Abstract:
Invasive rodents have been responsible for the extinction of many species on islands. House mouse (Mus musculus) eradication attempts have been less successful than introduced rat (Rattus spp.) eradication attempts and research is needed to identify the reasons for this disparity. We studied, and successfully eradicated, a mouse population on a small (6 ha) island in northern New Zealand in an attempt to characterise possible behavioural factors influencing eradication outcome. We monitored pre-eradication mouse movements with radio-tracking and trapping to provide guidance on gridspacing for bait stations, which are a common tool used in rodent eradication and reinvasion monitoring protocols. Mouse densities on the island were estimated during three capture-mark-recapture (CMR) sessions in January, March and May 2008. Mice were then trapped almost to extinction in August 2008 and poison baits were used to eradicate the survivors. Removal trapping data combined with WaxTag interference rates provided a final density estimate of mice in winter (August in New Zealand), the period when most eradications are attempted. Densities on the island ranged from 8.8-19.2 mice/ha, with home ranges varying from 0.15-0.48 ha. Eradication success was monitored intensively using tracking tunnels and WaxTags and was confirmed in December 2008 using a trained rodent monitoring dog. Information gathered during this study can be used to make recommendations to improve the success of future mouse eradication attempts. One of the key recommendations is to identify areas of complex habitat (such as dense ground cover) where mice may not come into contact with poison and adjust eradication methods to specifically target such areas.