BACKGROUND

The Bornean orangutan (Pongo pygmaeus) has recently been declared a critically endangered species by the IUCN, as a result of an estimated 86% population decline over just three generations (Ancrenaz et al. 2016). The main threats causing this decline are hunting, forest fires, and loss of habitat as a result of extreme levels of deforestation, mainly for oil palm plantations. To monitor the effect of these threats on populations and whether current conservation efforts are succeeding, it is vital to accurately assess populations of orangutans across the rainforest.

However, as orangutans are rare, solitary animals, they can be troublesome to find in the jungle, making monitoring populations by directly counting individual orangutans difficult! As a result, researchers count the ‘nests‘ each orangutan builds every night for sleeping and use these to estimate population densities of areas instead. Unfortunately, these nest surveys are undertaken on foot across difficult terrain, and therefore take a long time to complete and are restricted to areas that can be easily reached by walking. This means that huge areas of forest that contain orangutans go completely unsurveyed, and all too often forest areas are cleared before they can be assessed properly.