Active Choice judgement bias reflects affective indicators in bonobos

Judgement bias tasks assess the ways in which affective states influence information processing. The Active Choice task, a subtype of judgement bias task, allows researchers to distinguish between low motivation and negative mood, making it more powerful than other paradigms. However, Active Choice tasks have never been successfully applied in a population of zoo-housed primates, nor in any population of great apes. We aimed to investigate affect-derived judgement biases in zoo-housed bonobos using a novel Active Choice paradigm. Fourteen bonobos were trained on a visual discrimination Active Choice judgement bias task, with seven animals passing criteria. Outcomes of the task were compared to four quantitative affective indicators as well as one holistic qualitative welfare indicator. A sixth variable, group size, was included in the models due to the unique fission-fusion husbandry style used at the zoo. We found that animals made more pessimistic choices as the number of experimental sessions they completed increased. Furthermore, animals made more pessimistic choices on days when they spent more time performing abnormal behaviors. Conversely, animals made more optimistic choices on days when they spent more time playing and on days when their social group was larger. Our results, therefore, suggest that task responses were related to changes in affective states. Moreover, Active Choice judgement bias tasks could be useful for exploring both theoretical and applied questions about mood in bonobos.