The biggest challenge in releasing orangutans back to the wild is finding suitable forest habitats for them to live in. In order to determine the viability of a forest as a potential release area, we first need to conduct a thorough phenology survey to ensure the area has a sufficient amount of natural food available all year round.
A phenology survey involves recording data on all fruiting trees in the forest, as well as other food sources for orangutans, such as edible tree bark, shoots, foliage and insects. The survey also records the fruiting season of each fruit-tree species to ensure food availability over the changing seasons.
Some of the natural orangutan foods found in the Kehje Sewen include:
Ardisia sp. fruit, locally known as lampeni or rempeni, which resembles cherries – red, round and small.
Artocarpus sp., a variety of jackfruit related to cempedak and breadfruit.
Durian, which is known as the ‘king of fruits’. The durian variety found in the Kehje Sewen Forest has a reddish skin and is a great source of carbohydrate, fat, protein and minerals for orangutans.
Various types of forest flowers, including Ficus aurata, Lithocarpus gracilis, and Macaranga gigantea.
Certain plant shoots, such as rattan and forest-ginger shoots.
Raymond eating a ginger root (Etlingera sp.)
Termites, which are especially high in protein, found in weathered pieces of wood.
Angely eating termites
The Kehje Sewen Forest is an 86,450-hectare primary forest area rich in food sources for orangutans. From our phenology survey – which also involved tagging every fruiting tree in certain transects and recording data on their numbers and density – we discovered that almost 200 plant species grow there.
The Kehje Sewen Forest is rich in nutritious orangutan food and can sustain orangutan populations and other fauna. The difficulty involved in finding suitable release habitats for rehabilitated orangutans has forced the BOS Foundation to ‘rent’ forest areas under the Ecosystem Restoration Concession scheme since 2010. With 700 orangutans still under our care, we hope that support from the central and provincial governments of Indonesia will help the BOS Foundation secure more forest release areas.
Text by: PRM team in Kehje Sewen Forest