Abstract # 2514 Poster # 41:

Scheduled for Saturday, September 19, 2009 06:30 PM-09:00 PM: Session 5 (Mission Bay Ballroom CDE) Poster Presentation


PROFICIENCY OF NUT-CRACKING IN WILD BEARDED CAPUCHIN MONKEYS (CEBUS LIBIDINOSUS)

T. Pickering1, D. Fragaszy1, Q. Liu1, E. Visalberghi2, E. Ottoni3 and P. Izar3
1University of Georgia, Department of Psychology, Athens, GA 30605, USA, 2Institute of Science and Technology of Cognition, CNR, Italy , 3Universidade de Sao Paulo
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Wild bearded capuchin monkeys crack tough palm nuts using stones and anvils. We evaluated the extent to which a monkey’s proficiency at cracking nuts reflects its mass and its behavior. We provided wild monkeys [N=11] and one human participant (Homo sapien) with palm nuts (Attalea spp.) and a single hammer stone (1.465 kg), at an anvil with flat and pitted surfaces. From video we scored actions and outcomes of each cracking episode. We recorded the monkeys’ weight as they voluntary stood on a scale. The most proficient monkey opened on average 15 nuts per 100 strikes; the least proficient, just over 1 nut per 100 strikes, and some monkeys cracked only pieces of already-cracked nuts. The monkeys’ body mass correlated strongly with proficiency [r(9)=0.75, p<0.01]. All the monkeys consistently placed whole nuts into a pit in the anvil surface before striking [mean=96% of strikes]. For the human, placing the nut into the pit rather than on the flat surface reduced the probability that the nut would fall off the anvil after it was struck [Χ²(1)=39.03, p<0.05]. Proficiency at cracking reflects acquired skill as well as body mass. Supported by NSF grant #BCS0352035, the National Geographic Society, and the University of Georgia.