Abstract
Reliable estimates of population growth rates and densities are fundamental for effective wildlife management programs. We assessed the precision of spotlight-counting as a technique to monitor changes in rabbit abundance by fitting simple population growth models to observed trends in spotlight-count data during an 18-month period of increase in European rabbit (Oryctolagus cuniculus) abundance at sites in North Canterbury, New Zealand. A model-selection approach identified a simple exponential population growth model, allowing the observed rate of increase to differ between spring-summer (Aug-Feb) and autumn-winter (Mar-Jul) to be an adequate description of the observed data. The exponential rate of increase (r) over the study period differed markedly between spring-summer and autumn-winter periods, and averaged 2.3 yr -1 and 2.5 yr -1 for the 2 sites monitored. We used the fitted exponential model to estimate the observation error per spotlight transect. The estimated coefficient of variation for 1 night of counting of 10-km transects was 16%. With such data and model assumptions, only a modest number of surveys would be required to detect, with a high degree of certainty, moderate changes in spotlight-count indices of rabbit abundance either by analysis of variance or log-linear regression.
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