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Abstract
Cereal‐based bait containing 20 ppm brodifacoum was used in bait stations continuously from December 1997 to August 2000 in the Rotoiti Nature Recovery Project area, for controlling brushtail possum (Trichosurus vulpecula), ship rat (Rattus rattus), and house mouse (Mus musculus) populations. Concurrently (and before and after), baits containing brodifacoum, bromadiolone, flocoumafen, coumatetralyl, or warfarin were also used in St Arnaud village and on farms immediately adjacent to the project area. Brodifacoum residues were detected in the livers of 234 mammals from eight species, and two birds from two species captured alive, and a further seven birds from five species found dead in the project area (cause of death unknown). The highest concentration of brodifacoum residues in mammalian livers was recorded during the period brodifacoum was used in the project area. However, residues were present in the livers of some individuals at least 24 months after brodifacoum use in the project area stopped. These residues may have persisted in animals surviving brodifacoum use in the project area, and/or been transported into the area by animals moving to and from the adjacent village and farms, where brodifacoum use continued. Residues of flocoumafen, coumatetralyl, or warfarin, used only in the village and on farms, were also detected in the livers of animals captured up to at least 8 km from the nearest source. The results concur with other studies cautioning against indiscriminate or prolonged use of persistent anticoagulants for vertebrate pest control. However, the risks from such pesticides must be balanced against the demonstrable benefits of reducing pest abundance.