The effect of enclosure structure on the positional behaviour of captive Bornean orangutans (Pongo pygmaeus)

Abstract

Orangutans (Pongo) are the largest arboreal mammals and the only great apes that spend most of their life in the trees. Wild orangutans employ a great diversity of locomotion behaviours when traversing the canopy and are rarely on the ground. However, in captivity orangutans are known to spend less time on movement and being above-ground then their wild counterparts. Additionally, captive orangutans most commonly walk around their enclosure, while wild orangutans rarely walk and predominantly use suspensory locomotion to move across the canopy. Stimulating natural locomotion behaviour can benefit captive species significantly, especially the energy efficient orangutan, as their low metabolic rates make them prone to obesity. Yet, it remains poorly understood which enclosure designs can be used to stimulate natural locomotion in captive orangutans.

Therefore, in this study different naturalistic enclosure designs were compared to study both the quantity and quality of locomotion of orangutans in these enclosures. Ten Bornean orangutans (Pongo pygmaeus) were focally observed in three enclosure types at Apenheul Primate Park (Apeldoorn, the Netherlands) and Allwetterzoo (Münster, Germany), both inside and outside. Mainly enclosure types containing many large horizontal trunks were compared with enclosures containing large amounts of ropes.

Regarding the quantity of locomotion, no differences were found between enclosures and orangutans in all enclosures moved less than their wild counterparts. However, for the quality of locomotion, slight differences were detected between the enclosure types. Mainly, orangutans used natural and challenging locomotion types, such as suspensory locomotion and climbing, somewhat more frequently in an inside enclosure with a high density of vertically aligned ropes. Our findings indicate that enclosure design does affect the types of locomotion shown by captive Bornean orangutans. Importantly, increasing the number of thin flexible substrates seems to somewhat increase the occurrence of more natural locomotion types. However, natural rates for the total quantity of locomotion, as well as the occurrence of natural locomotion types were not fully attained in any of the enclosure types studied. Therefore, while we recommend increasing the number of thin flexible substrates in captivity, further efforts are needed to stimulate orangutans towards natural locomotion patterns.