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.

• MeSH
• Hylobatidae physiology   MeSH
• Sex Characteristics MeSH
• Aging MeSH
• Vocalization, Animal * MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

The effects of social separation, including vocalization, have been studied for a very long time in non-human primates under laboratory conditions. As part of the long-term research on the vocal behaviour of Nomascus gibbons in zoos, this study provides the first record of calls of the southern yellow-cheeked gibbon (Nomascus gabriellae) in response to involuntary separation. Our study revealed that calls were also emitted by an infant (aged 1 year 8 months), and that the acoustic structure of the infant's calls was similar to that of older individuals' calls. Separation-induced calls seem to have a shorter developmental convergence than vocalizations with a stable pattern (which are specific for species and sex). The acoustic structure of the calls reported here comprised simple syllables, and differed from the sex- and species-specific vocal patterns of this species. Our findings demonstrate a novel paradigm in this genus, and provide evidence of the ability of gibbons to express distress when socially separated.

• Keywords
• Gibbons, Nomascus, Separation call, Vocalization,
• MeSH
• Hylobatidae physiology   MeSH
• Social Behavior * MeSH
• Age Factors MeSH
• Vocalization, Animal * MeSH
• Animals, Zoo physiology   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH