Evrim Yazgin
Cosmos science journalist
It is well-known that orangutans are incredibly intelligent. Now scientists are beginning to unlock the mysteries of these remarkable great apes’ communication.
A new study published in the journal PeerJ Life & Environment sheds light on the complexities of Bornean orangutan vocalisations.
Understanding the nuances of orangutan communication has proven difficult.
“Our research aimed to unravel the complexities of orangutan long calls, which play a crucial role in their communication across vast distances in the dense rainforests of Indonesia,” says first author Dr Wendy Erb from the K. Lisa Yang Center for Conservation Bioacoustics at Cornell University in the US.
“Over the course of 3 years, we accumulated hundreds of long call recordings, revealing a fascinating array of vocal diversity,” Erb says.
To decipher the orangutan calls, Erb’s team combined traditional audio-visual analysis with machine-learning techniques. They studied the long calls of 13 individual orangutans, or pulses, to determine the number of pulse types present.
“Long calls are complex and variable vocalizations comprising multiple call (or pulse) types that vary within and among individuals. These vocalisations typically begin with a bubbly introduction of soft, short sounds that build into a climax of high-amplitude frequency-modulated pulses followed by a series of lower-amplitude and -frequency pulses that gradually transition to soft and short sounds, similar to the introduction,” the authors write.
Erb notes that she is not the first to study orangutan pulse types. In fact, other researchers have already come up with orangutan “dictionaries” describing different pulses.
But Erb and her colleagues found it difficult to categorise all the pulses they were hearing.
“Through a combination of supervised and unsupervised analytical methods, we identified 3 distinct pulse types that were well differentiated by both humans and machines,” Erb says. “While our study represents a significant step forward in understanding orangutan communication, there is still much to uncover. Orangutans may possess a far greater repertoire of sound types than we have described, highlighting the complexity of their vocal system.”
The study deepens our understanding of orangutan communication and highlights the complexity of vocalisations in the broader animal kingdom.
