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WASHINGTON (Reuters Life!) - Bonnie is like any other 32-year-old female orangutan in many ways. She's curious, gregarious, and likes nothing better than scouring her fellow orangutans for dead skin and parasites.
But there's one thing Bonnie does that has never been seen in an orangutan before. She whistles.
"She's been doing it for years and, we didn't realize really the significance until we started looking into other research and (found) she's the first documented, whistling orangutan that learned it on her own," said her keeper Erin Stromberg.
A video was shot at the whistling Bonnie at her home at Washington's National Zoo as part of a research project conducted late last year by The Great Ape Trust and the zoo itself.
The results were recently published in "Primates," an international journal providing a forum for studies on the relationship between primates, humans and other animals.
For great ape researchers, the results were startling.
The whistling video they believe shows that orangutans are capable of learning auditory behavior on their own and as a choice, rather than as a means to earn a reward after training.
Stromberg, who knows Bonnie well and was a key participant in the research project, says it shows orangutans could be anthropomorphically closer to humans than previously thought.
She and her colleagues believe Bonnie must have picked up the idea to whistle from previous keepers who whistled while they worked.
"It's important because there's previous studies that thought that great apes had kind of a fixed repertoire of sounds and that they didn't have voluntary control of these sounds, that they're maybe based purely on emotions," Stromberg told Reuters.
"But she has voluntary control of it and was able to develop the sound on her own and it takes a lot of control to control the breath and the lips so she's quite unique."
Researchers are keen to extend their studies to include other apes like chimpanzees and gorillas.
While scientists have known for many years that orangutans in captivity frequently copy the physical movements of humans, Bonnie's voluntary whistling opens up new doors in the auditory study of orangutan behavior. Stromberg and her fellow researchers say they hope to find other links which may help them better understand the development of human speech through evolution.
Editing by Belinda Goldsmith