Anticoagulant rodenticides in stoats (Mustela erminea) and weasels (Mustela nivalis) in England

Concentrations of six anticoagulant rodenticides were examined in the livers of stoats Mustela erminea L. and weasels Mustela nivalis L. trapped or shot by gamekeepers between August 1996 and March 1997. Residues of rodenticides were detected in nine out of 40 stoats (23%) and three out of ten weasels (30%) from five out of eight estates in central and eastern England. Bromadiolone (0.04–0.38 mg kg−1 wet wt) was detected in three stoats and one weasel, coumatetralyl (0.0085–0.06 mg kg−1) in six stoats and three weasels and brodifacoum (0.12 mg kg−1) in one stoat. One stoat and one weasel contained combinations of two rodenticides. Exposure to rodenticides was more prevalent in female stoats than in males. Rodenticides were widely used away from buildings on the sampled estates and so mustelids need not forage around buildings to be exposed. We conclude that stoats and weasels are secondarily exposed to rodenticides mainly by eating non-target species.