The link between inter-individual behavioural differences and the use of environmental enrichment by zoo-housed, yellow-breasted capuchin (Sapajus xanthosternos)

There is compelling evidence that inter-individual behavioural differences – here termed ‘behavioural distinctiveness’ – shape decision-making processes and interactions with the environment. Accordingly, we investigated whether behavioural distinctiveness influences the use of environmental enrichment (EE) components, with the aim of refining husbandry practices for yellow-breasted capuchin monkeys (Sapajus xanthosternos) in zoological settings. Employing the standard ethological approach of behavioural coding, we observed 20 capuchins housed in three groups comprising adult and juvenile males and females. Behavioural profiles were categorised into two distinctiveness dimensions: neuroticism and extraversion. To evaluate individual engagement with EE, we applied the ABA paradigm, wherein phases A1 and A2 (controls) represented standard zoo routines, while phase B corresponded to the implementation of an EE programme. Each phase spanned 10 days, and behavioural data were collected via focal animal sampling (10 minutes per animal per day), resulting in a total of 1,200 focal observations. During the environmental enrichment phase, capuchin monkeys displayed a reduction in aggressive behaviour alongside an increase in exploratory activity. However, contrary to our expectations, individuals with high neuroticism scores did not display a decrease in aggression following the introduction of EE components. Furthermore, unexpectedly, extraversion scores were not correlated with alterations in exploratory behaviour, behavioural diversity, abnormal/stereotypical behaviour, or inactivity in response to enrichment interventions. These findings suggest that environmental enrichment effectively reduced aggression and increased exploratory behaviour in yellow-breasted capuchin monkeys. However, measures of neuroticism and extraversion were not related to individual differences in behavioural change, indicating that individual behavioural profiles may not be reliable predictors of responses to enrichment interventions. The absence of aggression reduction in high neurotic individuals, coupled with the lack of an association between extraversion and exploratory behaviour, underscores the complexity of behavioural distinctiveness-enrichment interactions. Future research should explore additional factors, including social dynamics and prior experiences, that may influence behavioural responses to enrichment.