A release into the wild is often seen as the final chapter in an orangutan’s rehabilitation journey. After years of care and training at rehabilitation centers such as Nyaru Menteng and Samboja Lestari, learning to climb, forage, and live independently through forest school and pre-release islands, these orangutans are finally ready to return to their natural habitat.
For the conservation team, however, that moment marks the beginning of one of the most critical phases: ensuring that each individual can truly survive in the wild. Released orangutans are never simply left on their own.
Deep within the forests of Central Kalimantan, our Post Release Monitoring (PRM) team works every single day. There are no weekends here. The forest does not recognize Saturdays or Sundays, and neither does the responsibility of safeguarding lives that have just been given a second chance.
The BOS Foundation PRM team in Central Kalimantan conducts monitoring activities from several camps across release sites, ranging from the Bukit Batikap Protected Forest to the Bukit Baka Bukit Raya National Park landscape. From these modest forest camps, daily journeys begin often before sunrise, following transect paths that stretch for kilometers through dense rainforest.
Each released orangutan carries a small transmitter that emits a radio signal. This signal becomes the team’s first clue to their whereabouts.
Two PRM team members slowly walk along the transect. At the front, a tracker carries a GPS unit, antenna, and signal receiver. Every few hundred meters, they pause briefly, listening carefully for the distinctive sound from the tracking device. When the familiar “tek-tek” signal appears, the atmosphere shifts instantly. The transmitter has detected an orangutan nearby.
Yet locating an orangutan is never as simple as reading coordinates on a screen. The team relies on all their senses: scanning the canopy, noticing old nests, detecting faint scents, or listening for movement among branches high above.
And when the orangutan finally comes into view, the real work begins.
Once an orangutan is found, the team transitions from searching to observing. The antenna is folded away, tracking equipment stored, and full attention is directed toward the forest’s resident.
From the moment of encounter until the orangutan builds its night nest, every behaviour is carefully recorded. What it eats, how it moves, whether it plays, rests, or interacts with others. Even small details, such as the type of fruit selected or how it is consumed, become valuable scientific information.
Observations continue throughout the day, following the natural rhythm of the orangutan. Sometimes they feed while traveling through the canopy; other times they remain in a single tree for hours. At times, semi-wild individuals express discomfort with human presence through the distinctive “kiss squeak” vocalization.
When a mother is encountered with her infant, the team divides responsibilities. One observer follows the mother, while the other records the development and behaviour of the young orangutan. These observations help researchers understand whether survival skills are successfully passed from one generation to the next.
The working day ends only when the orangutan constructs its night nest and settles in to rest. GPS coordinates are recorded, the nesting tree identified, and the team quietly withdraws, allowing the forest to return to silence.
Monitoring orangutans means more than observing individuals. The team must also understand the condition of the forest they now call home.
Each month, phenology monitoring is conducted to assess natural food availability. Researchers observe trees along designated transects, recording the presence of young leaves, flower buds, blossoms, and ripening fruit. These data help answer a crucial question: can the forest provide sufficient food throughout the seasons? Cause a healthy forest is the foundation of successful reintroduction.
In addition, regular nest surveys are carried out to understand population density and distribution patterns. Every nest discovered offers clues about movement, habitat preference, and how orangutans use space within the forest.
Simple observations of nest structure and condition reveal surprisingly rich insights into the hidden nighttime lives of orangutans rarely witnessed by humans.
Not all orangutans are easy to find. Some travel far beyond monitoring routes or choose remote areas rarely visited by people. To support monitoring efforts, camera traps are installed at strategic locations.
These silent observers capture moments of wildlife activity often missed during direct observation. Occasionally, images reveal orangutans that have not been monitored for long periods, providing renewed hope and guiding the team’s next tracking plans.
Beyond orangutans, camera traps also record other wildlife species, demonstrating that the release ecosystem remains active and functioning.
Even after returning to camp, the work continues. All field notes are entered into research databases. Every recorded behaviour, feeding tree, and nesting location contributes to a broader understanding of rehabilitation success.
Through these data, the team can determine whether released orangutans are able to survive independently, find sufficient food, build proper nests, and eventually reproduce in the wild. Because the goal of reintroduction is not merely to release orangutans back into the forest, also to ensure they have truly come home.
Behind every individual living freely among the forest canopy lies the dedication of a team that continues to walk beneath the trees each day, searching for signals, protecting hope, and ensuring that future generations of orangutans will always have a place to live in the wild.
The Indonesian Ministry of Forestry together with the Central Kalimantan BKSDA, TNBBBR, and BOS Foundation will carry out the 47th orangutan release from the Nyaru Menteng Rehabilitation Center to TNBBBR.
BOS Foundation expands peatland conservation through the Sebangau Program in partnership with Sebangau National Park.
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