What would classic Ethologists do? Examining the source of nut-cracking with naïve, unenculturated orangutans (Pongo abelii & Pongo pygmaeus)

Abstract

Despite advances in the study of non-human animal tool behaviour, the sources of tool-use behaviours are still debated. Often, different social and individual learning variants are assumed to play a role in behaviour acquisition. However, without the use of experimental controls, it is impossible to pinpoint which type of learning is responsible for the behaviour in question. We argue that this issue should be addressed with recourse to experimental approaches rooted in classic ethology. Building on the pioneering work by the founders of Ethology (e.g., Nikolaas Tinberg and Konrad Lorenz), we suggest that baseline experiments must be carried out before conclusions can be drawn on the role of any type of learning mechanism in the acquisition of behaviours. For example, we carried out a baseline study on the mechanisms behind nut-cracking in orangutans. We tested 12 naïve, captive, unenculturated orangutans, across two testing institutions (Leipzig: Pongo abelii; Mage=20.3; age range=10-34; 4F; Zürich: 6 Pongo abelii and two Pongo pygmaeus; Mage=14; age range =2-30; 5F). The subjects were provided with the materials necessary for nut-cracking, and no demonstrations and/or training beforehand. Out of the twelve orangutans, at least four individuals, one from Leipzig and three from Zürich, spontaneously expressed nut-cracking with a wooden hammer in the baseline. These results suggest that the behavioural form of nut-cracking can emerge in orangutans through individual learning and non-copying social learning mechanisms.