It was once believed that tool use was one of the signifying traits distinguishing humans from the rest of the animal world, but research has shown that is simply not the case. Chimps crack nuts, gorillas build rudimentary bridges, and dolphins use sponges to stir up the ocean floor, just to name a few. Scientists can now add macaques to the list, for it turns out they are quite handy with a hammer.
In a study released today in the journal Plos One, researchers from the Nanyang Technological University in Singapore conducted an 8-year field project in which they observed Burmese long-tailed macaques on the islands of Piak Nam Yai and Thao in Laem Son National Park, Thailand. Their goal was to catalogue tool production and usage among the macaques, and as their study shows, their toil was well-rewarded.
It has already been documented that macaques use tools to crack open various types of food, the majority of which are oysters and snails. It has also been deduced that they employ two basic hammering forms to break open their prey: axe hammering, which employs a sharper rock, and is used primarily on oysters, and pound hammering, where a large stone is used in conjunction with an anvil on which they crush other types of crustaceans. By developing more detailed categories of tool use that employ not only the type of tool but the associated action pattern, the team hoped to better understand macaque tool usage and facilitate future studies among primates.
The researchers first catalogued the parts of the tools used in hammering: the flat face of the rock, its narrow edge, or its point. Their next step was to categorize the action patterns the macaques employed during hammering. They observed hand use, posture, and striking motion among 90 macaques in over 600 tool-use events. Once the categories were identified, they then set out to determine the distribution of macaques within each category.
What they found was that 80% of the macaques used stone tools, which supported previous findings, and that they relied on three hammering classes based on whether the tool's face, edge, or point was used. They were also able to identify 17 different types of action patterns employed within the hammering classes, the most prevalent being single-handed point hammering, and that each individual used between one and four different types of action patterns to extract their prey.
The team was also curious how these action patterns varied among different groups of macaques. They discovered that tools and techniques varied based on available foods. Along the coasts, where oysters were predominant, face hammering prevailed, whereas in the mangrove forests, point pounding was the chosen technique, which suggests that behavior patterns among the macaques are influenced by the habitats in which they live.
Now that they have systematically identified categories of variation in stone tool use among the macaques at Laem Son National Park, the researchers hope their data can be used for broader comparative studies among other primates. And a better understanding of tool use among primates helps elucidate the evolution of tools within our own family tree.