Modes of vocal variation in Sykes's monkey (Cercopithecus albogularis) squeals

Area of Science:

• Primate vocalization
• Bioacoustics
• Animal communication

Background:

• Understanding non-human primate vocalizations is crucial for evolutionary studies of communication.
• Sykes's monkeys (Cercopithecus albogularis) produce a variety of vocalizations, including squeals, whose acoustic properties are not fully understood.

Purpose of the Study:

• To analyze the acoustic and laryngographic features of Sykes's monkey squeals.
• To identify the underlying mechanisms responsible for acoustic variation in these vocalizations.

Main Methods:

• Acoustic analysis of recorded squeals.
• Laryngographic measurements to assess vocal fold vibration patterns.
• Categorization of acoustic variations into four classes based on modification modes.

Main Results:

• Four primary modes of acoustic variation were identified: articulation (Class I), F0 inflection (Class II), turbulence (Class III), and polyphonic variation (Class IV).
• Classes I, II, and III variations resemble general sound production mechanisms in human speech.
• Class IV (polyphonic) variation, involving independent vocal fold vibrations, is unique and not observed in human speech.

Conclusions:

• Sykes's monkey squeal acoustics are shaped by distinct phonatory and articulatory processes.
• The findings suggest convergent evolution in sound production mechanics between primates and humans for certain vocalization types.
• Polyphonic variation represents a unique vocal production mechanism in Sykes's monkeys, potentially linked to specialized laryngeal structures.