Invasive mammal control selects for trap-recalcitrant behaviour and personality

Abstract

Kill-trapping is an important management tool for suppressing invasive mammalian predator populations in New Zealand, including the common brushtail possum (Trichosurus vulpecula). We conducted a combined field and pen experiment to test the hypothesis that intensive kill-trapping selects for survivors that differ behaviourally from the general population present before trapping begins. We installed 109 kill traps in a 120 ha forest reserve and over 20 weeks removed > 95% of the reserve’s possum population. Effort required rose from 12 trap nights per possum removed at the start of the operation to 560 trap nights per possum removed after 20 weeks of control. As the operation progressed, the estimated probability of possums being kill-trapped in the reserve declined from 0.30 to 0.15 per possum per week. Similarly, camera monitoring revealed that the average probability of a possum being killed when it encountered a kill-trap fell by 59% during the operation, indicating that the surviving population was becoming increasingly trap-recalcitrant. Behavioural testing of possums live-captured from the reserve at three time points revealed that survivors live-trapped 20 weeks into the operation were significantly shyer than those live-trapped before the operation began. In captivity, personality associated with boldness and activity/exploration was a significant predictor of whether a possum would trigger pest control devices it had not previously encountered. Heterogeneity of trappability affects the effort and cost required to eradicate invasive mammalian predators. Understanding the influence of personality on trappability is an important first step towards developing more effective methods to target trap-recalcitrant individuals.