Gray gibbons are usually seen in groups of 3 or 4. Solitary individuals are also common. These individuals are adults who have been forced to leave the family and have not yet established their own territory. Hylobates muelleri is very territorial. About 75 percent of the home range, average size 34.2 ha., is defended.
Defense involves regular morning songs and calling at and chasing intruders.
Gray gibbins rarely resort to physical violence when defending territory. The gray gibbon is active for 8 to 10 hours per day. The animal is diurnal, rising at dawn and settling for the night before sunset. Males tend to become active earlier and for longer periods than females. Gray gibbons spend most of their day foraging in the main canopy of the forest.