The forest chorus of South Sumatra in Indonesia has some of its finest singers back: a pair of rare Siamang gibbons, rescued from the illegal pet trade, have been released into the wild.
Siamang gibbons (Symphalangus syndactylus) are known for their distinctive large throat sacs. But their powerful, haunting voices, used for communication and marking territory, are a blessing and a curse.
“Gibbons are one of the most popular primates for pets in the illegal wildlife trade and Siamangs are one of the biggest targets because of their beautiful forest singing,” said Made Wedana, country director for the Indonesia programme of the Aspinall Foundation wildlife charity.
“All gibbons sing, but Siamangs are the loudest. They’re also very beautiful animals, and … very rare in the wild.”
Siamang gibbons are found in rainforests in Indonesia, Malaysia and Thailand. But the illegal pet trade – alongside habitat loss from plantations, mining and logging – means numbers in the wild are declining, and they are listed as endangered on the International Union for Conservation of Nature’s Red List.
In 2023, the Aspinall Foundation completed work on a rehabilitation centre in Punti Kayu, South Sumatra – the first of its kind to rehabilitate Siamang gibbons and return them to the wild. On 23 December, the first pair, Jon and Cimung, were released.
“Both of them were kept as pets. Jon’s condition was extremely bad – he had severe diarrhoea and was acutely malnourished. We were concerned he wouldn’t survive,” Wedana said.
The rehabilitation process took five years. Siamangs often have to learn how to find food in the wild and defend themselves from predators. There’s also a pair-bonding process, which gives them a better chance of surviving among other territorial gibbons in the area.
“Siamangs are monogamous – they pair for life,” said Amos Courage, director of overseas projects for the Aspinall Foundation. “But pair-bonding can be tricky. In enclosures, gibbons can seem bonded, but once released they don’t always get on.”
Wedana, who accompanied the pair to their release, said it went perfectly. “The two Siamangs took to their surroundings very naturally and in the afternoon they started calling, which is a hugely positive sign.”
The team will now monitor the gibbons on foot for about four months to make sure they are able to fend for themselves. If all goes well, other wild-born Siamangs rescued from the pet trade will be released in South Sumatra.
Siamangs are found crammed into small cages for sale, alongside other wild animals, at markets in towns and cities across Indonesia, as well as online. They are often infants, whose parents were killed so their offspring could be stolen and sold.
“It’s a miserable existence,” said Courage. “An animal used to swinging through vast primary forest is shoved in an enclosure, usually in someone’s small house in an urban area, and given completely inappropriate food.
“Sometimes they have their teeth taken out, so they’re more easily handled. They’re drugged. Their lives are severely reduced in captivity.
“It can be painful. They pick up diseases and sometimes come to us badly traumatised,” he said.
Keeping protected species is illegal in Indonesia. But enforcement of those laws is limited, Courage said, with a lack of equipped sanctuaries that can quarantine and conduct health checks on confiscated animals.
“Deforestation is also exacerbating the issue because you have people going into areas they wouldn’t have gone to before and coming across wild animals,” Courage added. “Frequently, the animals are killed and eaten or caught and sold as pets.”
The most effective way to protect Siamang gibbons is to reduce demand, Wedana added. “In Sumatra, not many people are aware of this sad situation,” said Wedana, who is helping to develop a public education project. “In the future, it will be better if there’s no need for this rehabilitation centre.”