On the biophysics of Sumatran orangutan swaying

In almost one year of blogging here, we haven’t yet covered how the study of biophysics intersects with primatology. (Update: I realized I kinda lied, I forgot about this post on gibbon gait. Oops.)

Biophysics, in a sense, is the study of the form and function of bodies, and is formally defined as the application of the laws of physics to life processes. The ways a primate body plan is structured dictate some of the primary functions and forms of mobility. For example, humans have very robust lower-limb skeletal structures. From really dense femurs, to joints heavily padded with cartilage, our lower limbs are made to take a beating. This feature in our bodies, correlate to how we move about — bipedally.

Orangutan in TreeA new study, published in Biology Letters, studies how orangutans use the sway of branches to propel themselves from tree to tree. They already have longer arms than legs, a useful adaptation to reach from branch to branch. Also their lower limbs are as flexible as our upper ones (if not more)… Isn’t that crazy?

Swaying, as their primary form of movement is way more energetically cost effective than climbing down one tree and up the next and interestingly is seen in only Sumatran orangutans. According to a Nature news report on this study,

“These are the only primates known to live exclusively in the tree canopy, in part because of the Sumatran tiger and other predators that await them on the ground.”

Pretty, interesting tangent between this form of movement and the ecological context the orangutans live in, if you ask me.

The authors of the paper used video footage of Sumatran orangutans in movement to calculate the energy orangutans use in swings, by estimating the weight, mass, and angles observed in the films and plugging them into some classical torque equations.

After all these calculations, another interesting observation was made, about orangutans selecting for ‘stronger vertical branches nearer the tree trunk,’ so that they are less likely to snap under the weight of these big guys.

If you are interested in this publication, it’s published under this title and link, “Orangutans use compliant branches to lower the energetic cost of locomotion.”

10 thoughts on “On the biophysics of Sumatran orangutan swaying

  1. That is interesting how they are well-adapted to swinging in the trees for efficient locomotion. Sometimes it seems odd the quirks that evolution has taken. Driven to strategies to avoid predators, the weak seem to do well with increased intellegence and adapting, until perhaps they become predators of each other as humans seem to do. Some creatures adapt by jumping and swinging. But on the other hand, I wonder about those that jumped from trees and learned to glide or fly: the bat, the “flying squirrel”, and it’s hard to imagine the evolution of the flight of the dynosaurs… It is interesting that equations of the pendulum have only been solved in an approximation(as it’s actually non-linear) but work well for small arcs.

    Bi-pedal, hmm, there are lots of things that come in two’s or fours, but why is it that three eyes has never seemed to have worked very well– an eye on the back of the head would seem like a handy thing to have… But when it comes to our tools, wheels seems to work better than a four-legged cheetah. Maybe when artificial intelligence can mimic a cheetah brain we can make a car that runs on four legs, or a lost cat catcher than swings from trees as well as an Orangutan…

  2. Totally unrelated to Doug’s comment, but I was wondering if someone has, is, or plans to do a similar swing study on gibbons, specifically siamang gibbons?

    From what I have seen of them, they are prolific swingers, a bit lighter than their heavier ape counterparts, the orangutans… but I am confident they select for branches that better support their weight.

    Anyone out there studying this or know of a publication related to this?

  3. I guess the newspapers are a week or more behind everyone else, but they managed to have a snippet.

    Comment on: New York Times, May 1, 2007, p. F3, “Instead of Leaping, Sumatran Orangutans Sway From Tree to Tree.”

    Swayed by her argument
    to save energy, and
    let sleeping tigers lie,
    the Orangutan
    swayed a tree
    for Susannah K. Thorpe*
    while colleagues
    were busy
    waving at Bonobos elsewhere
    asking them if
    would be justified in
    gorilla warfare and spelling
    of the gestures noted

    *University of Birmingham in England. Gunung Leuser National Park.

  4. Kirsty, I do not have access to the entire article at this university. What I have gathered from the paper’s abstract, where the study was conducted isn’t totally clear,

    field observations suggest that some primates may be able to use support compliance to increase the energetic efficiency of locomotion. Here, we calculate the energetic cost of alternative methods of gap crossing in orangutans (Pongo abelii). Tree sway (in which orangutans oscillate a compliant tree trunk with increasing magnitude to bridge a gap) was found to be less than half as costly as jumping, and an order of magnitude less costly than descending the tree, walking to the vine and climbing it. Observations of wild orangutans suggest that they actually use support compliance in many aspects of their locomotor behaviour.”

    I’ve bolded aspects of the abstract which lead me to think these studies, calculations, etc. were done with wild orangutans. So that means we don’t have a zoo. I could be wrong, but I’m just picking that off of what I have in front of me.

  5. Pingback: Anthropology.net
  6. I have to do a report on orangutans. I was watching orangutan island on animal planet and what I found out is that they can’t swim and one drowned it was sad. He died in only 1/2 feet-that is how bad they cant swim. But This site needs to add mor einfo because I find it hard looking for good information.

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