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

An important component of assessing the hazards of anticoagulant rodenticides to non-target wildlife are observations in exposed free-ranging individuals. The objective of this study was to determine if environmentally realistic, sublethal first-generation anticoagulant rodenticide exposures via prey, can result in direct or indirect adverse effects to free-flying raptors. We offered black-tailed prairie dogs (Cynomys ludovicianus) that had fed on Rozol® Prairie Dog Bait (0.005% active ingredient chlorophacinone) to six wild-caught red-tailed hawks (RTHA, Buteo jamaicensis), and uncontaminated black-tailed prairie dogs to two wild-caught RTHAs for 7 days. On day 6, blood was collected from all eight RTHAs to determine chlorophacinone’s effects on blood clotting time. Russell’s viper venom time and prothrombin time of chlorophacinone-exposed RTHAs exceeded mean values of reference RTHAs by more than 5 standard deviations. The observed coagulopathy confirmed that the RTHAs in the treated group were exposed to and adversely affected by chlorophacinone via secondary exposure through diet. On day 7, the RTHAs were fitted with tail-mounted VHF radio telemetry transmitters. Red-tailed hawks were released the following day and their fate (survival, activity, and overt physiological condition) was monitored for 33 days. Four of these six chlorophacinone-exposed free-flying RTHAs exhibited ptiloerection, an indication of thermoregulatory dysfunction due to chlorophacinone toxicity, but no signs of intoxication were observed in the reference hawk. It is noteworthy that prothrombin time values were associated with the duration and frequency of ptiloerection. These findings demonstrate that sublethal chlorophacinone exposure can directly or indirectly evoke adverse effects in wild birds. Furthermore, our anecdotal observations suggest that duration and frequency of ptiloerection from low level CPN exposures may be modulated by territoriality and mate presence. Although our sample sizes were small, this study is a first to relate coagulation times to adverse clinical signs in free-ranging birds.