Macaques crack shellfish in coastal environments with specialized stone-hammering techniques. I provide the first examination of skill development from 866 object-manipulation and 7,400 tool-use bouts, collected over 15 months, using longitudinal analyses of infants' object manipulation (N = 7) and cross-sectional comparisons of manipulative and tool-use behavior (N = 69). I adopt a Perception-action approach, examining how the emergence of actions on objects relate to the spatial-relational and percussive challenges of tool use. Infants begin manipulating single items, particularly stones, at 1-2 months. Combining objects predominates (78%) by 1.5-2.5 years, and bouts involving food and tools but with incorrect spatial relations and action sequences prevail (73%) by 2.5-3.5 years. Placing, precedes rubbing objects on surfaces. Percussion emerges last, as disorganized striking before becoming consistent and targeted. Macaques manipulate combinations of stones and oysters, before stones, anvils, and motile shellfish, but success on either food type is only observed at 2.5-3.5 years. After competence, success rates and strike accuracy improve within 3 months on oysters and 5 months on motile shellfish. Older tool users (>4.5 years) had higher success rates, strike accuracy, strike efficiency, and tool fidelity. Macaque tool-use appears facilitated by a propensity for stone manipulation, but challenged by mastering spatial relations and percussion. I relate my findings to the development of stone-tool use in capuchins and chimpanzees, stone-handling in related macaque species, object play in Old World monkeys, and percussion in children, to further understand how biological propensities, environments, and social influences contribute to perception-action learning across species. (PsycINFO Database Record

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.

Since its inception, archaeology has traditionally focused exclusively on humans and our direct ancestors. However, recent years have seen archaeological techniques applied to material evidence left behind by non-human animals. Here, we review advances made by the most prominent field investigating past non-human tool use: primate archaeology. This field combines survey of wild primate activity areas with ethological observations, excavations and analyses that allow the reconstruction of past primate behaviour. Because the order Primates includes humans, new insights into the behavioural evolution of apes and monkeys also can be used to better interrogate the record of early tool use in our own, hominin, lineage. This work has recently doubled the set of primate lineages with an excavated archaeological record, adding Old World macaques and New World capuchin monkeys to chimpanzees and humans, and it has shown that tool selection and transport, and discrete site formation, are universal among wild stone-tool-using primates. It has also revealed that wild capuchins regularly break stone tools in a way that can make them difficult to distinguish from simple early hominin tools. Ultimately, this research opens up opportunities for the development of a broader animal archaeology, marking the end of archaeology's anthropocentric era.

Stone-hammering behaviour customarily occurs in Burmese long-tailed macaques, Macaca fascicularis aurea, and in some Burmese-common longtail hybrids, M. f. aurea × M. f. fascicularis; however, it is not observed in common longtails. Facial pelage discriminates these subspecies, and hybrids express variable patterns. It was tested if stone hammering related to facial pelage in 48 hybrid longtails, across two phenotypes — hybrid-like () and common-like (). In both phenotypes, tool users showed similar frequency and proficiency of stone hammering; however, common-like phenotypes showed significantly fewer tool users (42%) than hybrid-like phenotypes (76%). 111 Burmese longtails showed the highest prevalence of tool users (88%). Hybrid longtails living together in a shared social and ecological environment showed a significant difference in tool user prevalence based on facial pelage phenotype. This is consistent with inherited factors accounting for the difference, and thus could indicate Burmese longtails carry developmental biases for their tool behaviour.