Gibbons are small apes usually live in monogamous territorial family groups typically consisting of an adult pair and 1–3 immature offspring. All gibbon species produce elaborate, loud, long, and stereotyped patterns of vocalization often referred to as songs. Gibbon songs are species-specific and usually produced early in the morning. Individuals of H. klossii and H. moloch produce solo songs; however all mated pairs of other gibbon species combine their song contributions to produce complex, but relatively stereotyped vocal interactions known as duets. Many functions have been attributed to gibbon songs. And this amazing behavior has always been one of most attractive aspects in gibbon studies.
Crested gibbon (genus Nomascus) songs are notable in several respects: (1) Mated pairs produce duet song bouts whereas only non-mated individuals appear to produce solo songs; (2) duet song bouts are male-dominated; (3) male song phrases are highly stereotyped; (4) song contributions of adults are highly sex-specific with typically no overlap between the sexes in either note repertoire or phrase repertoire. Gibbon song characters are largely genetically determined, however, they also display an impressive degree of situational variability, or flexibility, within the parameters of species-typical patterns.
To study the vocal individuality in male songs of black crested gibbons, Professor Jiang Xuelong and his PhD student Sun Guozheng from Kunming Institute of Zoology(KIZ) carried out the sound recordings at two field sites, Pinghe, Ailao Mountains, and Dazhaizi, Wuliang Mountains, both located in Yunnan province, China. A total of 127 coda phrases of 38 male songs bouts of 8 individual male gibbons were analyzed. By examining the acoustic individuality of the males, strong acoustic individuality among neighboring male gibbons both in Pinghe and Dazhaizi was found. All individuals can be identified within each site; only 1 of the 127 phrases was classified incorrectly, with most measurements contributing to the individuality. It appears that gibbon song vocalizations can be used as a vocal fingerprint to identify individuals. In contrast to the high classification accuracy among individuals in the same site, when data from both sites were combined, the classification accuracy was lower. Ten of 11 misplacements occurred between sites.
Greater vocal individuality within than between sites leads us to postulate a mechanism that enhances vocal individuality among neighboring gibbon males, which suggests that black crested gibbons may actively increase their degree of vocal individuality against that of their immediate neighbors by vocal adjustment.This is the first study of vocal individuality in male songs of black crested gibbons. This work has been reported on American Journal of Primatology: http://onlinelibrary.wiley.com/doi/10.1002/ajp.20917/pdf
