Identification of weta foraging on brodifacoum bait and the risk of secondary poisoning for birds on Quail Island, Canterbury, New Zealand

Brodifacoum is a second-generation anticoagulant used for rodent control in New Zealand. Concerns about the poisoning of non-target species have resulted in restrictions being imposed on the mainland. It is, however, still commonly employed on offshore islands. Previous research investigating the poisoning risks of brodifacoum has generally focused on birds eating brodifacoum bait (primary poisoning) or through depredation of live rodents or carrion containing brodifacoum residues (secondary poisoning).

Brodifacoum residues in possums (Trichosurus vulpecula) after baiting with brodifacoum cereal bait

The presence of brodifacoum residues in possum (Trichosurus vulpecula) livers following routine possum control was investigated. Possums were poisoned in six nature reserves in the Wellington Region, New Zealand, using cereal baits containing 20 mg kg(-1) brodifacoum dispensed from bait stations. Thirty-five surviving possums, and five dead possums were sampled from the reserves following poisoning, and their livers analysed for the presence of brodifacoum. The majority (83%) of samples contained brodifacoum at concentrations ranging from 0.007 mg kg(-1) to 6.2 mg kg(-1).