Secondary poisoning of mammalian predators during possum and rodent control operations at Trounson Kauri Park, Northland, New Zealand

A poison baiting operation at Trounson Kauri Park in Northland, New Zealand using first 1080 and then brodifacoum targeted possums (Trichosurus vulpecula) and rodents (Rattus rattus, Rattus norvegicus and Mus musculus). Predatory mammals were monitored by radio telemetry during the operation. All six feral cats (Felis catus), the single stoat (Mustela erminea) and the single ferret (Mustela furo) being monitored at the beginning of the operation died of secondary poisoning following the 1080 operation. A further two cats and four stoats were monitored through the ongoing poisoning campaign using brodifacoum in a continuous baiting regime. None of these radio tagged carnivores died of secondary poisoning. However, tissue analysis of additional carnivores trapped at Trounson found that cats, weasels (Mustela nivalis) and, to a lesser extent, stoats did contain brodifacoum residues. The duration that the radio-tagged predators were alive in and around Trounson Kauri Park suggests that the secondary poisoning effect was much reduced under the continuous baiting strategy compared to the initial 1080 poison operation.