Prevalence of Anticoagulant Rodenticide Exposure in Red-tailed Hawks (Buteo jamaicensis) in New York State and Diagnostic Utility of Russell Viper Venom Test for Detecting Associated Coagulopathies

Anticoagulant rodenticides (ARs) continue to be used across the United States as a method for controlling unwanted rodent species. As a consequence, wild birds of prey are exposed to toxins by eating poisoned prey items. ARs prevent the hepatic recycling of vitamin K and thereby impede the post-translational processing of coagulation factors II, VII, IX, and X that is required for procoagulant complex assembly. Through this mechanism of action, ARs cause hemorrhage and death in their target species. Various studies have documented the persistence of these contaminants in birds of prey but few have attempted to use affordable and accessible diagnostic tests to diagnose exposure in free-ranging birds of prey. In our study free-ranging red-tailed hawks were found to be exposed to difethialone and brodifacoum. Eleven of sixteen (68%) livers tested for AR exposure were positive. Difethialone was found in 1/16 (6%) liver samples, and brodifacoum was detected in 15/16 (93%) liver samples. Difethialone was found at a concentration of 0.18 ppm and brodifacoum concentrations ranged from 0.003-0.234 ppm. Two out of 34 (6%) RTH assessed for blood rodenticide had brodifacoum in blood with measured concentrations of 0.003 and 0.006 ppm. The range of clotting times in the prothrombin time (PT) and Russell’s viper venom time assays for control RTH were 16.7 to 39.7 seconds and 11.5 to 91.8 seconds, respectively. No correlation was found between PT and RVVT in the control or free-range RTH, and there was no relationship found between the presence of liver anticoagulant residues and clotting times in the PT and RVVT.