Siamang Gibbon
Gibbons (/ˈɡɪbənz/) are apes in the family Hylobatidae /ˌhaɪloʊbəˈtaɪdeɪ, -diː/. The family historically contained one genus, but now is split into four genera and 17 species. Gibbons occur in tropical and subtropical rainforests from eastern Bangladesh and northeast India to southern China and Indonesia (including the islands of Sumatra, Borneo, and Java).
Also called the lesser apes, gibbons differ from great apes (chimpanzees, bonobos, gorillas, orangutans, and humans) in being smaller, exhibiting low sexual dimorphism and not making nests. In certain anatomical details they superficially more closely resemble monkeys than great apes do, but like all apes, gibbons are tailless. Gibbons also display pair-bonding, maintaining the same mate for life, unlike most of the great apes (this has been disputed by Palombit and others, who have found that gibbons might be socially monogamous, with occasional "divorce", but not sexually monogamous). Gibbons are masters of their primary mode of locomotion, brachiation, swinging from branch to branch for distances of up to 15 m (50 ft), at speeds as high as 55 km/h (34 mph). They can also make leaps of up to 8 m (26 ft), and walk bipedally with their arms raised for balance. They are the fastest and most agile of all tree-dwelling, nonflying mammals.
Depending on species and sex, gibbons' fur coloration varies from dark to light brown shades, and any shade between black and white. Seeing a completely "white" gibbon is rare.
Gibbon species include the siamang, the white-handed or lar gibbon, and the hoolock gibbons.
Whole genome molecular dating analyses indicate that the gibbon lineage diverged from that of great apes around 16.8 million years ago (Mya) (95% confidence interval: 15.9 – 17.6 Mya; given a divergence of 29 Mya from monkeys). Adaptive divergence associated with chromosomal rearrangements led to rapid radiation of the four genera 5-7 million years ago. Each genus comprises a distinct, well-delineated lineage, but the timing and sequence of divergence among these genera remains unresolved, even with whole genome data, due to extensive incomplete lineage sorting. At the species level, estimates from mitochondrial DNA genome analyses suggest that Hylobates pileatus diverged from H. lar and H. agilis around 3.9 Mya, and H. lar and H. agilis separated around 3.3 Mya. Whole genome analysis suggests divergence of Hylobates pileatus from Hylobates moloch 1.5-3.0 Mya. The extinct Bunopithecus sericus is a gibbon or gibbon-like ape which, until recently, was thought to be closely related to the hoolock gibbons.
One unique aspect of gibbon anatomy is the wrist, which functions something like a ball and socket joint, allowing for biaxial movement. This greatly reduces the amount of energy needed in the upper arm and torso, while also reducing stress on the shoulder joint. Sometimes, when a gibbon is swinging, its wrist sometimes naturally dislocate until the gibbon finishes its swing. Gibbons also have long hands and feet, with a deep cleft between the first and second digits of their hands. Their fur is usually black, gray, or brownish, often with white markings on hands, feet, and face. Some species have an enlarged throat sac, which inflates and serves as a resonating chamber when the animals call. This structure can become quite large in some species, sometimes equaling the size of the animal's head. Their voices are much more powerful than that of any human singer, although they are at best half a man's height.
The siamang, which is the largest of the 17 species, is distinguished by having two fingers on each foot stuck together, hence the generic and species names Symphalangus and syndactylus.
Gibbons are social animals. They are strongly territorial, and defend their boundaries with vigorous visual and vocal displays. The vocal element, which can often be heard for distances of up to 1 km (0.6 mi), consists of a duet between a mated pair, with their young sometimes joining in. In most species, males, and also some females, sing solos to attract mates, as well as advertise their territories. The song can be used to identify not only which species of gibbon is singing, but also the area from which it comes.
Gibbons are masters of their primary mode of locomotion, brachiation, swinging from branch to branch for distances of up to 15 m (50 ft), at speeds as high as 55 km/h (34 mph). The gibbons' ball-and-socket joints allow them unmatched speed and accuracy when swinging through trees. Nonetheless, their mode of transportation can lead to hazards when a branch breaks or a hand slips, and researchers estimate that the majority of gibbons suffer bone fractures one or more times during their lifetimes. They are the fastest and most agile of all tree-dwelling, nonflying mammals.
Gibbons' diets are about 60% fruit-based, but they also consume twigs, leaves, insects, flowers and occasionally bird eggs they find in a bird’s nest.
Most species are endangered, primarily due to degradation or loss of their forest habitats. On the island of Phuket in Thailand, a volunteer-based Gibbon Rehabilitation Center rescues gibbons that were kept in captivity, and are being released back into the wild. The IUCN Species Survival Commission Primate Specialist Group announced 2015 to be the Year of the Gibbon and initiated events to be held around the world in zoos to promote awareness of the status of gibbons.
