Orangutans have a lot to say. And the way they do so may be more complicated and sophisticated than previously appreciated, according to new study in PeerJ Life & Environment.

Orangutans, the great apes of Southeast Asia, have a reputation for complex vocal communication. But understanding the nuances of their repertoire has proved challenging for researchers.

Wendy Erb, a primatologist with the K. Lisa Yang Center for Conservation Bioacoustics at the Cornell Lab of Ornithology and her team sought to decipher “long calls” between orangutans. Researchers believe they use these vocalizations to communicate over long distances in the rainforests of Indonesia.

Their study didn’t examine what the primates were saying. But it helped identify how they were saying it. The researchers concluded that orangutans use a far greater variety of sounds than has been previously appreciated.

A Variety of Orangutan Sounds

To reach that conclusion, the team first recorded hundreds of long calls of 13 orangutans over about three years. But the scientific team did much more than just listen to them.

First, they broke the calls into 1,033 “pulses”— short units within a call with specific characterization, like intensity and frequency. Then they used software to examine 46 types of sound features.

The software created spectrograms — visual representations of sound waves. Then, the researcher could zoom in on parts of those waves so they could examine how those snippets both looked and sounded. They also could slow down the sounds to better identify nuances.

The team then randomized the snippets and had them examined both by three researchers and multiple “machine-learning” methods. Those approaches aimed to remove bias and find multiple ways to confirm their findings.

Pattern Recognition

Both the humans and machines hit upon the same patterns.

“We identified three distinct pulse types that were well differentiated by both humans and machines,” Erb said in a statement. “Orangutans may possess a far greater repertoire of sound types than we have described, highlighting the complexity of their vocal system.”

Erb said the technique could be used to look at sounds other animals make.

“We hope that our findings inspire further exploration of vocal complexity across different species and pave the way for future discoveries in animal communication,” she said.

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Before joining Discover Magazine, Paul spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.