Challenging Months in the Forest

The success of our orangutan reintroduction programs, which recommenced in February 2012, has been an amazing journey for all of us to be part of and such a joy to share our stories and lessons learned. The large majority of our orangutans have adapted well, though we have had experienced disappointments. We are continually learning so we can improve all of our processes from pre-release, release and post-release. This is the first time that orangutan reintroductions in Borneo have been so thoroughly prepared for and monitored post-release. We aim for high rates of success, and our post-release monitoring enables intervention if and when needed, but we have to be realistic in accepting that it is impossible to achieve a 100% success rate.

Natural mortality rates for wild orangutans are estimated to vary from 2-8% depending on age, with higher mortality rates occurring their first year, after independence from their mother, and after maturation for adult males. This means for every 100 orangutans we release, we would expect between 2 to 8 orangutans to die every year from natural causes. Obviously a reintroduction program should expect higher rates of mortality because of the historical backgrounds of our orangutans. The survival rate for rehabilitated orangutans released during their juvenile-adolescence years has been reportedly varied between 20-80% (Russon et al, 2009); significantly different to what we would expect within wild populations.

A rehabilitant orangutan in release site.

A rehabilitant orangutan in release site.

Following 28 months of reintroductions in Kalimantan and the release of 162 orangutans, we have recently experienced two losses in East Kalimantan, which have been difficult for all of our team members as we know each individual orangutan so well. Unfortunately these took place within a short time-frame. However, we remain committed to our task of reintroduction and post-release monitoring to reestablish new genetically viable populations of orangutans to bolster conservation of the species in the wild in the long-term.

The Departure and Return of our Orangutans

Maduri was released in Kehje Sewen Forest on March 20, 2014. Despite her best efforts to adapt in her new environment, trying several natural food and learning to live in the trees, she had faced difficulties since the beginning of her release. So the Post Release Monitoring (PRM) Team focused their efforts on closely monitoring her development daily. But on May 6, 2014 at 8.30 am, the PRM Team and the vet on duty found Maduri lying on the ground, lethargic and weak with a wound to her neck. At the time, the team was also intensively treating and caring for Kent, another orangutan who was also found with some serious injuries. So their concentration and focus were divided in two.



Our vet checked her condition and decided to evacuate Maduri to Camp 103. She immediately received intensive care including intravenous liquids and was encouraged to eat. Unfortunately, all attempts failed. Maduri sadly passed away at Camp 103 on May 7, 2014.

As the same time Kent, who was released on March 22, 2014, was found with open wounds to the nape of his neck, chest and left arm on April 30, 2014, which we believed were probably a result of conflict with another male. The PRM Team had previously witnessed a fight between Kent and Bajuri, another released male orangutan, on March 24, 2014 but no injuries had been observed.



It doesn’t take long for infections to establish in a wild setting, and in line with our procedures the vet and PRM Team decided to evacuate Kent to the acclimatization enclosure and provided intensive care. Our vet cleaned and treated his wounds daily and provided forest fruits as supplement.

His condition began to improve, he started to eat well and was very active. However, because Kehje Sewen was in fruiting season, it was swarming with bees. There were several bee hives around the enclosure and Kent’s condition worsened again due to bee stings. The bees did not just sting Kent but also stung our vet who was on site treating him. Annoyed and in pain from sting bites, Kent couldn’t help but scratch his body, which aggravated and worsened his wounds. The team tried to remove the bees through various methods but to no avail.

PRM Team decided to evacuate Kent to the acclimatization enclosure.

PRM Team decided to evacuate Kent to the acclimatization enclosure.

Just like Kent, Maduri was also suspected to have received injuries to her neck from a fight with another orangutan. Although her injuries were not as bad as Kent’s, the fight would likely have caused her significant stress, which influenced her eating patterns and left her unsure of her range.The fight could have been triggered by many things including a dispute over territory or food resources.

After the passing of Maduri, the team concentrated on Kent’s health. His wounds had significantly worsened and unfortunately the facility at camp is not adequate to support the type of intensive care he required, so for the first time in 28 months we made the decision to evacuate Kent and return him to Samboja Lestari on May 23, 2014.

6 2014.05

Our vet checked her condition and decided to evacuate Maduri to Camp 103.


Following the death of Maduri and then Kent’s evacuation to Samboja Lestari, we received another blow when the team found the remains of Wani in the Gunung Belah area on June 12, 2014. Large teeth marks indicated that Wani might have been attacked, or at least scavenged upon, by another large mammal. Clouded leopards (Neofelis diardi borneensis) occur in Kehje Sewen, although they are not known to generally attack lone adult female orangutans. However there are reports of clouded leopards attempting to take orangutan infants, for example in the Ketambe Forest in Aceh, seven rehabilitated juvenile orangutans died after attacks by clouded leopards (Rijksen, 1978). Possibly it is more than likely that Wani had died and her remains were scavenged by Bornean bearded pigs (Sus barbatus). There have been cases of this species killing (but did not prey on) several young rehabilitated orangutans in Gunung Beratus Conservation Forest, East Kalimantan, and also in Tanjung Puting National Park, Central Kalimantan.



Wani could have also have died from sickness and then nature does the rest. Likely we’ll never know. Only one fact remains, which is that Wani is very sadly no longer with us. In her efforts to adapt in her new home in Kehje Sewen, Wani showed remarkable improvement in her survival skills. She identified natural food and was feeding well, despite her reluctance to build arboreal nests. However in the last few weeks of her life, Wani had started to build her nests in the trees and we were very encouraged. The last PRM note on June 5 indicated that her behavior was improving with healthy feeding behavior and good quality nests. The team decided to leave Wani alone without our constant presence, which would have naturally changed her behavior, while the team focused on other orangutans. Sadly, we had to face her death a week later.

Wani showed remarkable improvement in her survival skills.

Wani showed remarkable improvement in her survival skills.

Working for the Best

Inevitably, the last two months have been tough for the BOS Foundation. The team is doing all they can to ensure the well-being of all of our orangutans through PRM activities but of course we cannot observe everything that happens in the wild. Orangutans often simply don’t want to be followed, which is something we expect and would be demonstrated in wild orangutans. After the death of Maduri and Wani, we are now hoping the best for Kent’s recovery. The latest report from Samboja Lestari confirmed that Kent underwent surgery on May 27 to suture his wounds and he is now receiving intensive care. He is now recovering thanks to the loving care and adequate medical facilities.

We continue to work intensively on Kent’s recovery.

We continue to work intensively on Kent’s recovery.

Maduri and Wani will always be in our hearts, and we continue to work intensively on Kent’s recovery and for the continuation of a successful reintroduction program. The teams at Samboja Lestari and in Kehje Sewen Forest have been amazing in ensuring the welfare of our orangutans! We can’t thank you enough. Last but not least we thank all of you for your ongoing support for the BOS Foundation as we work towards ensuring the long-term success of our programs.

Text: Nur Hariyanto, Syahik Nurbani, Monica Devi Krisnasari, Media R. Clemm, Paulina Wijanarko, Meirini Sucahyo, Fransiska Sulistyo, Agus Irwanto, Aldrianto Priadjati, Sri Suci Utami Atmoko, Jacqui Sunderland-Groves, Simon Husson

Photos: Agus Purniawan, Awal Choirianto, Syahik Nur Bani, Suwardy



Singleton, I., Wich, S.A., Stephens, S., Utami Atmoko, S.S., Leighton, M., Rosen, N., Traylor-Holzer, K., Lacy, R., and Byers, O (eds.). 2004: Orangutan Population and Habitat Viability Assessment: Final Report. IUCN/SSC Conservation Breeding Specialist Group, Apple Valley, MN.

Marshall, A.J., Lacy, R., Ancrenaz, M., Byers, O., Husson, S.J., Leighton, M., Meijaard, E., Rosen, N., Singleton, I., Stephens, S., Traylor-Holzer, K., Utami Atmoko, S.S., van Schaik, C.P., Wich, S.A. 2009. Orangutan population biology, life history, and conservation. In Serge A. Wich, S. Suci Utami Atmoko, Tatang Mitra Setia and Carel P. van Schaik, eds. Orangutans: Geographic Variation in Behavioral Ecology and Conservation, pp. 311-326. Oxford University Press, New York.

Russon, A.E. 2009. Orangutan rehabilitation and reintroduction: Success, failures, and role in conservation. In Serge A. Wich, S. Suci Utami Atmoko, Tatang Mitra Setia and Carel P. van Schaik, eds. Orangutans: Geographic Variation in Behavioral Ecology and Conservation, pp. 327-350. Oxford University Press, New York.





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