Abstract # 185:

Scheduled for Sunday, September 18, 2011 07:00 PM-09:00 PM: Session 23 (Salon G (Sixth Floor)) Poster Presentation


L. Massaro1,3, Q. Liu2, E. Visalberghi1 and D. Fragaszy2
1Consiglio Nazionale delle Ricerche, Istituto di Scienze e Tecnologie della Cognizione, Rome, USA, 2University of Georgia, 3Sapienza University of Rome
     Optimization theories predict that animals act to maximize benefits and minimize costs of behavior. Wild bearded capuchins transport stones to anvils and use them to crack nuts. Transport is increasingly effortful with distance and with greater stone mass but greater stone mass reduces the number of strikes needed to crack a nut. We carried out two experiments with wild capuchins (n=5) to explore the monkeys’ choice of stones when mass and distance to the anvil varied. In Experiment 1 two stones of the same mass were positioned at two distances from the anvil. All subjects significantly preferred the closer stone (Binomial Test, p’s <0.05). In Experiment 2 we positioned two stones (0.9 and 1.9 kg, both heavy enough to open the nuts) at 3 and 6 m from the anvil, alternating the position of the heavy stone. In this experiment, if monkeys prefer to minimize the cost of transport, they should transport the closer stone. Alternatively, if monkeys prefer to minimize the number of strikes, they should transport the heavier stone. Four out of five monkeys significantly preferred the closer stone (Binomial Test, p’s<0.05); one preferred the heavier stone (Binomial Test, p<0.05). Bearded capuchin monkeys select between suitable stone tools primarily to minimize transport distance, not to maximize mass of the stone. Supported by a grant from the LSB Leakey Foundation.