LAUSR

Nut‐cracking with hammer tools (henceforth: nut‐cracking) has been argued to be one of the most complex tool‐use behaviors observed in nonhuman animals. So far, only chimpanzees, capuchins, and macaques have been observed using tools to crack nuts in the wild (Boesch and Boesch, 1990; Gumert et al., 2009; Mannu and Ottoni, 2009). However, the learning mechanisms behind this behavior, and the extent of nut‐cracking in other primate species are still unknown. The aim of this study was two‐fold. First, we investigated whether another great ape species would develop nut‐cracking when provided with all the tools and appropriate conditions to do so. Second, we examined the mechanisms behind the emergence of nut‐cracking by testing a naïve sample. Orangutans (Pongo abelii and Pongo pygmaeus) have the second most extensive tool‐use repertoire among the great apes (after chimpanzees) and show flexible problem‐solving capacities. Orangutans have not been observed cracking nuts in the wild, however, perhaps because their arboreal habits provide limited opportunities for nut‐cracking. Therefore, orangutans are a valid candidate species for the investigation of the development of this behavior. Four nut‐cracking‐naïve orangutans at Leipzig zoo (P. abelii; Mage = 16; age range = 10–19; 4F; at the time of testing) were provided with nuts and hammers but were not demonstrated the nut‐cracking behavioral form. Additionally, we report data from a previously unpublished study by one of the authors (Martina Funk) with eight orangutans housed at Zürich zoo (six P. abelii and two P. pygmaeus; Mage = 14; age range = 2–30; 5F; at the time of testing) that followed a similar testing paradigm. Out of the twelve orangutans tested, at least four individuals, one from Leipzig (P. abelii) and three from Zürich (P. abelii and P. pygmaeus), spontaneously expressed nut‐cracking using wooden hammers. These results demonstrate that nut‐cracking can emerge in orangutans through individual learning and certain types of non‐copying social learning.