Scientists have long known that orangutans copy physical movements of humans, but Bonnie's whistling indicates that the learning capacities of orangutans and other great apes in the auditory domain might be more flexible than previously believed, Wich said. The behavior goes against the argument that orangutans have no control over their vocalizations and the sounds are purely emotional that is, an involuntary response to stimuli such as predators.
Bonnie appears to whistle for the sake of making a sound rather than to receive a food reward or some other incentive. If asked to whistle, she is likely to oblige, another indication to scientists that she makes the sound voluntarily.
In their paper, Wich and his colleagues also shared anecdotal information about Indah, a female orangutan who lived with Bonnie at the National Zoo before moving to Great Ape Trust in 2004. Indah also began to whistle some years after Bonnie was first observed making the sound in the late 1980s, but Indah died before recordings could be made of her whistles. Scientists believe that Indah's whistling was a vocalization learned from Bonnie.
That compares with what scientists assume about social learning in wild orangutan populations. For example earlier work by Dr. van Schaik and colleagues showed that wild orangutans in one population make a "raspberry" sound during nest-making, while orangutans in another population make a "nest smack" sound when engaged in the same activity. Wich said it's unlikely that purely genetic or ecological factors explain the differences in sounds of different orangutan populations. Rather, it's more likely others copy one orangutan's innovative sound because the sound serves a function.
"This is a very strong indication that different sounds among wild populations are learned and are not purely genetically or ecologically based," Wich said. "This is a great indication that orangutans can le
|Contact: Al Setka|
Great Ape Trust of Iowa