Orangutans swing for their dinner

Griet Scheldeman, BBC News 28 Jul 09;

The deft way that Sumatran orangutans are able to swing from branches seemingly too weak to take their weight has been described by scientists.

The animals use their hands and feet to move through the canopy in a completely different way from other primates, a team from Birmingham, UK, reports.

Sumatran orangutans have been in rapid decline and risk becoming extinct.

The scientific team said the animals' conservation could be helped by better understanding the habitat they need.

The research is published in the Proceedings of the National Academy of Sciences.

Exceptional locomotion

Bioscientist Susannah Thorpe and colleagues studied wild Sumatran orangutans as they moved through the treetops.

They showed that the tree vibrations, which could unsettle the animals' balance, were countered by their ability to move with an irregular rhythm.

The team observed how the apes managed to reach the ripe fruits at the end of narrow unstable branches without falling down, by swinging flexibly.

Unlike other primates, which move through trees at a regular pace with fixed body positions and stretched limbs, the orangutans were seen to travel both upright and horizontally, above and under branches, holding on with both their hands and feet.

And more than 29% of the time, the orangutans held on to more than four branches at once.

A key finding, said the researchers, was the realisation that Sumatran orangutans rely on woody vines, or lianas, which are often depleted in logged forests, for their exceptional style of locomotion.

The scientists believe their work is likely to aid conservation.

"If the destruction of forest land does not slow down, the Sumatran orangutan could be extinct within the next decade," Dr Thorpe said.

"Now that we know more about how they move through the trees and the unique way that they adapt to challenges in their environment, we can better understand their needs. This could help with reintroducing rescued animals to the forests and efforts to conserve their environment."