Abstract:
Behind humans, house mice are the most successful vertebrate species in terms of global distribution. Their generalist diet, behavioural plasticity and commensal relationship with humans have ensured their success in urban and natural environments. The house mouse is of conservation concern because it has known direct and indirect impacts on native flora and fauna. They are a species of interest to conservation managers because of the challenges associated with confirming the eradication of mice and of determining their presence at low densities. The primary aim of this study was to determine the population densities of mice on two off-shore New Zealand islands: Maud Island and Moturekareka Island, and determine whether the detectability of mice varied depending on monitoring device and island. Bait stations, snap traps and tracking tunnels were chosen for use in this study and are commonly used in surveillance, eradication and control programmes in New Zealand and around the world. A further aim was to construct a population structure based on tooth wear of individuals captured on each island and compare this to other, well understood mouse populations on Enderby Island and Antipodes Island. It was of interest to estimate an arrival date for the invading population on Maud Island as this is still largely unknown. Using spatially explicit capture-recapture, population densities were determined to be high on both Maud Island and Moturekareka Island. Interaction behaviour varied with device type; snaptraps were most effective, followed by tracking tunnels, with bait stations appearing to be the least likely device with which mice display would interaction behaviour. A general increase in the number of interactions with all device types was observed over the five night course of the interaction study, suggesting either a learned response to the food provided, or there was a decrease in neophobic response through the course of the study. Estimation of population structure clearly showed the seasonality associated with the structuring of mouse populations and also highlighted the difference in structure between a recently invaded island which lacked any individuals in the oldest age classes and a well-established population with a more diverse population structure. Based on molar tooth wear it was estimated that the first invaders on Maud Island arrived sometime during summer 2012-2013.