Gibbons (family Hylobatidae) are a uniform group of territorial and mostly pair-living apes that are well known for a stable patterns of vocalizations specific for species and sex (male calls in males and great calls in females). Little is known about the vocal ontogeny in males. Surprisingly, it has been shown, that immature (up to 5 years of age) Hylobates and Nomascus males produced female-like great calls during co-singing interactions with their mothers both in the wild and in captivity. Recently it has been shown that the transition from the female-like great call to the male-specific call occurred gradually. Young males (~5 to 8 years of age) in southern yellow-cheeked gibbons (Nomascus gabriellae) aged 5.6 to 7.1 years old emitted both calls (female-like great calls and male-specific calls). After 7.1 years of age, young males emitted male calls exclusively.