Vocal Repertoire of Free-Ranging Infant and Yearling Tibetan Macaques (Macaca thibetana)

Vocal signals are the primary means of communication for most nonhuman primates. Quantitatively describing the vocal repertoire of specific species at specific age stages is a crucial step in studying their vocal communication, and it also provides a foundation for understanding the development and use of primate vocal signals. This study is the first attempt to establish a vocal repertoire for wild infant Tibetan macaques based on quantitative methods. We conducted continuous 5-month tracking observations on 18 wild Tibetan macaques aged 0-24 months living in the Yulinkeng A1 group (YA1 group) of the Wild Monkey Valley in Huangshan, collecting a total of 6667 vocal samples and defining common vocalization contexts in 8 categories. Through the quantitative analysis of 41 main acoustic parameters in 557 high-quality samples, we ultimately identified 10 call types (coo, loud coo, modulated tonal scream, whistle, bark, three-syllable chuck, rattle, squeal, noisy scream, and undulated scream). Four call types (three-syllable chuck, squeal, noisy scream, and undulated scream) were no longer used as the monkeys reached 14 months of age. Compared with adult individuals, there are three specific call types in the infant stage (three-syllable chuck, rattle, and undulated scream). Additionally, the vocalizations we collected from infant and yearling monkeys were mainly related to their communication with their mothers. Our study fills a gap in knowledge of the vocal behaviors of Tibetan macaques, particularly those of infants, and provides foundational data for the study of vocal development in Tibetan macaques. It also offers new perspectives on the evolution of primate vocal communication.