Orang-utan tool-use at Tanjung Puting Reserve, Central Indonesian Borneo (Kalimantan Tengah)

Abstract

During a continuing nine year study at Tanjung Puting Reserve, Central Indonesian Borneo, wild orang-utan tool-use was generally limited to two contexts: (1) agonistic displays and (2) nesting/covering behaviors. As in other areas of Borneo, orang-utans were observed to build nests, use overhead covers, break, wave, drop and throw branches and vegetation, and also to manipulate twigs and branches in play. In addition, Tanjung Puting orang-utans manipulated and crashed snags and wiped their faces with crumpled leaves (in agonistic displays and displacement activities). One adult female constructed a nest-like structure to bridge a narrow river and a wild adult male once was observed scratching himself with a stick broken from a dead branch. In contrast, ex-captive orang-utans released into the forest used tools in a variety of contexts. All tool-use commonly observed among wild orang-utans was observed among the ex-captives as well as hundreds of episodes of other kinds of spontaneous tool-use. Sticks were the most frequently used tools although other items, including human-made artifacts such as rags, spoons, cups, shovels, knives, hoes, rope, boats and rafts, were also utilized. Different learning experiences before maturity probably account for the differences in tool-using behavior exhibited by wild orang-utans and ex-captives. However, the superiority of ex-captive orang-utans in this regard is more apparent than real because wild orang-utans exhibit sophisticated manipulations of materials that, while technically not tool-use, nonetheless involve cognitive abilities of a high order. These sophisticated manipulations are primarily involved in locomotion and food-processing. Should selection pressures in the primary tropical rain forests ever gradually change, wild orang-utans probably could evolve complexes of tool-using behaviors equivalent to that exhibited by populations of wild chimpanzees.