Observer gender and observation bias in animal behaviour research: experimental tests with red-backed salamanders

Most studies of animal behaviour are based on direct observations of behaviour in a natural or laboratory context. While the potential for observation biases has often been discussed, there have been few quantitative analyses of the kinds of biases that may affect behavioural data. We used multiple observers of aggression and foraging behaviour in red-backed salamanders, Plethodon cinereus, to investigate observation biases related to the gender of the observer. We divided observers so that half were aware of the sex of the salamanders and the other half were kept blind to salamander sex. We then used comparisons between blind and unblind treatments to determine the magnitude of observation biases. We found little evidence for bias due to differential perception of male and female animals by men and women observers (‘gender identification bias’) for any of the behaviours examined. Although the expectations of men and women about salamander behaviour did sometimes differ, we also found no evidence that observersʹ expectations affected their observations of salamander behaviour. However, for one component of aggressive behaviour and one component of foraging behaviour, men observed higher overall frequencies of behaviour than did women, regardless of the sex of the salamander. Additionally, for three components of aggressive behaviour, both men and women recorded greater frequencies of behaviour when they were aware of the sex of the salamander than when they were unaware of the salamandersʹ sex. For two components of foraging behaviour, there were no significant biases with respect to the observersʹ gender or their knowledge of the sex of the salamander. These results suggest that observation biases with respect to observer gender may exist for some behavioural variables, and that these biases may be relatively subtle. Although conducting blind experiments may eliminate some types of bias, our results suggest that behaviours should also be carefully screened for consistency and repeatability prior to formal data collection, even for blind experiments.