A barn owl feeding study with [¹⁴c]flocoumafen‐dosed mice: Validation of a non‐invasive method of monitoring exposure of barn owls to anticoagulant rodenticides in their prey

Abstract

Abstract A study was carried out to assess the feasibility of monitoring the exposure of barn owls ( Tyto alba ) to an anticoagulant rodenticide, flocoumafen, by analysis of residues in regurgitated pellets following consumption of flocoumafen‐contaminated mice. Mice were fed on a diet containing [ 14 C]flocoumafen, equivalent to 12 mg kg −1 , and killed 24 h later. A single [ 14 C]flocoumafen‐contaminated mouse was fed to each of four captive barn owls, equivalent to 0·11‐0·23 mg kg −1 per bird, followed on seven successive days by control diet (i.e. undosed mice). The [ 14 C]flocoumafen dose was eliminated by the owls over the eight‐day period in pellets (44%, range 35–55%) and faeces (18%, range 11–21%), with the highest residues being observed in samples from the first 24‐h period. Further detailed analysis of the pellets confirmed that flocoumafen residues in the first‐day pellets represented 15% (range 8–26%) of the original flocoumafen residues ingested by the barn owls. Calculations based on these data and typical flocoumafen residues in live captured rodents (following baiting) confirm that pellet residue analysis is a sensitive and appropriate method for the non‐invasive monitoring of exposure of barn owls to flocoumafen. There were no symptoms of anticoagulant poisoning in any of the birds; two of the birds were successfully paired the next season and produced fledgelings.