The integration of control tools and attractants for optimising ground-based pest control : A thesis submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

The brushtail possum (Trichosurus vulpecula), a marsupial native to Australia, was widely introduced in New Zealand between 1890 and 1930 to support the booming fur industry in Australia. Before the settlement of humans in New Zealand, there were no terrestrial mammals other than bats; therefore, the local species evolved without mammalian predators. This isolation has profoundly affected native species like birds, invertebrates, and reptiles. Forty of the ninety-one land bird species are now extinct, and many others are in severe decline. The government's initiative to eliminate New Zealand's predators (possums, rats, and mustelids) by 2050 has significantly expanded conservation control efforts in recent years. In New Zealand, predator control has been practised for a long time, but simple trapping has since developed into a thriving industry full of expertise, including species-specific attractants. The number of traps and bait stations needed to be set up, and the associated labour and expense would be significantly reduced if animals could be reliably drawn from a distance to a bait station or trap. Research presented in this thesis expands on previous studies with captive and wild animals, identifying the attractiveness of novel multi-sensory lures for possum control. Audio lures are increasingly becoming a popular attractant for pest control in New Zealand as they can draw the animals' attention from further away and potentially become a long-lasting lure. 50% of possums were trapped at traps playing the aggressive possum audio in the winter 2022 trials; however, the attraction towards the aggressive possum audio was not reflected in the autumn 2023 trial replicate, as 57% of possums were trapped at the beep audio traps compared to the aggressive and distressed possum audio and the control. In a subsequent field trial, a newly developed audio-visual lure (AVL) device was evaluated, which emitted the aggressive possum audio. The results demonstrated that it effectively attracted possums to a live-capture cage trap, compared to an existing audio lure. Visual lures are a tried-and-true attractant for possum control in New Zealand, with the flour blaze being a commonly used attractant. However, weather can easily impact flour blaze and may not last long in suboptimal conditions; therefore, identifying a long-lasting visual lure would be an advantage. A trial with captive animals compared a photoluminescent strip, white constant LED light, white flashing LED light and control (no visual lure). Whilst there was no significantly better visual lure overall, the constant LED light treatment had the most encounters (visits within 1 m of the trap). While the lures were under development, Pest Free Banks Peninsula was given assistance for their upcoming control operations, focusing on collecting data on possum home ranges in these habitats. Understanding the size of these home ranges is crucial for optimal device spacing in line with the PFNZ2050 goal of elimination. Possums living in different habitats can have different home range sizes and population densities, especially for individuals living along/in the sea cliffs. Six GPS-collared possums deployed in Le Bons Bay, Banks Peninsula, were retrieved, identifying a significant degree of overlap between the individuals and small home range sizes (average of 2.65 ha) compared to other studies on Banks Peninsula (average of 6.2 ha). The results indicated that possums did not move far from resources or capture locations, and 100x100 m device spacing was sufficient. Complementary research on captive hedgehogs identified the most attractive food-based lures being peanut butter, rabbit meat and salmon, which had significantly more activity than egg, huhu grub, mayonnaise, male hedgehog odour, female hedgehog odour and ferret odour. However, combining the most attractive food-based lures of rabbit meat with a predator (ferret) pheromone (scent) lure worked better when compared to the food-based options on their own (freeze-dried salmon and rabbit meat). Due to the positive results from the hedgehog combination lure trial, this methodology was then applied to free-ranging possums using the best performers from the earlier captive studies being combinations of audio (aggressive possum audio), visual (constant LED light) and scent lures (conspecific bedding material). Overall, there was no significant difference between the treatments; however, the combined audio-visual treatment had the most interactions (animals in traps) and encounters (visits within 1 m of the trap), and possums also spent more time in the encounter zone for audio-visual-scent lure sites. In conclusion, these results indicate that combination lures have the potential to increase possum encounter and interaction rates around traps. The results also highlight the need for pest control managers to be flexible and choose lures that will be the most attractive to individuals at specific times of the year to ensure ongoing success. Adopting a strategic approach to lure selection can significantly enhance the effectiveness of pest control efforts and support the Predator Free 2050 goal.