THE TOXICITY OF THE RODENTICIDE FLOCOUMAFEN TO BARN OWLS AND ITS ELIMINATION VIA PELLETS

In a Barn Owl feeding study, five birds were fed with flocoumafen-dosed mice for consecutive periods of one, three and six days. Following each of these periods the owls were allowed to recover on undosed diet. Four of the birds survived all the treatments, but the fifth bird, which had been moulting prior to the start of the six-day feeding trial, subsequently died from haemorrhaging five days after the final dose. During the six-day feeding trial the birds received cumulative flocoumafen doses ranging from 0.78 mg kg-1 to 1.25 mg kg-1 (0.93 mg kg-1 for the bird which died). By comparison with previous, analogous studies, flocoumafen appears less toxic to Barn Owls than brodifacoum. However, the relative toxicity of flocoumafen, bromadiolone and difenacoum cannot be ascertained from these studies because the dose rates were not comparable. Chemical analysis of regurgitated Barn Owl pellets indicated that a substantial amount (mean 27%) of the consumed flocoumafen was eliminated unchanged in the pellets during the dosing periods. After dosing ceased, the flocoumafen content in pellets decreased rapidly. These data confirm those from a preliminary single-dose study and substantiate the use of pellet analysis as a sensitive and selective method for non-invasive monitoring of the exposure of Barn Owls to anticoagulant rodenticides in their prey. Analysis of liver residues from both the owl which died and those which survived indicated that flocoumafen is slowly eliminated from this organ with a terminal elimination (beta-phase) half-life probably in excess of 100 days.