Abstract # 187:

Scheduled for Monday, September 21, 2009 09:00 AM-09:10 AM: Session 17 (Shell Room) Oral Presentation


M. D. Gumert1, M. Kluck2 and S. Malaivijitnond2
1Nanyang Technological University, Division of Psychology, School of Humanities and Social Sciences, Singapore 639798, Singapore, 2Primate Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand

Long-tailed macaques in the Andaman sea region along the coast of Myanmar and Thailand (Macaca fascicularis aurea) use stone tools to crack open shellfish and nuts. At Laemson National Park in Thailand, we found evidence of oyster cracking at 3 islands, Koh Piak Nam Yai, Koh Thao, and Koh Phayam, and at one mainland sight located in Ranong. We have studied macaque stone tools at Koh Piak Nam Yai and found tools used to crack oysters attached to large rocks were smaller than hammers used to smash unattached food items (i.e., nuts and shellfish) on anvils [ANOVA, p<0.001; Tukey's HSD, p<0.05]. Moreover, tools used to crack oysters were more frequently scarred on the points, whereas tools used to pound food on anvils were more frequently scarred on the broad surfaces [ANOVA, p<0.01; Tukey's HSD, p<0.05]. Grip and usage variation were also found. Oyster tools were typically gripped with a precision pinch (i.e. thumb pressing tool into fingers) and passive palm support, while anvil tools were grasped with power grips (i.e., fingers actively pressing tool into palm). Macaques struck food items more rapidly when chipping oysters than when pounding food on anvils [t(58)=6.89, p<0.01] and at a wider range of orientation relative to the plane on which their body was situated [t(58)=5.04, p<0.01]. We distinguished two stone tool types. Axe hammers were lighter, and pounding hammers were larger, heavier stones. Moreover, axe hammers were used to finely chip attached oysters, whereas pounding hammers were used to strike downward on and crush unattached food items.