The formation of the brush-sticks: modification of chimpanzees or the by-product of folding?
Based on field research and experimental treatments of trees, we investigated the formation of the brush-like shape of digging sticks used by chimpanzees (Pan troglodytes troglodytes). Evidence obtained in the field consisted of digging sticks found in Mboete, Equatorial Guinea, which is a newly reported locality for this type of tool, and Campo, Cameroon. Digging sticks used by chimpanzees in these areas had a brush-like shape at one end, which was quite different from the other end that was probably used for digging. In our tree-breaking experiment, 8 out of 17 species acquired a typical brush-like shape without human modification when broken off, and the shapes of the stumps were similar to those found in the field. Other species did not acquire the brush-like shape naturally or even after human modifications, and the stumps had different shapes from those found in the field. Our findings suggest that the brush-like shapes of digging sticks are often naturally formed when broken off from trees, depending on the nature of the fibre structure, and that the brush-like end is not used as the digging tool. We conclude that the vegetation surrounding termite mounds might influence how chimpanzees combine different types of tools, i.e., digging stick, brush-stick and fishing tool, for obtaining termites.
Takemoto
Hiroyuki
H
Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan. takemoto@pri.kyoto-u.ac.jp
Hirata
Satoshi
S
Sugiyama
Yukimaru
Y
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D016703:Equatorial Guinea; D005247:Feeding Behavior / Q000502:physiology*; D002679:Pan troglodytes / Q000502:physiology*; D018547:Plant Stems / Q000033:anatomy & histology; D014197:Trees / Q000033:anatomy & histology*