The influence of illumination and moon phase on activity levels of nocturnal mammalian pests in New Zealand

Abstract

New Zealand (NZ) hosts several introduced mammalian pests that threaten native flora and fauna. Substantial time and money is spent controlling these pest populations with some success, but in order to attain the dream of a predator free NZ we must increase our effectiveness. We already know that nocturnal mammals worldwide alter activity levels in response to moon phase; understanding this behaviour can allow better control of their populations. Little is known as to how NZ’s nocturnal mammalian pest activity levels change with moon phase or nocturnal illumination levels. If we can predict when pests will be most active then the deployment of pest control and monitoring could be more efficient and effective.

The main goal of the current study was to determine how moon phase and illumination affect the activity levels of nocturnal mammalian pests. The first step in this process was to analyse two large camera trap data sets from the Blue Mountains (Otago) and Hawkes Bay to assess the response of the pests to moon phase (measured illumination data was not available for these data sets). Next, a highly sensitive light meter, a Sky Quality Meter (SQM), was tested in the dark conditions of rural Banks Peninsula (Canterbury) to assess whether it could differentiate illumination levels between moon phases and canopy covers. This device was then used in conjunction with indirect indices of activity, using Waxtags™ and camera traps, on three field sites over three months to assess activity levels. The Banks Peninsula data, as well as data from the Blue Mountains and Hawkes Bay, were analysed using a generalized linear mixed model with a binomial distribution and a logit link function.

Moon phase was not able to fully explain the variation in pest activity within the camera trap data (from Hawkes Bay and the Blue Mountains), by including measured illumination levels in the Banks Peninsula study more of the variation in the data set was explained. Overall, the most interesting finding was that illumination does impact nocturnal mammalian pests and appears to affect activity levels more than moon phase or rain. These results suggest that as illumination levels decreased, pest activity levels increased. The second major finding was that SQM’s can detect, even under very dark conditions, significant differences in illumination between moon phases and under different canopy covers. This research has several practical applications. First, SQM’s were found to measure illumination in a biologically relevant way and would be useful in further ecological studies. Second, there was an implication for pest control in that monitoring these pests should be targeted during darker conditions, such as outside of the full moon and under canopy cover. Taking illumination into account may increase the efficiency and effectiveness of monitoring and control, bringing us one step closer to a predator free New Zealand.