Secondary poisoning of stoats (Mustela erminea) in a South Island podocarp forest, 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), ship rats (Rattus rattus) and brushtail possums (Trichosurus vulpecula). Possums were an important source of the poison, with six stoats dying 1-2 weeks after scavenging on poisoned carcasses. New male stoats rapidly invaded the poisoned areas, but few were killed because poisoned carcasses were scarce. Most resident stoats died before possums were poisoned in other New Zealand trials when Talon 20 P was hand-broadcast. Prey abundance is potentially an important determinant of efficacy of the method, so pulse baiting is likely to be more successful than press (sustained) baiting operations for controlling stoats. Use of bait stations delayed indirect poisoning of stoats, but reduced risks to non-target native species compared with hand-broadcast operations. Talon 20 P poisoning operations using bait stations could be 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 should be intensively researched before the method is routinely used. This research also demonstrates the potential hazards of the new anticoagulant poisons like brodifacoum to conservation of small native predators elsewhere.