prairie dogs (Cynomys ludovicianus) to six wild-caught red-tailed hawks (Buteo jamaicensis), and uncontaminated prairie dogs to two wild-caught red-tailed hawks for 7 days. On day 6 of the exposure, blood was collected from the eight hawks to determine chlorophacinone's effects on coagulopathy. Russell's viper venom time and prothrombin time of chlorophacinone-exposed hawks exceeded the reference hawks' means by more than 5 standard deviations. Coagulopathy results also confirmed that the hawks in the treated group were being exposed via secondary poisoning to chlorophacinone. On day 7, the hawks were fitted with tail-mounted VHF radio telemetry transmitters. Red-tailed hawks were released the following day and their survival was monitored for 33 days. Four of the six chlorophacinone-exposed hawks exhibited ptiloerection, an indication of thermoregulation disfunction. No clinical or physiological overt effects were detected in the reference hawks. We postulate that frequency and duration of ptiloerection was modulated by territory and mate quality. It is noteworthy that prothrombin time values correlated with the frequency and duration of ptiloerection. This study is a first to relate coagulation times to a sublethal physiological effect in free-ranging birds.