Eighty percent of a population of Burmese long-tailed macaques on an island in southern Thailand use stone and shell tools to crack open seafood, and do so using 17 different action patterns, according to a study published May 13, 2015 in the open-access journal PLOS ONE by Amanda Tan from Nanyang Technological University, Singapore, and colleagues, under an 8 year field project led by Michael D Gumert, also from NTU.
The authors of the study explored variation in how Burmese long-tailed macaques used percussive stone and shell tools to hammer coastal foods on Piak Nam Yai and Thao Islands in Laem Son National Park, Thailand. First, they catalogued the parts tool that macaques used for hammering: the flat face, narrow edge, or point. Next, they categorized the action patterns the macaques used during the hammering, including hand use, posture, and striking motion, for over 600 tool-uses across 90 individuals. Once the tool use and action patterns were identified, they observed over 100 macaques in over 3000 time points on Piak Nam Yai Island's coasts, to determine the proportion of individuals using each tool and action pattern.
Analysis of the observation showed that 80% of macaques used tools, supporting past findings from the project, each employing one to four different action patterns, and a total of 17 different action patterns in the population. Most commonly, the macaques used one-handed hammering with the points of smaller tools to crack open sessile rock oysters that required precision striking, and used one- or two-handed hammering with the faces and edges of larger tools to crack unattached shellfish that had to first be placed on anvils, reflecting different techniques for different foods.
The authors suggest that cataloguing the tools and actions involved in macaque tool use lays the foundation for future studies, such as understanding how macaque tool use develops, and comparing macaque tool use with that of other stone-tool-users in the primate lineage.
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Citation: Tan A, Tan SH, Vyas D, Malaivijitnond S, Gumert MD (2015) There Is More than One Way to Crack an Oyster: Identifying Variation in Burmese Long-Tailed Macaque (Macaca fascicularis aurea) Stone-Tool Use. PLoS ONE 10(5): e0124733. doi:10.1371/journal.pone.0124733
Funding: This research was supported by the Thailand Research Fund (Grant RSA/G2/2545 and RMU 4880019), The Center for Excellence in Biodiversity at Chulalongkorn University, the Ratchadapisek Sompoch Endowment Fund (2013), Chulalongkorn University (Sci-Super 2014-021), the Ministry of Education (Singapore), Academic Research Fund (Grant RG07/95), the College of Humanities, Arts, and Social Sciences (CoHASS) Incentive Grant, School of Humanities and Social Sciences, Nanyang Technological University, and a research grant for doctoral students from The Leakey Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.