Obtaining raw material: plants as tool sources for Nigerian chimpanzees

Abstract

We investigated the acquisition of plant materials from which Nigerian chimpanzees manufacture wooden tools to harvest insects and honey from nests of army ants, honey bees and stingless bees. Slender trunks of juvenile trees and branches are most commonly used, and bendable vines rarely, probably reflecting the need to work with relatively sturdy tools to extract resources. While several tools are sometimes sourced from the same plant, there is also evidence for a depletion effect, as multiple tool sources at the same site are often spaced several metres apart. Identified tool sources belong to 27 species of at least 13 families. Honey-gathering implements are often chewed upon by chimpanzees. Interestingly, twigs of the most commonly used honey-gathering species possess antibacterial propensities and are favoured by Nigerians as chewing sticks. This suggests that extractive tools might possess associated medicinal or stimulatory properties. We do not know if chimpanzees actively select specific plant parts or species as we cannot compare observed with expected frequencies. Nevertheless, about three quarters of tools are picked from plants more than 6 m away from the extraction site, potentially indicating some degree of forward planning.