The biggest gibbon sings through a throat pouch as large as its head
Siamangs, the largest gibbons, carry an inflatable throat sac that swells to the size of their heads and turns their calls into booming songs. Their singing rings out across Sumatran and Malaysian forests each morning, and siamang fathers do more infant-carrying than males of any other gibbon.
This black, shaggy-haired ape lives in the rainforests of Indonesia, Malaysia and Thailand and is endangered. It stands up to about 1 metre tall and weighs as much as 14 kilograms, sometimes double the size of other gibbons, and is the only member of its genus. Its arms outreach its legs, and its face is mostly bare apart from a thin moustache. Fossils go back to the Middle Pleistocene. A second quirk gave the species its scientific name, syndactylus, meaning joined fingers: the second and third toes on each foot are partly webbed together.
Family life centres on a dominant adult male and female with their young, usually four animals and at most six, defending a home range averaging 23 hectares. Pairs are generally monogamous and spend more time close together than other gibbons do. Pregnancy lasts roughly six to eight months, and the mother carries the baby for its first year, but from about eight months the father takes over much of the carrying, with the infant returning to its mother to sleep and nurse. In southern Sumatra, where some groups include more than one adult male, infants get less male care, probably because paternity is less certain. Young adults leave home at six to eight years old.
Siamangs spend over half their waking hours resting, often lying on big branches, and grooming is a key social bond, with adult males the most active groomers. Figs are their staple among at least 160 plant species, and Sumatran siamangs eat more fruit, up to 60 percent of their diet. Seeds pass through them and are dropped up to about 366 metres from the parent tree, helping forests regenerate. They can live around 40 years in captivity.
Their future depends on forest. Palm oil plantations clearing large areas of Indonesia and Malaysia are the main threat, alongside the illegal pet trade. The wild Indonesian population was estimated at 360,000 in the 1980s, and a 2002 census counted 22,390 in Sumatra's Bukit Barisan Selatan National Park. Groups in burnt, regrown forest are smaller and lose more infants than those in intact forest.
Source: Siamang
