The Ontogeny of the Great Call in Female Southern Yellow-Cheeked Gibbons (Nomascus gabriellae)

Abstract The study of vocal development in non-human primates is crucial to understanding developmental trajectories and distinguishing innate from acquired vocal traits. Recent studies show that young female gibbons co-sing with their mothers, but these interactions decline as females become more independent. We studied the development of the great call, including notes and twitter sounds, in five captive female southern yellow-cheeked gibbons ( Nomascus gabriellae ) from 7 months to 7 years 11 months of age and compared their great calls with those of their adult mothers. We recorded 424 great calls, of which 386 included co-singing between mothers-daughters and 38 were only mothers’ great calls. We found that features of notes (duration, number and maximum frequency) developed gradually with increasing age until females reached 6 years old (subadult), when the number of notes, maximum frequency, and total call duration did not differ significantly from those of mothers, but the twitter sound was shorter. The occurrence of twitter sounds increased from 0.7 months to 4 years of age then declined until the end of the observation period at 7 years 11 months of age. However, we did not record regular emittance of the twitter sound at any age. Co-singing interactions remained at a high level across age-classes but the time difference between between the first notes of mothers and daughters decreased in subadult females. These longitudinal findings suggest that female gibbons acquire adult great calls only after 6 years of age.