Arboreal travel for large apes is energetically demanding and risky due to the complexity of the forest canopy. Careful selection of supports is therefore essential for safe and efficient locomotion. This thesis investigates the factors involved in route and support selection in bonobos (Pan paniscus) and in modern human (Homo sapiens) tree climbers. Naturalistically housed bonobos were given a choice of two ropes, one that provided easy access and another that required more demanding postures, with which to access a hard-to-reach food goal. The bonobos selected a rope based on its distance from the goal and its flexibility. Decision making in human tree climbers was investigated using a novel combination of qualitative (participant interviews) and quantitative (observations of behaviour) data. Participants were asked to collect goals from within a tree crown three times each. Interviews revealed that participants either considered risk avoidance or ease/efficiency as the main factor influencing their decisions whilst climbing. Those considering risk took longer to complete each climb, but became quicker after their first climb. These studies demonstrate that the demands of the arboreal environment require knowledge of the functional properties of supports and that memory of specific routes may increase the efficiency of arboreal locomotion.

An animal’s locomotor abilities facilitate its interactions with the surrounding environment. Extant hominoids (apes) have evolved diverse ranges of locomotor strategies which allow them to exploit terrestrial and arboreal habitats despite their large body size. However, hominins (modern humans and their ancestors) are traditionally defined by their restriction to upright, bipedal posture and locomotion. Reconstructions of locomotor capacity in fossil hominoids allow investigation of the evolution of extant ape locomotion; yet these reconstructions rely on detailed understanding of the relationships between morphology, locomotor behaviour and the environment in extant apes. This thesis explores variation in locomotor behaviour and skeletal morphology among extant apes in order to shed light on these relationships. Studies of chimpanzees, gorillas and modern humans reveal considerable mechanical variation in gait, and demonstrate the importance of considering environmental context in ape locomotion. Anatomical studies find reduced reliability of inferring locomotor capacity in fossil hominoids due to significant variation among extant apes in skeletal predictors of habitual bipedality and estimations of joint range of motion. These studies highlight the importance of behavioural flexibility in determining hominoid locomotor capacity, and suggest that fossil hominoids were less constrained in their locomotor repertoires than previous reconstructions imply.