AsianScientist (May 20, 2015) – 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 in PLOS ONE. The research was led by Ms. Amanda Tan from Nanyang Technological University, under an eight year field project led by Assistant Professor Michael D Gumert.
The authors of the study explored variations 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 of the 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 3,000 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 percent 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 cataloging 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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