Recapturing the canopy: stimulating Bornean orang-utan (Pongo pygmaeus) natural locomotion behaviour in a zoo environment.

Orang-utans are the largest mainly arboreal animal: wild orang-utans rarely come to the forest floor. In contrast, the locomotion behaviour of captive orang-utans encompasses more time on the ground and they spend less time on locomotion than their wild conspecifics. Moreover, their most frequently employed climbing postures differ from those of wild orang-utans. More natural locomotion behaviour may be stimulated by the design of appropriate enclosures. This study aimed to investigate how the design of orang-utan enclosures influences locomotion behaviour both quantitatively (i.e. time spent above ground and on locomotion) and qualitatively (i.e. types of movement). We collected continuous focal samples from 11 captive Bornean orang-utans (Pongo pygmaeus) at Apenheul Primate Park (Apeldoorn, The Netherlands). During the study, Apenheul offered two types of outdoor enclosures to their orang-utans: horizontal trunk enclosures with a relatively high number of large-diameter, horizontal tree trunks; and multiple rope enclosures with a relatively high number of small-diameter ropes. The results showed that the orang-utans’ quantitative locomotion behaviour was more natural in the horizontal trunk than in the multiple rope enclosures: they spent less time on the ground and more time on above-ground locomotion. However, the orang-utans’ qualitative locomotion behaviour seemed more natural in the multiple rope enclosures than in the horizontal trunk enclosures. This indicates that both horizontal trunks and small-diameter substrates are required to stimulate natural quantitative and qualitative locomotion behaviour. Zoos can apply our recommendations to stimulate natural locomotion behaviour in captive orang-utans, which may improve their physical condition and thereby increase their wellbeing.IntroductionWelfare of zoo animals may be improved by promoting natural behaviour (Newberry 1995; Maple 2007). The quality of the physical environment of captive animals may contribute to the amount of natural behaviour performed depending on its characteristics (Taylor et al. 2005; Maple 2007). First, the environment should mimic the natural situation of animals as much as possible (Young 2003). Second, enrichment can motivate animals to use their physical environment in a more natural way. Promoting natural behaviour in captive animals also conforms with the goal of zoos to educate visitors about the natural environment and the life history of their animals (Patrick et al. 2007; Hosey et al. 2013). Therefore, promoting natural behaviour will be beneficial for both animals and zoos. The orang-utan (Pongo spp.) is the largest arboreal mammal (Thorpe and Crompton 2009). Their arboreal habits may result from predator avoidance (Cant 1987), while foraging success and reproduction depend on above-ground positional behaviour (Cant 1992). Orang-utans comprise two species: the Sumatran (Pongo abelii) and the Bornean orang-utan (Pongo pygmaeus; Goossens et al. 2009). Both species are adapted to living in an arboreal environment: they possess long forelimbs with large hands and long fingers and short hindlimbs with hand-like feet, which facilitate quadrumanous locomotion through the forest canopy (Delgado and van Schaik 2000). Bornean orang-utan males are more terrestrial than Sumatran orang-utan males (Cant 1987), but even Bornean males spend more than 86 percent of time above the ground (Thorpe and Crompton 2009). Captive orang-utans may differ from wild conspecifics in their quantitative locomotion behaviour: it has been suggested that captive orang-utans spend a larger amount of time resting and staying on the ground than wild orang-utans, and spend