Secondary poisoning of stoats (Mustela erminea) in a South Island podocarpforest, New Zealand: implications for conservation

This study tested the efficacy of secondary poisoning using Talon 20 P-TM ( 20 ppm brodifacoum) in bait stations for killing predators in a New Zealand podocarp forest. Nine of 10 resident radio-tagged stoats (Mustela erminea) were killed after poisoning operations that killed mice (Mus musculus), sh ip rats (Rattus rattus) and brushtail possums (Trichosurus vulpecula). Poss ums were an important source of the poison, with six stoats dying 1-2 weeks after scavenging on poisoned carcasses. New male stoats rapidly invaded th e poisoned areas, but few were killed because poisoned carcasses were scarc e. Most resident stoats died before possums were poisoned in other New Zeal and trials when Talon 20 P was hand-broadcast. Prey abundance is potentiall y an important determinant of efficacy of the method, so pulse baiting is l ikely to be more successful than press (sustained) baiting operations for c ontrolling stoats. Use of bait stations delayed indirect poisoning of stoat s, but reduced risks to non-target native species compared with hand-broadc ast operations. Talon 20 P poisoning operations using bait stations could b e an especially useful way of restoring New Zealand's mainland communities of native biota because several species of predators are killed in the same operation, but potential risks to non-target native wildlife and humans sh ould be intensively researched before the method is routinely used. This re search also demonstrates the potential hazards of the new anticoagulant poi sons like brodifacoum to conservation of small native predators elsewhere.