The thumb extends toward the wrist. This allows a better range of motion for traveling and feeding. Reproduction Sexual maturity is reached at about eight years of age. Hylobates concolor are monogamous and have one young every two to three years. The gestation period is between seven and eight months.
Nursing lasts about two years.
Behavior Hylobates concolor live in small family groups with the monogamous male and female and from one to four of their offspring. They are very territorial and occupy an area of about eight or nine acres, defending it from intrusion by other gibbons by very loud calls. Males also chase intruders off of the territory. The calls are also used it attracting mates or bonding with the current mate. These calls or songs are done by both the males and females.