The Mechanical Behaviour of Wood in Relation to Orangutan Locomotion and Nest building

  • Adam Van Casteren

    Student thesis: Unknown


    Orangutans are the only great ape to live an almost completely arboreal lifestyle, spending the majority of their time in the canopy of the tropical forest. The orangutans' large size and habitual arboreal lifestyle means they are uniquely constrained by the mechanical properties of their canopy habitat.It is therefore necessary to have knowledge of the mechanics of trees and the wood material of which they are made in order to gain a greater understanding of orangutan ecology. This thesis begins with an investigation into the bending failure of three temperate tree species. Observations and electron microscopy of the fractures of hand bent branches were coupled with mechanical tests of the branch structures and the wood material. It was shown that the fracture mechanisms observed were related to the anatomy and consequent mechanical properties of the wood material. Light woods buckled due to their low transverse compressive strength, whilst denser woods tend to break in greenstick fracture, in which the fracture is diverted longitudinally at the midline, due to the low tangential tensile strength of the wood material. Three neotropical tree species were investigated in the same way and it was shown that all species tested failed in greenstick fracture with the modes of failure explained, at least in part by the differences in their wood anatomy and mechanical properties.These results were used to inform an investigation of orangutan nest architecture. The compliance of the nest structures was measured and the morphology, mechanical properties and modes of fracture of the nest elements were recorded. It was shown that nests were slightly more compliant where the orangutans' weight was situated. Orangutans built the structural part of the nest by selecting, half breaking and weaving together thicker more rigid branches. However, the nest lining was generally made from completely detached narrower and less rigid branches. This suggests orangutans have a degree of technical knowledge, selecting the correct material for a certain construction role. In order to achieve a greater understanding of the mechanically complex canopy substrate that the orangutan inhabits, a study in to the mechanics of the canopy substrate was performed. Direct measurements of compliance and frequency of oscillation were taken from a range of tropical branches used by orangutans. It was shown that compliance increases dramatically towards the tip of branch and that branch diameter is the most effective branch morphological trait for predicting compliance levels. This study allowed a greater understanding of how these properties may affect orangutan ecology. To address whether conditions are present for energy storage and return during bouts of orangutan bipedalism, measurements of compliance and branch oscillation times were used in conjunction with analysis of video footage of orangutans. It was found that long step times of orangutans fall between the minimum and optimum step times for energy return, calculated from mechanical properties of bipedal supports. These results were supported by videos demonstrating in-phase branch movement and step kinematics. These results suggest that local diameter is the single most useful trait to predict the strength and rigidity of tropical branches, and their compliance and oscillatory frequency. This suggests that this is the cue used by the apes, and helps validate the assumptions made by previous researchers investigating arboreal primate locomotion. They also suggest that the conditions do exist in the natural environment that may facilitate energy storage and return on compliant branches during bipedal locomotion.
    Date of Award31 Dec 2012
    Original languageEnglish
    Awarding Institution
    • The University of Manchester
    SupervisorAnthony Ennos (Supervisor)


    • Orangutan
    • Wood

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