The complexity of the environment provided to captive non-human primates fundamentally shapes their behavioral welfare, with barren environments causing severe welfare compromise regardless of physical health status.
Environmental complexity is a core component of primate welfare that cannot be substituted by any other single welfare measure. Primates evolved in complex, variable environments where navigation, foraging, social interaction, and problem-solving consumed much of their daily activity. Standard laboratory caging, even when meeting regulatory minimum dimensions, provides an environment of radical simplicity compared to what these animals need. The behavioral consequences — high rates of stereotypy, self-directed behavior indicating anxiety, and inactivity — are not the result of inadequate care by individual staff but of system-level failure to provide environments that meet the cognitive and behavioral needs of highly complex animals. Improving cage complexity is achievable at reasonable cost and is one of the highest-impact welfare interventions available.