Territories are maintained by loud vocalized singing. Mated pairs produce an average of 5-6 offspring during their reproductive lifespan. There is little or no sexual dimorphism in canine size or body wt. There is little or no sexual dominance. Males are active fathers, frequently grooming and handling infants.
Males sing just before sunrise, and mated pairs sing duets during the morning.
Playback experiments indicate that females respond to calls by calling, whereas males silently approach the singing. Intergroup encounters usually involve males, who call back and forth or sit and stare at each other. Females did not have these indicators of fighting. Widowed females with offspring sometimes mimic the duet role of their dead partner, apparently to communicate to neighboring gibbons that the territory is still occupied by a mated pair. Concolor Gibbon may have infrequent polygyny.