Abstract:
The house mouse is a highly commensal rodent species that has been accidentally spread across the world by humans. Mice have significant negative impacts on the ecosystems they invade and mouse eradication is an important conservation tool. A number of mouse eradication attempts have failed for unknown reasons and basic knowledge about mouse populations on New Zealand islands was lacking so this research project was commissioned to investigate mouse biology with the aim of improving eradication attempts. A review of all mouse eradication attempts reported up to May 2007 revealed a failure rate of 38%, far higher than the 5-10% reported for invasive rat species. A series of possible reasons for mouse eradication failure were identified and these formed the basis of the rest of the research. The eradication database was updated in February 2011 and several successful eradication attempts since 2007 lead to a revised failure rate of 33%. Mouse population densities and ranging behaviour on islands were unknown so these were investigated over an 8 month period on 6 ha Saddle Island culminating in mice being successfully eradicated from the island. The worldwide distribution of mice shows they are effectively able to invade new areas but how they behave when they arrive had never been studied. In the first experiment of its kind, I experimentally released pairs of male and female mice onto Saddle Island, simulating a new invasion with each release. The released animals showed dramatic changes in behaviour which are possibly adaptations to avoid mate-finding Allee effects. Anticoagulant resistance and behavioural differences between subspecies were also identified as possible reasons for eradication failure during the database review. A phylogeographic approach was used to identify the source population and subspecies of mice obtained from island and mainland sites in New Zealand with different mouse control regimes, with the aim of identifying links between mtDNA D-loop haplotype and control outcome. Results were inconclusive but several promising avenues for further research were identified. Population genetics and trapping records were used to investigate population structure of mice living on Saddle Island prior to the eradication. Population structure was shown to change through the year and genetic analysis suggested that the population was founded by a small number of individuals. The overall conclusion of this research is that with proper planning it is possible to eradicate mice from islands and to maintain mousefree sanctuaries. A series of management recommendations drawn from this research are listed.