It is well known that gibbons emit a pattern of vocalizations, which is specific for species and sex. A previous study showed, however, that immature southern yellow-cheeked gibbon (Nomascus gabriellae) males produce only female-like great calls from 2.3 to 5.3 years of age in co-singing interactions with their mothers. To date, nothing is known about how the vocal repertoire of a male changes from the female-like call (great call) to the male call (staccato notes and multi-modulation phrase) during vocal ontogeny. The goal of this study was to describe the transition from the female-like great call to the male call and the ontogeny of the male call. We predicted that the transition from the female-like great call to the male-specific call and the development of the male call is a normal part of the aging proces. If this is the case, the following phenomena will occur: (a) female vocalization should no longer be produced with the mature form of the multi-modulation phrase and (b) all stages of the male vocalization should occur gradually as the young male ages. Young males regularly emit both female-like great calls and male-specific calls between the ages of 5.6 to 7.1 years. Once the young males reached 7.1 years of age, they emitted male calls exclusively, and they continued to do so until the end of the observation period (at 8.11 years of age). It was confirmed that the young males emitted only female-like great calls during periods when they produced non-mature forms of a multi-modulation phrase (Fm0,1—none or one frequency modulation in second notes). Furhermore, the decrease in the number of female-like great calls was attributed to the development of the mature form of the multi-modulation phrase (Fm2—two or more frequency modulation in second notes), which developed with age. We also confirmed that the multi-modulation phrase developed gradually, while the development of the staccato notes occurred in leaps. A multi-modulation phrase developed as the initial part of the male-specific call. It was evolved from a simpler to a more complex form as the maximum frequency and age of the young males increased. Staccato notes subsequently developed in certain young males. Possible explanations for such vocal ontogeny in young males are discussed in this work.

Production of species- and sex-specific vocalisation is a trait characteristic of all gibbons. However, the mechanisms of gibbon vocalisation ontogeny and the manner of developing sex-specific vocal patterns are not yet known. We recorded vocal behaviour of a juvenile male northern white-cheeked gibbon (Nomascus leucogenys). The male produced female-specific great calls. Out of 163 great-call sequences recorded during six sessions, the juvenile son joined in 157 cases with its own great call. In addition, we observed that the juvenile male improved the structure of great calls during the study by including the twitter part. Our results indicate an interesting pattern of vocal ontogeny in Nomascus and suggest a certain degree of plasticity in the vocal signalling in gibbons.

Knowledge about vocal ontogeny and vocal plasticity during ontogeny in primate species is central to understanding the evolution of human speech. Vocalizations in gibbons (Hominoidea) are very interesting and contain complex species- and sex-specific patterns. However, ontogeny of gibbon songs is little studied. Here, we document regular production and ontogenetic changes of female-specific “great call” in 4 immature (2 juvenile—c.a. 3 years old; and 2 adolescent—c.a. 5 years old) males of southern yellow-cheeked gibbon (N. gabriellae) over nine months. None of the males produced fully developed adult-like “great call” and little ontogenetic changes to “great calls” occurred. “Great calls” of sons were shorter, started higher and ended lower than those of their mothers. Regular production of twitter part of great call likely appears around 4th year as it was observed in adolescent but not in juvenile males.

No abstract

No abstract