Long-tailed macaques (Macaca fascicularis) are one of the most common monkeys in southeast Asia. Some populations along the shore are found to use stones as tools to crack oysters, bivalves and various kinds of shellfish. This tool-related foraging technique is extremely rare among primates. The tool use behaviors are found only in some populations of monkey species in the same location despite sharing environmental and ecological settings. There are also individual differences in populations that use tools, in which some monkeys customarily use a stone tool to access high-protein shellfish, while other members in the same group do not use stone tools at all.

Sketch and Fact contributed by Nalina Aiempichitkijkarn

Source: Malaivijitnond, S., Lekprayoon, C., Tandavanittj, N., Panha, S., Cheewatham, C. and Hamada, Y., 2007. Stone‐tool usage by Thai long‐tailed macaques (Macaca fascicularis). American Journal of Primatology: Official Journal of the American Society of Primatologists, 69(2), pp.227-233.