Successful aerial survey using thermal camera to detect wild orangutans in a fragmented landscape

Abstract

Asia’s only great ape, the orangutan, builds nests for the night in the upper rainforest canopy. Due to the location in the upper canopy, aerial surveys of orangutans rely primarily on counting nests. This method has come under increasing criticism, because nest decay rates can vary greatly over space and time and is depended on e.g. local climatic conditions, tree species and presence of termites and other animals. Whereas empty nests may not provide a good measure of presence, live orangutans in their nests does. Assuming the orangutan is the only animal species of the size that can be found in the upper
rainforest canopy at night, we used thermal camera fitted to a drone to successfully detect and identify orangutan in Kumai Estate, Central Kalimantan, Indonesia. Our results provide an encouraging new census platform for conservationists and park managers.