Gibbon, (family Hylobatidae), any of approximately 20 species of small apes found in the tropical forests of Southeast Asia. Gibbons, like the great apes (gorillas, orangutans, chimpanzees, and bonobos), have a humanlike build and no tail, but gibbons seem to lack higher cognitive abilities and self-awareness.

They also differ from great apes in having longer arms, dense hair, and a throat sac used for amplifying sound.

Gibbon voices are loud, are musical in tone, and carry over long distances. The most characteristic vocalization is the “great call,” usually a duet in which the female leads and the male joins in with less complex notes, used as a territorial marker by both sexes.

The various species of gibbons can be divided into four genera: Hoolock, Hylobates, Nomascus, and Symphalangus.

Gibbons are arboreal and move from branch to branch with speed and great agility by swinging from their arms. On the ground, gibbons walk erect with the arms held aloft or behind. They are active during the day and live in small monogamous groups that defend territories in the treetops. They feed mainly on fruit, with varying proportions of leaves and with some insects and bird eggs as well as young birds. Single offspring are born after about seven months’ gestation and take seven years to mature.

Most gibbon species are about 40–65 cm (16–26 inches) in head and body length, but the siamang (Symphalangus syndactylus) can grow up to 90 cm (35 inches). The smaller species (both sexes) weigh about 5.5 kg (12 pounds); others, such the concolor gibbon, weigh about 7.5 kg (17 pounds). The female siamang weighs 10.5 kg (23 pounds) and the male 12 kg (26 pounds); the siamang is the only gibbon with a significant size difference between the sexes.

In the karst forest of Batu Katak we find one of the most abundant populations of Siamang Gibbons and White-handed Gibbons in the Bahorok region. These undervalued Apes, which are on the United Nations Red List as endangered species, are our conservation target. Our program focuses on the conservation of Gibbons in Batu Katak through Educational, Agroforestry and Ecotourism programs in the area.

My passion for these Apes led me to move a year ago to this village on the edge of the Gunung Leuser National Park. The village contains a 210-hectare karst forest in which 7 families of Siamang Gibbon and a minimum of 5 families of White-handed Gibbon live. Together with my local work team we monitor their positions and count individuals to ensure that the population does not decrease. Every year these incredible apes move through the forest in search of wild fruits and remain completely wild. Their eating habits based keep them away from conflicts with local farmers....

We encourage you to contact us and come to Batu Katak, where we offer you the possibility of carrying out monitoring activities in the karst forest to see these incredible Apes.