Spitting orangutans solve nutty problem just the way we humans do

By Ernest Gill Jul 9, 2007, 3:39 GMT

Hamburg - Orangutans are clever enough to use water as a problem-solving tool just the way humans do, according to German experts using an experiment inspired by Aesop's fables.

When presented with a peanut floating deep down inside a transparent tube, the animals spat their drinking water into the tube to raise the treat to the top, where they could grab it.

Researchers say that the study is novel because it shows the insightful use of a liquid tool by a non-human primate. The results were published in New Scientist magazine.

Natacha Mendes at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, was quoted as saying that the idea for the study came out of a discussion with her colleagues about Aesop's fables.

The team focused on one particular story, in which a clever crow throws stones into a pitcher to elevate the water to a level where the bird can access it for drinking.

Mendes and her fellow researchers wondered whether the orangutans they worked with could have a similarly smart insight.

To test this out, the scientists presented five orangutans (Pongo abelii) with clear plastic tubes, each containing a small amount of water along with a peanut. But, to the orangutans' great dismay, the peanuts floated too far down the tube for them to reach.

The frustrated apes tried everything they could to get to the peanuts - including biting, hitting, and kicking the tube, according to the results published in New Scientist.

It only took them about nine minutes on average, though, to figure out that a little bit of extra water could do the trick. At this point the orangutans began taking mouthfuls of water from their drink dispenser and spitting the liquid into the tube, a trick that elevated the peanuts to an accessible point.

'This seems to be insightful behaviour because they haven't seen this test before,' Mendes told New Scientist. 'And as soon as they got the idea they continued to do it.'

And do it faster, Mendes added. She presented each orangutan with the peanut-containing tube 10 times. By the tenth attempt, it took the animals only 30 seconds before they started spitting water into the tube.

Researchers also conducted control experiments, including one in which they taped the peanut to the top of the tube. The orangutans did not spit into the tube, but instead simply grabbed the treat with their hands.

Mendes noted that archer fish (Toxotes jaculatrix) can spit water at flies to knock them into the water for eating. But she says the orangutans' use of water represents more sophisticated behaviour.

'There's no comparison,' she said, pointing out that the apes have a conscious idea of what they are doing and consider other options, such as kicking the tube. 'With orangutans we are talking about a flexible strategy - that's the big difference.'