Responses to direct versus indirect cues of predation and competition in naïve invasive mice: implications for management

Many populations of invasive mice Mus musculus in New Zealand have experienced the removal of mammalian predators and competitors, with the consequence of mouse population irruptions. The effects of these removals on mouse foraging are largely unknown, yet this information is essential for developing and implementing better mouse control. We investigated the effects of direct and indirect predatory cues on foraging of free-ranging mice at a site where mammalian predators were eradicated 5 years previously. We used 17 stations, each containing four trays of millet seeds mixed thoroughly in sand, with three unfamiliar mammalian (a predator, a competitor, and a herbivore) odour treatments and a control (water), during the four phases of the moon. We measured mouse selectivity for treatment/control trays, giving-up densities (GUDs, a measure of food consumption), and tray encounter rates. Foraging by mice was not affected by odour cues from any of the unfamiliar mammals. Moonlight intensity, however, affected mouse foraging, with higher GUDs being recorded on brighter moon phases (full and waxing > new and waning) during the first night of the trials. This effect was less pronounced during the second night. Resource encounter rates were also affected, with the proportion of trays foraged lower during the brighter phases of the moon on both the first and second nights. We suggest that coordinating management efforts according to the phases of the moon has the potential to improve mouse control and reduce bait wastage.