The tree canopy is an energetically challenging environment to traverse. Along with compliant vegetation, gaps in the canopy can prove energetically costly if they force a route-extending detour. Arboreal apes exhibit diverse locomotion strategies, including for gap crossing. Which one they employ in any given scenario may be influenced by the energy costs to do so, which are affected by the details of the immediate environment in combination with their body size. Measuring energetics of arboreal apes is not tractable, thus our knowledge in this area is limited. We devised a novel, custom-made experimental setup to record the energy expenditure of parkour athletes tree-swaying, jumping, and vertical-climbing. The latter strategy was vastly more expensive indicating that when energy economy is the focus arboreal apes will prioritise routes that limit height changes. Whether tree-swaying or jumping was most economical for the athletes depended upon interactions between tree stiffness, the distance to cross, number of tree-sways required and their own mass. Updated analysis of previous inter-specific correlations suggests that whether the relative costs to vertical climb are size-invariant across primate species is complicated by details of the climbing context.
© 2016 The Author(s) Published by the Royal Society. The attached document (embargoed until 23/11/2017) is an author produced version of a paper accepted for publication in Biology Letters, uploaded in accordance with the publisher’s self- archiving policy. The final published version (version of record) is available online at http://rsbl.royalsocietypublishing.org/content/12/11/20160608. Some minor differences between this version and the final published version may remain. We suggest you refer to the final published version should you wish to cite from it.