Symphalangus syndactylus (Siamang)
There is nothing in the world like the song of a family of Siamang gibbons radiating through the rainforest in the morning. Generally starting between 8:00 and 9:00 in the morning throughout the National Park, their calls, which are meant to define and defend their clan’s territory and can resonate for miles, usually begin petering off by about noon. You have never heard of a more majestic Battle of the Bands. The speed and agility with which they fly through the tree tops is a sight to behold, especially considering their size – they’re the largest of the lesser apes. Endangered due to habitat loss, they are abundant throughout Taman Gunung Leuser. Anyone who spends a night in the forest will wake up to their enchanting singing.
Siamangs don’t fly, but sometimes they seem to. That’s because of the way they move through the treetops where they live. Siamangs (pronounced SEE-uh-mongs or SEE-uh-mahngs) brachiate to get around, and they are very good at it! They hang by their arms and swing from one branch to the next to get where they want to go. It’s like swinging on “monkey bars” on a playground. When a Siamang is moving rapidly through the treetops, it will let go of one branch and “fly” through the air like an acrobat before grasping the next branch. Siamangs can also push off with their legs and jump as far as 30 feet through the air to get from one tree to another. So, Siamangs cannot fly, strictly speaking, but if you’re lucky, you could see one seeming to fly through the air, especially in their planned habitat in the Sumatra Rainforest.
Siamangs live in family groups and generally mate for life– a given male and female Siamang normally stay together for years. Their offspring stay with them for 5-7 years, until they reach maturity. A Siamang infant clings to its mother and is mainly cared for by its mother for the first 8 months, but is cared for mainly by its father in its second year of life. Wildlife biologists estimate that Siamangs live for somewhere between 25 and 40 years in the wild, and longer than that in zoos, up to 44 years. Reid Park Zoo’s male Lar Gibbon – a species closely related to Siamangs – currently is 49 years old!
Siamangs are diurnal animals – awake during the day and asleep at night. They usually wake after sunrise, spend up to an hour emitting their characteristic call to announce their territory, and then spend several hours foraging for food. Siamangs eat mainly fruit and tender leaves of bamboo and other plants, along with some insects, eggs, and occasional small vertebrates. Foraging for food requires several hours of a Siamang’s day. By eating fruit and later defecating out the seeds, they’re helping to shape their environment by spreading seeds around their habitat. In the afternoons, they usually rest, groom themselves and each other, and travel to that night’s sleeping area. Instead of lying down on a bed of leaves or branches, they sleep sitting upright in trees.