Leaf-tool use for drinking water by wild chimpanzees (Pan troglodytes): acquisition patterns and handedness.

Chimpanzees (Pan troglodytes) are known to make and use a variety of tools, activities which require them to employ their hands in a skilful manner. The learning process underlying the acquisition of tool-using skills, and the degree of laterality evident in both immature and mature performers are investigated here focusing on the use of leaves for drinking water by members of the Bossou chimpanzee community in Guinea, West Africa. In addition, comparisons are drawn between the present findings and our previous data on the cracking of oil-palm nuts (Elaeis guineensis) using stone tools by members of the same community. The use of leaves for drinking water emerges approximately 2 years earlier than nut cracking, at around the age of 1.5 years, although the manufacture of leaf tools begins only at 3.5 years of age. In addition, in clear contrast with nut cracking, the majority of chimpanzees are ambidextrous in their use of leaves, with only certain individuals showing a bias for one hand. We discuss possible explanations for the earlier emergence and increased ambidextrousness that characterises leaf-tool use in comparison with other forms of tool use by wild chimpanzees. In summary, our results provide the first detailed description of the acquisition process underlying leaf-tool use along with the accompanying patterns of handedness, while also being the first to provide comparisons of the development of different forms of tool use within the same wild chimpanzee population.