Later onset of adulthood in Western Hoolock gibbons (Hoolock hoolock)

The sexual maturity period of Western Hoolock gibbons (Hoolock hoolock) has long been considered to be between 6 to 8 years of age for both sexes. This report presents evidence from 12 captive Hoolock hoolock at the Sonja Wildlife Rescue Centre, suggesting a longer period to reach adulthood. The subjects are 6 males and 6 females gibbons, of which 3 are captive born and 9 are wild born. The data was derived from records collected at Sonja Wildlife Rescue Centre from 2009 to 2024. Out of the 10 subjects to have reached puberty, 9 subjects (90%) experienced it between 8 to 9 years of age, and 1 subject (10%) at 10 years of age; all these subjects reached adulthood one year after. Therefore, our evidence suggests that Hoolock hoolock experience puberty at the end of sub-adulthood, followed by adulthood that occurs between 9 to 11 years of age. As most of the gibbons that have been confiscated from the illegal wildlife and pet trade are infants, juvenile or sub-adults at the time of rescue, it is important to establish an accurate puberty and adulthood period to efficiently rehabilitate and prepare captive Hoolock hoolock for potential pairing and release back to the wild only after reaching adulthood i.e. at the age group of 9 to 11 years.