Boldness, trappability and sampling bias in wild lizards

Many studies of animal personality are completed in the laboratory with animals collected from the wild. However, there is some concern that studies that trap individuals to perform assessments of personality may not collect a representative sample of personality types, as some individuals may be trap-shy. We investigated the relationship between boldness and trappability using males of a species of lizard, the Namibian rock agama, Agama planiceps, whose boldness could be assessed in the wild prior to trapping. We observed known individuals between nine and 15 times each over several weeks, which revealed that boldness consistently differed across individuals and was not influenced by factors such as body size or environmental variables. Lizards habituated to the behavioural assay, but there was no evidence of plasticity (individual differences) in the rate of habituation. As predicted, bold individuals entered the trap sooner than shy individuals and we had higher success at trapping bold individuals. Using a simple simulation model, we show that such bias leads to underestimates of effect size and reduces the power to detect correlations between behavioural traits (i.e. behavioural syndromes). We suggest that studies that trap animals for laboratory assessments of personality may consistently underrepresent the extent of personality trait variation in the populations that they sample, and recommend that future studies either develop methods for testing personality in the field that control for obvious confounding variables or make every effort to ensure minimum bias when sampling animals for use in a laboratory setting.