Abstract # 92:

Scheduled for Friday, June 18, 2010 07:00 PM-09:00 PM: Session 18 (Medallion Ballroom C/D/E/F) Poster Presentation


WILD BEARDED CAPUCHIN MONKEYS (PIAUI, BRAZIL) POSITION NUTS SYSTEMATICALLY INTO PITS ON ANVILS BEFORE STRIKING THE NUTS WITH STONE TOOLS

D. Fragaszy1, A. M. Allen1 and B. Wright2
1University of Georgia, Department of Psychology, Athens, Georgia 30602, USA, 2Kansas City University of Medicine and BioSciences
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Using a tool is considered cognitively challenging because it involves planning actions and producing spatial relationships among objects and surfaces. Bearded capuchin monkeys (Cebus libidinosus) crack nuts on anvils using stones as hammers. Our team showed that these monkeys select hammer stones by weight and composition and nuts by resistance to cracking. Here we report on a third component of the nut-cracking cycle: placement of the nut onto the anvil prior to striking it. We noticed that the monkeys repetitively move the ellipsoid nuts in pits on the anvils before striking them. We tested whether the monkeys systematically place the nuts in a particular orientation, rather than randomly. We marked 121 nuts (Piaçava; Orbignya) with distinctive colors along two equidistant meridians along the long axis. One meridian ran through the flattest surface, determined by rolling the nut on a flat surface. We opportunistically videotaped 8 monkeys as they each positioned these nuts >10 times at a familiar anvil. In playback we coded the position of the nut on the anvil prior to each strike for identified monkeys. Monkeys positioned the “flat” meridian into the pit on 82% of position events [individual range 71–94%], a non-random outcome [individual X2=9.31 to 36.26(df=1), all P<0.05]. Perhaps this strategy affects efficiency of cracking or the probability of displacing the nut.