Abstract # 154:

Scheduled for Sunday, September 20, 2009 06:30 PM-09:00 PM: Session 14 (Mission Bay Ballroom CDE) Poster Presentation


CAREFUL SELECTION OF NUTS AND STONES FOR EFFICIENT CRACKING BY WILD CAPUCHIN MONKEYS

R. Greenberg1, D. Fragaszy1, Q. Liu1, E. Visalberghi2, E. Ottoni3 and P. Izar3
1University of Georgia, Psychology Department , Athens, GA 30602, USA, 2ISTC, CNR (Italy), 3Universidade de Sao Paulo
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Wild bearded capuchin monkeys (Cebus libidinosus) use stone tools to crack open tough palm nuts to ingest the kernel. We conducted a series of field experiments with a group of wild bearded capuchins in Piauí, Brazil to evaluate their choice of two nuts differing in resistance (Attalea and Astrocaryum) and of two manufactured stones of equal volume but different masses. We coded choice of nut and stone and actions with the nuts from videotapes. Each monkey [n=8] selected the nut that was easier to crack [all Χ²(1)>6.50, p<0.05], and when cracking the most resistant kind of nut (Attalea), each monkey [n=4] consistently selected the heavier stone when the stones differed in weight by at least 500 grams [all Χ²(1)>4.50, p<0.05]. When the stones differed by 213 – 286 gm (611 vs 824, or 824 vs 1110), four of six monkeys exhibited a significant preference for the heavier stone [per individual, all Χ²(1)>4.50, p<0.05]. This study shows that capuchin monkeys are sensitive to properties of nuts and stones, and that they can discriminate between stones differing in weight by as little as 213 gm. The findings suggest that the monkeys carefully select stones and nuts to maximize the reliability of payoff.