Orangutans have the longest inter-birth interval, and the longest period of infant dependence, of any land mammal. This period of dependence and mother-infant bond is essential if young orangutans are to learn how to survive in the forest, and what foods to eat. In many ways, the orangutan species’ semi-solitary nature makes it easier to rehabilitate and reintroduce them into the wild, as unlike group-living primates, we do not need to establish social groups in captivity, and can release them as soon as we are confident they have learnt the skills necessary to survive. Learning these skills however, is incredibly difficult, and replicating this intense mother-infant bond the priority for all rehabilitation programmes.
As soon as orangutans arrive at our centre, they are placed in quarantine for 8 weeks. Orangutans are closely related to humans and they are susceptible to many human diseases. As almost all the rescued orangutans arrive at our centre from human-dominated landscapes, disease transmission is common, and there is a possibility of such diseases spreading throughout the centre. All orangutans are given a risk assessment and tested for more than 40 diseases, including those of bacterial, viral, parasitic, and fungal origin.
After being declared disease free, the orangutan is moved to the enclosure appropriate for its age and skill level. Very young baby orangutans are first taken to our pre-school, a forest enclosure where they can mix with other orangutans of the same age, and where dedicated Indonesian staff act as surrogate mothers, caring for them, feeding them, and encouraging them to spend time in the trees. Most orangutans in this stage are under two years of age, and although very young, some of the braver orangutans will sometimes stay in the forest overnight; the others return to their cages.
Orangutans of between the ages of two and four are taken to our baby school, where they spend time in a separate forest enclosure, and are encouraged to live more independently, making nests, spending more time off the ground and foraging for their own food. We also encourage the orangutans to spend the night in the forest, although we always allow orangutans back in to the cages if that is what they prefer.
Forest school is the next stage, where orangutans over the age of four are housed. Orangutans here have already gained independence from their keepers, and spend more time alone or with other orangutans. They stay in the forest overnight, and we encourage nest building behaviour. All orangutans at our centre in the final stages of rehabilitation are monitored, and data is collected and later analysed and compared to data from wild orangutans, to select the most appropriate candidates for release. Behavioural data collection starts in forest school.
After graduation from forest school, orangutans are moved to one of our four islands. These islands are demarcated by fences or moats and mimic, as much as possible, wild forest into which orangutans will eventually be released. Here orangutans develop their nest building and foraging skills, and are monitored from dawn to dusk. The most competent orangutans are selected for release. Once selected, orangutans are fitted with microchips for tracking post-release, and taken to our release sites.
As rehabilitation is so complex, and little is known about survival rates of released orangutans, despite orangutans having been released for over 40 years, we constantly review and refine our methods, taking into account the latest research, and our successes and failures. We hope that our methods fully equip our orangutans for future life in the wild.