Implications of prefeeding for the development of bait aversions in brushtail possums (Trichosurus vulpecula)

Cost effective control of brushtail possums (Trichosurus vulpecula) in New Zealand is currently reliant on the use of toxins, particularly aerial application of sodium monofluoroacetate (1080). However, possums' development of bait aversions threatens the continued efficacy of such control operations. Bait aversions (or shyness) have been well studied in rats (Rattus spp.), but only recently documented in possums. The aim of this study was to examine the influence of novelty, familiarity, and bait 'cues' on possums' development of aversions, in both cage and field environments. The motivation of this work was to provide better understanding of the problem and provide advice for managers undertaking possum control. The first cage trial determined the effects of prefeeding on aversion development. Three treatment groups received for 7 days either i) no prefeed ii) plain prefeed, or iii) dyed and lured prefeed baits. Each possum then ingested sub-lethal 1080 bait. Seven days later, the possums were tested for development of an aversion towards 1080 bait, a prefeed bait, and a prefeed bait containing brodifacoum. Most (96%) non-prefed possums became averse to the 1080 bait, compared with only 55% and 9% of the two prefed groups. Similarly, over 90% of the non-prefed possums were averse to prefeed and brodifacoum baits, compared to