Proceedings of the Vertebrate Pest Conference

The Australian brushtail possum is a pest in New Zealand, as it has caused the decline of a number of native bird species and has become the greatest barrier to the eradication of bovine tuberculosis (bTB) from livestock. As such, possum populations are reduced (i.e., controlled) at a cost of millions of dollars every year. Yet, control is still timely, costly, and not always 100% effective. Behavioral changes in possums have the potential to substantially affect the ability to control possum populations. For example, it is currently unknown whether possums change their behavior, such as den-site use, following control. How possums use dens is an important consideration in controlling bTB, as dens are a potential infection reservoir for both possums and livestock. Knowledge of any changes in den-site use may allow the design of more targeted and efficient control operations that identify potential increases in transmission risk. To investigate changes in den use due to control, possums were fitted with VHF devices, and were tracked to their den sites before and after a control operation that killed approximately 54% of the adult population. The total number of dens they used and the number of times they changed dens were recorded. Density reduction resulted in an increase in the number of times possums changed dens. However, den use was more strongly influenced by the sex of an individual, with males changing their dens more often than females. Density reduction did not appear to result in a change in the number of dens used. Instead, this behaviour was also largely driven by the sex of an individual, with males using more dens than females. This potential increase in transmission risk does not mean that control strategies should not be undertaken, but that managers should keep in mind the likely responses of possums to control and adapt their strategies accordingly. For example, control measures may need to be targeted towards those individuals that use more dens, such as males. This research also further highlights the need for efficient control that reduces populations to very low densities, to negate this potential increase in transmission risk.