Groups are made up of bonded pairs and up to three of their offspring. Gestation is just under 8 months with one offspring born. After the first birthday, mothers generally yield the juvenile's care to the male. Subadults leave the family after reaching adolescence between ages five and six. The single individuals observed in the forests are most likely subadults seeking mates, an activity which sometimes takes several years.
Full maturity is reached between ages eight and nine.
Here for Dr. Thomas Geissmann's Gibbon Network . You'll find a tremendous resource of gibbon information here including active conservation projects as well as photos and sounds. International Center for Gibbon Studies is also actively involved in gibbon conservation. A great reference book on primates is Noel Rowe's The Pictorial Guide to the Living Primates . Dr. David Macdonald's Encyclopedia of Mammals is one of the great standards for mammal information including the siamangs.