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Page last updated at 13:36 GMT, Wednesday, 21 July 2010 14:36 UK
How gibbons leap huge distances revealed by scientists
By Matt Walker
Editor, Earth News

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One giant leap for a gibbon (video courtesy of the University of Liverpool)

Gibbons are among nature's great acrobats, capable of leaping prodigious distances between trees, crossing gaps of more than 10m at a time.

Now researchers have worked out just how they do it.

Gibbons, it turns out, leap in four distinct ways, and will choose which to employ depending on the circumstances.

For example, they make fast, efficient leaps if they know the trees well, but make slower, more energy-sapping leaps when putting safety first.

Details of the behaviour are published in the American Journal of Physical Anthropology.

Field data from wild gibbons have reported leaps in excess of 10m, yet no detailed studies were available to document this behaviour
Anthony Channon
University of Liverpool

Gibbons, which belong to the smaller apes, are naturally great swingers, using their arms to swing from branch to branch. They are also great leapers.

They use these two forms of locomotion to move between trees and through the canopy.

That saves both time and energy as it avoids the need to climb down a tree, walk across the forest floor and climb back up a neighbouring trunk, which also places them at a greater risk from ground-based predators such as wild cats.

While gibbons tend to swing to bridge short gaps, they often leap to cover much larger ones, often gaps measuring many metres across.

"Gibbons are known to be excellent leapers and field data from wild gibbons have reported leaps in excess of 10m, yet no detailed studies were available to document this behaviour," explains biomechanics expert Anthony Channon, who is completing a PhD at the University of Liverpool, UK.

Gibbon (copyright Photolibrary.com)
Swinging isn't the only way a gibbon can travel

That is due in part because wild gibbons are so difficult to see and track in the forest foliage.

So along with colleagues at the University of Liverpool and University of Antwerp, Belgium, Mr Channon decided to study the biomechanics of leaping among a group of captive, untrained gibbons held at the Planckendael Wild Animal Park in Belgium.

Together, the researcher collected data during 24 spontaneous, unprovoked leaps made by an adult female white-cheeked gibbon (Nomascus leucogenys).

Without interfering with the ape, the researchers used a forceplate to record the forces exerted by the gibbon's feet as it leapt, and two high speed cameras to record details of its body position, and the angles of its legs, body and arms.

GIBBON FACTS

This revealed that the gibbon uses four distinct modes of leaping, categorised as the orthograde single footed take-off, the orthograde two footed take-off, the orthograde squat jump and the pronograde single footed take off.

To make an orthograde single-footed leap, which was the most common way to jump, the gibbon continued its walk taking one full stride before reaching the take off phase.

The gibbon used a similar motion to create a two footed take off, but as its name suggests, the ape placed foot feet on the ground before leaping into the air.

"The orthograde single and two-footed leaps are likely useful during feeding and crossing short distances between branches of the same tree," explains Mr Channon.

"Gibbons have been shown to jump small distances within one tree when feeding or playing."

The more energetic squat jump and the pronograde take off were each utilised to initiate about a quarter of the total number of leaps.

Squats jumps were used to leap into the air from a sitting position, and are energetically expensive. Gibbons likely jump this way when they are less certain about the tree they are jumping into, as it gives the ape time to assess what it is about to do.

Wild gibbon in Tanjung Puting, Central Kalimantan
Assessing the risk?

"This thorough assessment is probably crucial to gibbons, given the height at which they travel and the important consequences of a fall," says Mr Channon.

"Alternatively, when traversing well known routes, termed 'arboreal highways' by some authors, the gibbons could utilise the rapid pronograde single footed leaps, which cost less energetically."

Another role for the rapid pronograde leaps is as a prequel to a bout of swinging, technically known as brachiation.

"Gibbons often begin to brachiate straight from a leap and so the leap could provide the initial high velocities carried over into the brachiation bout," explains Mr Channon.

Most animals that make great leaps land feet first, but gibbons also use their forelimbs when landing, to grab onto the destination pole or branch.

To enable that, and their leap, the apes swing their arms forward as they leap, helping to drive their jump forward and up.

SOURCES

The researchers also found that the captive gibbon used relatively little power to make a leap, using a maximum recorded power while leaping of 71 Watts per kilogram.

For example, one specialised primate leaper, known as the galago, has been measured as using 540 W per kg.

That may be because the captive gibbon only leapt a distance of 1m across the experimental set up, rather than more than 10m which they are capable of doing in the wild.

"It was interesting to find that the gibbons were using distinct leap types, as this highlights the versatility of leaping as a locomotor mode," Mr Channon told the BBC.



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