Mitigating Observer Bias in Primate Behavioural Research: Ethogram and Circumferential Distance Analysis (CDA) Approach

Ethograms have been a standard method for describing animal behaviour, but they may be prone to observer bias, especially in field settings like ecotourism sites, where animals can react both to the stimulus and to the presence of people. In this exploratory study, we present Circumferential Distance Analysis (CDA), a prototype method designed to complement ethogram observations by quantifying approach–avoidance behaviours based on travel movements of the target organism.,We observed long-tailed macaques (Macaca fascicularis) in an anthropogenically-influenced environment setting. The ethogram allowed us to document a range of visible behaviours, but it became clear that CDA captured patterns that the ethogram missed, particularly subtle shifts in proximity to the stimulus that may signal changing interest.,CDA focuses on location and change in distance, offering a more objective perspective. Taken together, our results suggest that combining spatial analysis with traditional behavioural coding may help reduce bias and provide a clearer picture of animal decision-making, especially in environments where human presence is hard to eliminate.