An article published in the journal “PLOS ONE” reports the observation of the spontaneous use of tools to dig food buried in the ground in the zoo by a group of chimpanzees on the island where there’s the Kristiansand Zoo, in Norway. A team of researchers led by Adriana Hernandez-Aguilar of the University of Oslo observed the kind of actions taken by chimpanzees that never had the chance to observe them.
Various types of use of instruments have been observed in wild chimpanzees, in 1995 an article published in the journal “Journal of Anthropological Research” reported the use of tools to dig food buried in specimens of the species tufted capuchin (Sapajus apella) and in 2004 an article published in the journal “Science” reported that type of behavior in specimens of the species bearded capuchin (Sapajus libidinosus).
In some cases, the use of tools to access food in the soil such as roots or tubers, the so-called plant underground storage organs (USOs), by chimpanzees has been reported but these are anecdotes while in various species of monkeys food excavations with bare hands have been observed. That’s an interesting type of research because that type of use of tools could have played a role in the adaptations of hominins during their evolution. For this reason researchers need to report documented observations that can be discussed in a rigorous way.
Adriana Hernandez-Aguilar’s team observed the behavior of ten chimpanzees of the species Pan troglogytes of which eight were born in captivity and no one had the chance to observe excavation activity. The researchers dug five small holes in which they left fruit, leaving them initially open to allow the chimpanzees to notice the contents and also leaving various branches and sticks that could be used as tools. In subsequent tests the fruit was covered and no potential tools were left.
The result was that nine of the ten chimpanzees successfully excavated buried fruit at least once and eight of them used tools instead of digging with their bare hands. In the tests where there were no branches and sticks near the holes they went to look for some using the local vegetation. During the tests they reused some tools, preferring long ones. On various occasions they took turns to excavate, sharing the recovered fruit. The image (Courtesy Motes-Rodrigo et al) shows various ways of using tools in the excavation phases: to probe (A), perforate (B), pount (C), dig (D), shovel (E) and enlarge (F).
The researchers discuss the possible influence of the state of captivity on the chimpanzees behavior, which for example lead to greater contacts among individuals and the lack of predators. Several social behaviors have been observed with the possibility of learning from the example of other individuals. This also requires caution in comparing these behaviors with those of wild populations.
The researchers also warn that today’s apes shouldn’t be considered equal to the ancient hominins despite the possible behavior similarities. The assessments are made difficult also because stone tools have been discovered dating back to periods of australopithecines but wooden tools can’t preserve for such long times. Nevertheless, any observation of primate skills in using tools can offer clues to the history of human ancestors.
