When and where to practice: social influences on the development of nut-cracking in bearded capuchins (Sapajus libidinosus)

Abstract

The habitual use of tools by wild capuchin monkeys presents a unique opportunity to study the maintenance and transmission of traditions. Young capuchins spend several years interacting with nuts before cracking them efficiently with stone tools. Using a two-observer method, we quantified the magnitude of the social influences that sustain this long period of practice. During five collection periods (over 26 months), one observer recorded the behavior of 16 immature monkeys, and another observer concurrently recorded behavior of group members in the focal monkey's vicinity. The two-observer method provides a means to quantify distinct social influences. Data show that immatures match the behavior of the adults in time and especially in space. The rate of manipulation of nuts by the immatures quadrupled when others in the group cracked and ate nuts, and immatures were ten times more likely to handle nuts and 40 times more likely to strike a nut with a stone when they themselves were near the anvils. Moreover, immature monkeys were three times more likely to be near an anvil when others were cracking. We suggest a model for social influence on nut-cracking development, based on two related processes: (1) social facilitation from observing group members engaged in nut-cracking, and (2) opportunity for practice provided by the anvils, hammer stones and nut shells available on and around the anvils. Nut-cracking activities by others support learning by drawing immatures to the anvils, where extended practice can take place, and by providing materials for practice at these places.

Factors affecting cashew processing by wild bearded capuchin monkeys (Sapajus libidinosus, Kerr 1792)

“…Proximity to and interest toward skilled individuals by others during foraging are common in many species of birds and mammals [e.g., meerkats, Hoppitt et al, ] and much effort has been devoted to evaluating the contribution of observing proficient others foraging on the development of foraging skills by the youngsters [Hoppitt and Laland, ]. Young capuchin monkeys are usually very interested in adults’ processing activities with palm nuts [Coelho et al, ; Eshchar et al, in press; Ottoni et al, ] and other difficult foods, such as Sloanea fruits [O'Malley and Fedigan, ,] and beetle larvae in bamboo canes [Gunst et al, ]. Finally, young‐white faced capuchins ( C. capucinus ) show interest toward group members foraging on food items that are rare, difficult to process, or large [Perry and Jiménez, ].…”

“…The processing techniques used to exploit cashews in FBV are excellent candidates for social influences. Although data collection in the present study was not specifically designed to investigate this topic, as has been done for stone tool use in bearded capuchin monkeys [Eshchar et al, in press; Fragaszy et al, ], our method allows us to assess whether youngsters pay more attention to more proficient individuals than to less proficient ones.…”

Maternal influence on the development of nut‐cracking skills in the chimpanzees of the Taï forest, Côte d'Ivoire (Pan troglodytes verus)

“…In the specific case of nut‐cracking, studies conducted on two species of primates that engage in this behavior, chimpanzees (Biro et al, ; Inoue‐Nakamura & Matsuzawa, ) and capuchins ( Sapajus spp. ; Coelho et al, ; Eshchar, Izar, Visalberghi, Resende, & Fragaszy, ; Ottoni, Resende, & Izar, ), suggested that immature individuals acquire this behavior via different social learning processes, including local‐ and stimulus‐ enhancement, emulation, and social facilitation. A key condition for such learning to occur is a high level of tolerance that skilled individuals show towards unskilled individuals.…”

Synchronized practice helps bearded capuchin monkeys learn to extend attention while learning a tradition

“…In one recent study, while other group members were cracking and eating nuts, monkeys 6 y of age or younger were threefold more likely to be near an anvil, quadrupled their rate of interaction with nuts, and doubled their rate of percussing and striking compared with times when no monkey in the group was cracking nuts. Interactions with objects other than nuts showed the opposite pattern (48).…”

“…These monkeys start to interact with nuts and stones in the first year of life. They handle nuts, percuss nuts directly against a hard surface (hereafter, percuss), and strike nuts or nut shells with stones (hereafter, strike) for several years before they are able to crack palm nuts themselves (47,48). Thus, young monkeys exhibit remarkable persistence in a foraging activity that they cannot perform effectively.…”