Mooning! Is the effectiveness of possum control in New Zealand influenced by the level of nocturnal illumination?

Abstract

Background: The introduced brushtail possum (Trichosurus vulpecula) is a nocturnal herbivore, which is a major conservation, economic and epidemiological pest in New Zealand. In a response to these issues, various agencies seek to maintain possum populations at low densities primarily using toxic baiting.

International research indicates that animal nocturnal activity may be influenced by the intensity of nocturnal illumination (generally correlated with moon phase). It is likely that this effect is a trade-off between predation risk and foraging efficiency. Accordingly, the aim of this research study was to build up a quantitative record of possum foraging activity (i.e. toxic bait consumption) under varying light conditions.

Methods: Possum foraging activity was monitored using bait-feeding stations (with one station located within the forest directly compared with another station located on the forest-pasture margin). These bait stations were attached to an electronic scale and data logger (also fitted with a light, humidity and temperature recorders).

Results: Data collected thus far indicates significant differences (of up to 30%) in possum bait consumption under varying light conditions (full moon vs. new moon). This effect is not significantly influenced by other environmental factors, such as temperature and/or humidity.

Conclusions: This trial is ongoing and we are about to assess whether this result is consistent over the winter months. It is likely that during the spring and summer, there will be less cloud cover and hence the nocturnal light levels should be significantly brighter then the winter months; however, this hypothesis needs to be quantified in the field.