US Geological Survey


Date of this Version



Ecotoxicology (2015) 24:720–734


U.S. Government Work


Despite widespread use and benefit, there are

growing concerns regarding hazards of second-generation

anticoagulant rodenticides to non-target wildlife which

may result in expanded use of first-generation compounds,

including chlorophacinone (CPN). The toxicity of CPN

over a 7-day exposure period was investigated in American

kestrels (Falco sparverius) fed either rat tissue mechanically-

amended with CPN, tissue from rats fed Rozol bait

(biologically-incorporated CPN), or control diets (tissue

from untreated rats or commercial bird of prey diet)

ad libitum. Nominal CPN concentrations in the formulated

diets were 0.15, 0.75 and 1.5 µg/g food wet weight, and

measured concentrations averaged 94 % of target values.

Kestrel food consumption was similar among groups and

body weight varied by less than 6 %. Overt signs of

intoxication, liver CPN residues, and changes in prothrombin

time (PT), Russell’s viper venom time (RVVT)

and hematocrit, were generally dose-dependent. Histological

evidence of hemorrhage was present at all CPN dose levels, and most frequently observed in pectoral muscle and heart. There were no apparent differences in toxicity

between mechanically-amended and biologically-incorporated

CPN diet formulations. Dietary-based toxicity reference

values at which clotting times were prolonged in

50 % of the kestrels were 79.2 µg CPN consumed/kg body

weight-day for PT and 39.1 µg/kg body weight-day for

RVVT. Based upon daily food consumption of kestrels and

previously reported CPN concentrations found in small

mammals following field baiting trials, these toxicity reference

values might be exceeded by free-ranging raptors

consuming such exposed prey. Tissue-based toxicity reference

values for coagulopathy in 50 % of exposed birds

were 0.107 µg CPN/g liver wet weight for PT and

0.076 µg/g liver for RVVT, and are below the range of

residue levels reported in raptor mortality incidents

attributed to CPN exposure. Sublethal responses associated

with exposure to environmentally realistic concentrations

of CPN could compromise survival of free-ranging raptors,

and should be considered in weighing the costs and benefits

of anticoagulant rodenticide use in pest control and eradication