Macaques’ stone tool use varies despite same environment

Stone tool use develops differently within species of Old World monkeys in spite of shared environmental and ecological settings, according to a new study involving UCL. Macaques are the only Old World monkeys that have been observed using percussive stone tools and scientists do not know for certain how or why certain groups have developed this behaviour. In the study, published in eLife journal, researchers analysed data on wild long-tailed macaques living in two islands (Boi Yai Island and Lobi Bay) about 15 kilometres apart in southern Thailand, within the Ao Phang Nga National Park. The researchers assessed 115 stone tools combined from both locations. They found that despite living in the same environment, with access to the same stone tool making resources (with limestone constituting the most available raw material) and the same prey species, that wild long-tailed macaques on Boi Yai Island selected heavier tools than those on Lobi Bay. In addition, the stone tools on Boi Yai Island showed a greater number of wear patterns, indicating that the tools are being used multiple times and on more than one prey species. In particular, they found that stone tools used to crack open oysters are larger and more intensively used on Boi Yai Island compared to Lobi Bay.