The Possum Pied Piper: the development and investigation of an audio lure for improved possum (Trichosurus vulpecula) monitoring and control in New Zealand

Abstract

Improving vertebrate pest control operations relies on increasing pest animal encounters and interactions with control devices, primarily toxic baits and traps. Encounters and interactions are encouraged using a variety of baits and lures that stimulate an animal’s visual, olfactory or auditory senses, which attract and orientate the target species towards the control device. Likewise, attractants can be used to improve interaction rates with monitoring and detection devices providing more accurate estimates of the distribution and changes in the relative abundance of invasive pest species. In New Zealand, the Australian brushtail possum (Trichosurus vulpecula) is a major invasive pest of conservation and agricultural estates and is the subject of on-going management to keep population densities below environmental damage and disease transfer thresholds. Possum control operations have, traditionally, used visual and, to a lesser extent, olfactory lures for attracting possums to control devices and much research has been undertaken to make improvements to traditional lures. However, the potential for an auditory stimulus to attract possums remains largely unexamined and underutilised for possum control in New Zealand. Research presented in this thesis expands on previous studies with captive animals and examines the development and field testing of an audio lure for possum control. Preliminary field trials showed that possums found audio-lured devices sooner than silent devices, and that a greater proportion of audio-lured devices were located by possums over time. In addition, possums were recorded investigating audio-lured sites at higher rates compared to silent sites, suggesting that possums were more likely to interact with a control device if it had an audio lure. In areas where possum populations were high (>5/ha), audio lures were no better than traditional lures at attracting possums, with all sites becoming saturated by possum activity, suggesting audio lures may be most effective in areas with lower possum densities. Monitoring trials in lower density possum populations undertaken to compare the sensitivity of two detection devices to possum presence revealed that Chew-track-cards (CTCs) were more sensitive at detecting possums than WaxTags®. The palatable olfactory and gustatory peanut-butter stimulus contained within CTCs was believed to encourage possums to bite the detection device and likely contributed to their higher level of sensitivity. The addition of an audio lure increased the sensitivity of both detection devices further and made both monitoring devices equally as sensitive to possum presence. One trial also showed that possums were unlikely to make consecutive visits to detection devices for more than three nights indicating that detection devices should be checked for possum activity and follow-up possum control undertaken to remove detected possums every three nights during possum surveillance monitoring. Audio-lured bait stations spaced on 300 m grids at Mt Misery were as effective at controlling possum populations as the current best practice placement of bait stations on 150 m grids. More than 90% of possums captured within the 300 m grid had interacted with audio-lured bait stations. The large proportion of the possum population found to have interacted with audio-lured devices on 300 m grid suggests that alternative audio-lured control devices, such as multi-kill, self-setting possum traps, could be deployed at similar densities to achieve high levels of possum control. Simulated possum control operations using a possum control model developed from the outcomes of the Mt Misery field trial showed that using audio-lured bait stations on a 300 m grid also provided large infrastructure and labour cost savings. A simulation using the model to control an 81 ha effective area showed that infrastructure costs using standard best practice possum control strategies with bait stations cost 123% more than using audio lured bait stations on 300 m grids. In addition the fieldworker component of the labour costs were 1.5 times greater using standard best practice and required field staff to deliver over 100 kg more non-toxic bait than would be used on the 300 m grid. Overall, it appears that audio lures do have the potential to attract possums to control and detection devices faster, more efficiently and more conveniently than traditional visual and olfactory lures and will provide a useful tool for possum monitoring and control in New Zealand.