New research from the University of Tübingen demonstrates that nut-cracking can emerge in Sumatran (Pongo abelii) and Bornean (Pongo pygmaeus) orangutans through individual learning and certain types of non-copying social learning.
Padana, a female orangutan at Leipzig Zoo, continued to use wooden hammers to crack nuts for some time after the end of the study. Image credit: Claudio Tennie.
“Nut-cracking with hammer tools has been argued to be one of the most complex tool-use behaviors observed in nonhuman animals,” said study lead author Dr. Elisa Bandini from the Department for Early Prehistory and Quaternary Ecology at the University of Tübingen and colleagues.
“So far, only chimpanzees, capuchins, and macaques have been observed using tools to crack nuts in the wild.”
“However, the learning mechanisms behind this behavior, and the extent of nut-cracking in other primate species are still unknown.”
To test the extent of this behavior in great apes and the learning mechanisms underlying it, the researchers provided 12 naïve orangutans across two testing institutions — Leipzig and Zürich zoos — with hammer tools and shelled nuts.
At least four of the animals spontaneously cracked nuts with the hammer tools, demonstrating a similar behavior to wild primate nut-cracking.
“One orangutan initially used the anvil as a hammer,” the scientists said.
“In later experiments, the anvil was fixed to the ground, whereupon the animal spontaneously used the wooden hammer to crack the nuts.”
“The other three older orangutans, however, tried using their hands or teeth.”
The findings suggest that individual learning is the main driver for the acquisition of nut-cracking in orangutans, alongside several factors including non-copying social learning, general genetic predispositions, and cognitive capacities that allow for finding solutions to problems in a flexible way.
“So the orangutans themselves can develop this complex behavior purely through individual learning,” Dr. Bandini said.
“Nut-cracking with tools is thus — at least in orangutans — a behavior that does not require cultural transmission, it does not require models.”
The results were published in the American Journal of Primatology.
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Elisa Bandini et al. 2021. Naïve orangutans (Pongo abelii and Pongo pygmaeus) individually acquire nut-cracking using hammer tools. American Journal of Primatology 83 (9): e23304; doi: 10.1002/ajp.23304
