The hidden rhythm in orangutan long calls

By Chiara De Gregorio,  Chiara.De-Gregorio@warwick.ac.uk

Orangutans are often described as the “quiet giants” of the Southeast Asian forests. Yet adult males produce one of the most powerful vocal signals in the animal kingdom: the long call. These calls can travel for hundreds of meters through dense vegetation and play a crucial role in orangutan social life. They help males announce their presence, maintain spacing, avoid rivals, and attract potential mates in an environment where individuals rarely meet face to face.

To the human ear, a long call may sound like a booming, continuous sequence of pulses: impressive, but not obviously “musical.” But when we examine its structure, a fascinating pattern emerges. In our study, we investigated how the temporal ratios between different parts of the call change over time. Rather than measuring each pulse in isolation, we looked at how the timing of one element relates to the next, a way to capture the underlying organization of the sequence.

What we found is that orangutan long calls are highly isochronous (like a ticking of a metronome) and display a clear double-meter rhythmic structure, an organization in which two levels of temporal regularity coexist, something rarely observed in non-human primates. In the orangutan long call, this double-meter pattern emerges from the coordination between the pulses of the call and the animal’s breathing cycles.

In other words, the rhythm is not simply produced by the vocal folds: it is tightly linked to active respiratory control, showing that orangutans manage both vocal timing and breathing in a highly coordinated way. The rhythm of a long call is not entirely fixed: orangutan long calls show a dynamic temporal pattern, not a rigid or purely repetitive tempo. Such progression may reflect physiological constraints, energetic effort, or the increasing respiratory demand of sustaining a long, high-amplitude call.

These findings offer a new perspective on orangutan communication. Rather than being simple or monotonous, long calls have internal rhythmic architecture that evolves over time and includes features uncommon in other primates. Understanding these temporal patterns not only enriches our knowledge of orangutan behaviour but also helps illuminate how rhythm and timing function in the vocal communication of other mammals. By analysing calls through temporal ratios, we can uncover structural features that are not obvious to the ear, features that may reveal how complex vocal patterns evolve.

Recognizing the rhythmic sophistication of orangutan long calls reminds us how remarkable and vulnerable these apes are. By revealing the complexity of their communication, our findings help strengthen awareness and support for protecting both the species and the forests that sustain them.