There are no visible sexual swellings although the genitalia undergo color and turgidity changes that are thought to be associated with ovulation. From the limited amount of data available, there appears to be no birth seasonality or birth peak in the gray gibbon population. The gestation period is 7 months. Usually a single young is born. There is a limited amount of data on the mating of this species.
Males initiate mating more frequently than females.
If the female is willing to mate, she bends forward in acceptance. Behavior The gray gibbon is very agile. Gray gibbons travel mostly in trees by swinging from branch to branch. They move by brachiation, which means they extend their long arms over their head in order to hook their hands onto branches. The gray gibbon moves quickly with long leaps and swings.