Orangutans show active voicing through a membranophone.

Area of Science:

• Primate vocalization
• Bioacoustics
• Evolution of speech

Background:

• Active voicing, or voluntary control over vocal fold oscillation, is crucial for human speech.
• While nonhuman great apes can learn novel calls, evidence for active voicing has been debated.
• Previous studies may have underestimated great ape vocal abilities due to experimental design.

Purpose of the Study:

• To investigate active voicing in orangutans using a novel diagnostic test.
• To determine if orangutans can produce species-atypical vocalizations voluntarily.
• To explore the potential for vocal plasticity and learning in great apes.

Main Methods:

• Six orangutans were given access to a membranophone, a voice-activated musical instrument.
• No specific training was provided; participants used the instrument ad libitum.
• Vocalizations produced were analyzed for novelty, individual specificity, and adaptive control.

Main Results:

• Three of six orangutans produced novel, species-atypical vocalizations.
• Two orangutans successfully used their novel calls with the membranophone, confirming active voicing.
• Within an hour, subjects demonstrated adaptive voice control, altering duration and frequency to optimize instrument activation.

Conclusions:

• Active voicing, beyond species-typical repertoires, is not unique to humans among great apes.
• Individual differences in vocal proficiency and appropriate test difficulty are critical for accurate assessment.
• Experience with novel tools can reveal significant vocal plasticity and control in orangutans.