Gibbon jumping secrets revealed

10 August 2011 Last updated at 07:30 ET By Hamish Pritchard Science Reporter

Most jumping animals are specialists, physically well adapted to the task. Fleas, locusts and frogs use their legs as springs to store energy and then fire them into the air.

But specialising like this limits their options.

Gibbons are the exception, they can swing, walk and climb, and they can jump. From a standing start, a 10m tree-to-tree leap is not a problem for the gibbon.

But they have none of the anatomical adaptations of specialist jumping animals.

A new study reveals their secret: great technique.

Gibbons are at home in the high canopy of tropical forests, but they are relatively heavy and the gaps between trees are too large to travel by swinging alone.

"Gibbons eat high quality food and need to move around a large territory quickly to find it, which involves crossing between tree crowns," said Professor Robin Crompton of Liverpool University, an author on the study.

And although jumping is dangerous - falls and broken bones are common - crossing the forest floor is more dangerous still. By living and sleeping high off the ground, they avoid the clouded leopards and pythons down below.

Motion capture

Over gibbon generations, the best jumpers have survived to pass on their talents. This new study, published today in the journal Biology Letters shows how they do it.

The researchers scanned an enclosure with lasers to build up a 3D model of the environment, then filmed a pair of gibbons in high definition as they jumped between branches.

By digitising the outline of each jumping gibbon frame by frame, they revealed how its centre of mass moved, and they calculated the forces needed to propel 6kg (a stone) of hairy ape through the air.

What they found was that, for their weight, gibbons manage to put more energy into their jumps than any known animal, five times as much as humans are able to muster.

If they jumped vertically with no run up, their centre of mass would clear 3.5m compared to humans' 60cm.

Surprisingly though, the power they need to generate from their muscles to achieve this is quite modest.

Their secret lies in a fluid, crouch-and-lunge technique. Their long, heavy arms, good for hanging from branches, act as pendulums to swing their weight forward as they uncoil from the crouch.

With long, flexible limbs and a strong torso, they get to full stretch before taking off, giving them a "push-off distance" that far surpasses other leaping primates, and is four times that achieved by humans.

This graceful technique is particularly useful given what the gibbons are jumping from: a springy branch perhaps 70m above the ground. Too much power in the push just bends or even breaks the branch.

"By pushing against the branch for longer, large works can be performed accelerating the body without requiring large powers," explained co-author Dr James Usherwood of the Royal Veterinary College in Hatfield, UK.

"Gibbons appear to hit a size 'sweet-spot', where they are big enough (helped by long arms and legs) to power jumps directly with muscle, but small enough to survive crashing about through trees. Much smaller, and they need to store energy in tendons like the smaller primates such as bush babies. Much bigger and the risk of injury becomes prohibitive - orangutans are exceedingly slow and safe," said Dr Usherwood.

Source: http://www.bbc.co.uk/go/rss/int/news/-/news/science-environment-14476383

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