Brodifacoum residues in target and non-target animals following large-scale poison operations in New Zealand podocarp-hardwood forests

Ship rats in a North Island podocarp-hardwood forest were poisoned using brodifacoum in cereal baits presented in bait stations. Livers from 68% of 25 rats captured during and up to three months after poisoning contained brodifacoum residues. Following a rat- and possum-poisoning operation in another podocarp forest, 78% of 40 stoats, 71% of 14 weasels, and 56% of 16 ferrets trapped contained brodifacoum residues. Residue levels in stoats were greater during the three months following the removal of baits than during the poison operation. Female stoats were more likely to contain brodifacoum residues than males, perhaps the result of differences in the dietary habits of the sexes. Brodifacoum was also detected in the livers of the only morepork and in two out of 10 magpies sampled by shooting, but was absent from the livers of four robins, five tomtits, six whiteheads, one bell-bird, one fantail, one harrier and four red deer. All five pigs and two cats either shot, caught or found dead contained the toxin residues. This study emphasises the potential ecological and human health risks that flow-on from the use of anticoagulant poisons in New Zealand forests.