There Is More than One Way to Crack an Oyster: Identifying Variation in Burmese Long-Tailed Macaque (Macaca fascicularis aurea) Stone-Tool Use

Abstract

We explored variation in patterns of percussive stone-tool use on coastal foods by Burmese long-tailed macaques (Macaca fascicularis aurea) from two islands in Laem Son National Park, Ranong, Thailand. We catalogued variation into three hammering classes and 17 action patterns, after examining 638 tool-use bouts across 90 individuals. Hammering class was based on the stone surface used for striking food, being face, point, and edge hammering. Action patterns were discriminated by tool material, hand use, posture, and striking motion. Hammering class was analyzed for associations with material and behavioural elements of tool use. Action patterns were not, owing to insufficient instances of most patterns. We collected 3077 scan samples from 109 macaques on Piak Nam Yai Island’s coasts, to determine the proportion of individuals using each hammering class and action pattern. Point hammering was significantly more associated with sessile foods, smaller tools, faster striking rates, smoother recoil, unimanual use, and more varied striking direction, than were face and edge hammering, while both point and edge hammering were significantly more associated with precision gripping than face hammering. Edge hammering also showed distinct differences depending on whether such hammering was applied to sessile or unattached foods, resembling point hammering for sessile foods and face hammering for unattached foods. Point hammering and sessile edge hammering compared to prior descriptions of axe hammering, while face and unattached edge hammering compared to pound hammering. Analysis of scans showed that 80% of individuals used tools, each employing one to four different action patterns. The most common patterns were unimanual point hammering (58%), symmetrical-bimanual face hammering (47%) and unimanual face hammering (37%). Unimanual edge hammering was relatively frequent (13%), compared to the other thirteen rare action patterns (<5%). We compare our study to other stone-using primates, and discuss implications for further research.

On the neglected behavioural variation among neighbouring primate groups

“…In two populations of monkeys, more groups have been studied. Tan, Tan, Vyas, Malaivijitnond, and Gumert () found that five groups of Burmese long‐tailed macaques on the Piak Nam Yai Island, Thailand, exhibit group‐level differences in their use of stone tools to crack open oysters, in both material and behavioural elements of tool use. Perry et al () studied traditions in a total of 13 capuchin groups, but across four different study sites.…”

Analysis of sea almond (Terminalia catappa) cracking sites used by wild Burmese long‐tailed macaques (Macaca fascicularis aurea)

“…The use‐wear analysis of the stone tools demonstrated conclusively that macaque sea almond nut processing tools predominantly showed used wear on their broad faces, as past work has shown (Gumert et al, ). Nuts and motile shellfish are generally cracked on an anvil surface by striking down on the target with the face of the stone, which differs from axe hammers used to strike sessile oysters (Gumert et al, ; Haslam et al, ; Tan et al, ). These findings give indication of how the stones were used at the sites we collected from, and are consistent with how we expected them to be used.…”

“…This broad categorization is useful in identifying how macaque stone tools were used in the past (Haslam et al, , ). Recently, Tan, Tan, Vyas, Malaivijitnond, and Gumert () showed that macaque stone tools contains greater variation than previous indirect reports. These authors classified the stone tools used by macaques into three hammering classes based on the surface of the stone use: face, edge, or point.…”

“…These trees are mainly situated along the upper border of the intertidal zone, and they drop fruit along this zone. Unlike the continual availability of mollusks along the coasts (Gumert & Malaivijitnond, ; Tan et al, ), both in time and space, sea almonds are only available at their trees and during their fruit production. As a result, the availability of sea almonds to macaques is more limited than marine prey, and, therefore, less predictable.…”

Validation of a Noninvasive Hair Trapping Method for Extractive-Foraging Primates

“…The somatosensory intelligence of long-tailed macaques is exemplified by a subspecies, the Burmese long-tailed macaque (M. fascicularis aurea), that uses percussive stone tool technology to exploit shellfish on the coastlines of Thailand and Myanmar [Malaivijitnond et al, 2007;Gumert et al, 2009Gumert et al, , 2013. The behavior resembles the nut-cracking activities of capuchins, but macaques use stone tools on a greater diversity of food species [Gumert and Malaivijitnond, 2012] and use a wider variety of techniques and action patterns [Tan et al, 2015].…”