The thick tropical forest on the island of Sumatra in Indonesia is home to the agile gibbon, a species of primates with a beautiful singing voice. With a flowing melody and powerful voice that can be heard within an area of several kilometers square, singing bouts can last for more than thirty minutes. Agile gibbons live in families thirty meters up in the forest canopy. They developed their singing skills to communicate with each other in the dense forest where visibility is poor. Singing is crucial when advertising their territory to other groups, when calling other members of their family, and for promoting bonding between males and females. Follow an agile gibbon family as we reveal the secret behind a pair's duet and show how parents pass on singing to their young.