Abstract Orangutans are the largest arboreal mammals and the only great apes that spend most of their lives in the treetops. To navigate this environment, they use a wide range of locomotion behaviours. In zoos, however, orangutans often show increased terrestriality and rely on locomotion behaviours that are rarely seen in the wild, such as quadrupedal locomotion. These differences raise welfare concerns, as they may impair the development of their musculoskeletal system and reduce energy expenditure, thereby increasing obesity risk. Enclosure design may mitigate these effects by encouraging more species-typical locomotion. Therefore, this study aimed to investigate differences in locomotion behaviour of orangutans across two enclosure types, one with more flexible structures and one with more rigid structures. We performed focal observations of seven Bornean orangutans ( Pongo pygmaeus ) in Apenheul Primate Park (Apeldoorn, The Netherlands), recording their time budgets, types of locomotion and the structures used for locomotion. While overall time budgets, including time spent moving, did not differ meaningfully between enclosures, orangutans showed increased rates of species-typical locomotion behaviours, such as suspensory locomotion, in the enclosures with more flexible structures. Moreover, orangutans specifically used the flexible structures in their enclosure to perform these behaviours. Our findings highlight the importance of enclosure design, with flexible structures stimulating more species-typical locomotion in orangutans. However, rates of species-typical locomotion remained below those observed in the wild, indicating that further efforts are needed to stimulate zoo-housed orangutans toward natural locomotion patterns. Future research should explore additional strategies to promote arboreal and species-typical movement patterns in zoo-housed apes.
Geijtenbeek et al. (2026) studied this question.