Validating two methods for monitoring population size of the European rabbit (Oryctolagus cuniculus)

Abstract

Two methods commonly used to monitor population sizes of the wild European rabbit (Oryctolagus cuniculus) are spotlight transect counts and active burrow-entrance counts. The accuracy and precision of these techniques were assessed by comparing monitoring data with population estimates derived from intensive observation of a tagged rabbit population near Melbourne, Australia. Both monitoring methods proved capable of yielding population indices linearly related to population density and robust to seasonal changes in population dynamics. The influence of environmental and temporal variables on rabbit emergence, and hence on spotlight transect data, was also investigated. By using data collected over a wide range of weather conditions, 55% of the variation in evening emergence behaviour of rabbits could be predicted by environmental and temporal factors, with solar time, precipitation, air temperature and wind speed accounting for most of this. However, the precision of spotlight transect count data, which are routinely collected at a fixed time of night under mild weather conditions, was not improved by attempting to correct for the effects of weather and time on emergence; continuing to conduct counts under such conditions was supported as a reliable practice.