Friday, August 13, 2010

New research suggests orangutans not so solitary

When British naturalist Alfred Russel Wallace arrived in Borneo's jungles 150 years ago, one of his great hopes was to see orangutans. Even he was surprised at his success, spotting the red apes feeding along river banks, swinging between branches, and staring down from trees almost the moment he arrived.

He saw 29 — shooting more than half of them and sending their skins and skeletons back home — in just 100 days, an experience shared by many other adventurers and collectors during the same period.

"Whereas some early explorers would see as many as eight orangutans in one tree or encounter 35 along a river in one day, spotting even one in the wild in the same undisturbed forests is now rare," said Erik Meijaard, one of the authors of a study published Wednesday in PLoS One, a journal of the Public Library of Science.

"This prompted us to ask if these notoriously solitary apes once lived in much higher densities," said Meijaard. "We believe hunting may have caused a change in behavior, causing them to be less social."

The scientists measured the density of orangutan populations now compared with assumed densities in past — based in part on frequency of sightings by 19th century explorers — and found that encounters were three to six times higher back then. They also looked at possible causes, including ecological changes and disease, and determined the continuing tradition of hunting was the most likely reason for the decline.

Today, orangutans are shot for their meat or as agricultural pests.

The findings are still preliminary and likely to be controversial, but if correct, they could affect the way we come to understand the development of orangutans as a species and their conservation needs.

There are only an estimated 50,000 orangutans left in the wild, all living in small, scattered populations on Borneo island and nearby Sumatra, according to Serge Wich, a scientist with the Great Ape Trust of Iowa and co-author of the new study.

Orangutans are gregarious when they are young. But unlike the other great apes — chimpanzees and gorillas — they spend most of their time alone when they are adults, foraging for fruit or sleeping in the trees. They are rarely seen together in groups larger than two or three.

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