Primates are among the most cognitively complex animals, and zoo environments that fail to challenge their intelligence cause boredom, psychological distress, and stereotypic behaviors.
Primates kept without adequate cognitive enrichment are among the most visibly suffering animals in captivity. Stereotypic behaviors like rocking, pacing, and self-directed behaviors are clear indicators of psychological distress. Zoo environments that fail to provide foraging challenges, social complexity, and problem-solving opportunities condemn primates to boredom - a state that for highly intelligent animals may involve subjective suffering comparable to solitary confinement in humans. Modern zoo standards have improved significantly, but variation remains.