In this update on our siamang project in South Sumatra we would like to bring you up to date on the first releases of rehabilitated siamang. Regular followers of our work will be aware that in 2022 we built the first rehabilitation centre in South Sumatra dedicated to the care of siamang. As with our Javan Primate Programme, our team in Indonesia have established a programme to rehabilitate siamang rescued from the illegal pet trade. Animals assessed as ready will then be released into appropriate protected areas to reinforce the declining populations in the wild.

Transporting Jon and Cimung to the release site December 2023 © The Aspinall Foundation, Indonesia 

The first release took place at the end of 2023. Jon and Cimung, had already been through the rehabilitation phase at our Javan Primate Rescue Centre before the new facility in Sumatra was built. They were translocated from Java to the new Centre in South Sumatra in late 2023 where they spent some weeks settling into their new environment before being transferred to a habituation enclosure in Isau-isau Wildlife Reserve, Lahat. On the 23rd December 2023, Jon and Cimung were released back to the wild where the monitoring team reported that they had almost immediately been singing a duet vocalization and full song. They are being monitored for as long as possible, and are currently doing well. For a short period of time the pair stayed close to the release site, but they have now extended their range to at least 10 hectares.

Jon and Cimung shortly after release © The Aspinall Foundation, Indonesia 

Since the beginning of this year two further siamang have been released at Isau-isau Wildlife Reserve. Male siamang Miko was released on 7th June 2024 followed by male Joni on the 9th September 2024.

Joni in final habituation phase at release site © The Aspinall Foundation, Indonesia

Isau-isau Wildlife Reserve was selected as the first release site due to its location and overall suitability. It is one of South Sumatra’s largest wildlife reserves at approximately 16,700 hectares. It has a rich biodiversity, including protected and endangered species of mammals, amphibians, and birds and an abundance of flora and fungi. A preliminary survey by our team indicated a few populations of siamang could still be detected, but numbers appear to be very low. 

Prior to any release a more detailed survey of specific blocks, based on the range requirements of siamang, is undertaken to ensure suitability of an area as a release site. This includes assessing the habitat distribution; the availability of food; trees suitable for sleeping; an adequate tree canopy for movement; other species present; and no, or minimal, potential for disturbance by humans or natural factors.

Plant species are one of the sets of data recorded during pre-release surveys © The Aspinall Foundation, Indonesia 

These surveys are just one of many essential components of a process that must be repeated every time an animal is ready for release. By carrying out this work our team in Indonesia are enabling primates that have suffered from the illegal pet trade to escape the misery of captivity and live in freedom, back in the wild.

Rehabilitated Siamang Back in the Wild © The Aspinall Foundation, Indonesia   

There can be nothing more rewarding than observing animals post release. It takes months of hard work from receiving a confiscated primate into rehabilitation to the point of a successful release. As our new siamang programme continues to develop we hope to see many more animals enjoying their freedom.

The Aspinall Foundation is working on this project in collaboration with the Natural Resources Conservation Agency (BKSDA) of South Sumatra and the Directorate General Conservation of Natural Resources and Its Ecosystem, Ministry of Environment and Forestry, Republic of Indonesia.