Technological Response of Wild Macaques (Macaca fascicularis) to Anthropogenic Change

Anthropogenic disturbances have a detrimental impact on the natural world; the vast expansion of palm oil monocultures is one of the most significant agricultural influences. Primates worldwide consequently have been affected by the loss of their natural ecosystems. Long-tailed macaques (Macaca fascilularis) in Southern Thailand have, however, learned to exploit oil palm nuts using stone tools. Using camera traps, we captured the stone tool behavior of one macaque group in Ao Phang-Nga National Park. Line transects placed throughout an abandoned oil palm plantation confirmed a high abundance of nut cracking sites. Long-tailed macaques previously have been observed using stone tools to harvest shellfish along the coasts of Thailand and Myanmar. The novel nut processing behavior indicates the successful transfer of existing lithic technology to a new food source. Such behavioral plasticity has been suggested to underlie cultural behavior in animals, suggesting that long-tailed macaques have potential to exhibit cultural tendencies. The use of tools to process oil palm nuts across multiple primate species allows direct comparisons between stone tool using nonhuman primates living in anthropogenic environments

Analysis of wild macaque stone tools used to crack oil palm nuts

The discovery of oil palm (Elaeis guineensis) nut-cracking by wild long-tailed macaques (Macaca fascicularis) is significant for the study of non-human primate and hominin percussive behaviour. Up until now, only West African chimpanzees (Pan troglodytes verus) and modern human populations were known to use stone hammers to crack open this particular hard-shelled palm nut. The addition of non-habituated, wild macaques increases our comparative dataset of primate lithic percussive behaviour focused on this one plant species. Here, we present an initial description of hammerstones used by macaques to crack oil palm nuts, recovered from active nut-cracking locations on Yao Noi Island, Ao Phang Nga National Park, Thailand. We combine a techno-typological approach with microscopic and macroscopic use-wear analysis of percussive damage to characterize the percussive signature of macaque palm oil nut-cracking tools. These artefacts are characterized by a high degree of battering and crushing on most surfaces, which is visible at both macro and microscopic levels. The degree and extent of this damage is a consequence of a dynamic interplay between a number of factors, including anvil morphology and macaque percussive techniques. Beyond the behavioural importance of these artefacts, macaque nut-cracking represents a new target for primate archaeological investigations, and opens new opportunities for comparisons between tool using primate species and with early hominin percussive behaviour, for which nutcracking has been frequently inferred

Primate Archaeology Evolves

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

Artifact and Artifact Categorization: Comparing Humans and Capuchin Monkeys

International audienceWe aim to show that far-related primates like humans and the capuchin monkeys show interesting correspondences in terms of artifact characterization and categorization. We investigate this issue by using a philosophically-inspired definition of physical artifact which, developed for human artifacts, turns out to be applicable for cross-species comparison. In this approach an artifact is created when an entity is intentionally selected and some capacities attributed to it (often characterizing a purpose). Behavioral studies suggest that this notion of artifact is not specific to the human kind. On the basis of the results of a series of field observations and experiments on wild capuchin monkeys that routinely use stone hammers and anvils, we show that the notions of intentional selection and attributed capacity appear to be at play in capuchins as well. The study also suggests that functional criteria and contextualization play a fundamental role in terms of artifact recognition and categorization in nonhuman primates

Old World Monkeys Compare to Apes in the Primate Cognition Test Battery

Understanding the evolution of intelligence rests on comparative analyses of brain sizes as well as the assessment of cognitive skills of different species in relation to potential selective pressures such as environmental conditions and social organization. Because of the strong interest in human cognition, much previous work has focused on the comparison of the cognitive skills of human toddlers to those of our closest living relatives, i.e. apes. Such analyses revealed that apes and children have relatively similar competencies in the physical domain, while human children excel in the socio-cognitive domain; in particular in terms of attention sharing, cooperation, and mental state attribution. To develop a full understanding of the evolutionary dynamics of primate intelligence, however, comparative data for monkeys are needed. We tested 18 Old World monkeys (long-tailed macaques and olive baboons) in the so-called Primate Cognition Test Battery (PCTB) (Herrmann et al. 2007, Science). Surprisingly, our tests revealed largely comparable results between Old World monkeys and the Great apes. Single comparisons showed that chimpanzees performed only better than the macaques in experiments on spatial understanding and tool use, but in none of the socio-cognitive tasks. These results question the clear-cut relationship between cognitive performance and brain size and – prima facie – support the view of an accelerated evolution of social intelligence in humans. One limitation, however, is that the initial experiments were devised to tap into human specific skills in the first place, thus potentially underestimating both true nonhuman primate competencies as well as species differences

Primate archaeology evolves

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

To Each According to His Need? Variability in the Responses to Inequity in Nonhuman Primates

While it is well established that humans respond to inequity, it remains unclear the extent to which this behavior occurs in our nonhuman primate relatives. By comparing a variety of species, spanning from New World and Old World monkeys to great apes, scientists can begin to answer questions about how the response to inequity evolved, what the function of this response is, and why and how different contexts shape it. In particular, research across nonhuman primate species suggests that the response is quite variable across species, contexts and individuals. In this paper, we aim to review these differences in an attempt to identify and better understand the patterns that emerge from the existing data with the goal of developing directions for future research. To begin, we address the importance of considering socio-ecological factors in nonhuman primates in order to better understand and predict expected patterns of cooperation and aversion to inequity in different species, following which we provide a detailed analysis of the patterns uncovered by these comparisons. Ultimately, we use this synthesis to propose new ideas for research to better understand this response and, hence, the evolution of our own responses to inequity

Male Mating Tactics in Captive Rhesus Macaques (Macaca mulatta): The Influence of Dominance, Markets, and Relationship Quality

Male mating success in a multimale–multifemale group can depend on several variables: body condition, dominance, coalitions, “friendship,” or an exchange of services for mating access. Exchange patterns may also be determined by market effects or social relationships. We studied the mating tactics of males in a captive, multimale–multifemale group of rhesus macaques and the resulting patterns of mating and paternity to determine the influence of dominance rank, mating markets, and relationship quality on their mating tactics. Male rank was positively related to the total number of copulations and the number of mating partners, but did not explain male mating distribution completely. Moreover, male fertilization success was not related to male rank. Males did not exchange grooming for mating access on the same day and neither the supply nor the rank (as a proxy for quality) of receptive females affected the amount of male grooming, suggesting that market effects did not explain male mating access. However, there was a positive correlation between long-term grooming patterns of both males and females and mating access, indicating that social relationships were important for male mating access. Paternity data revealed that these social relationships were also important for male reproductive success. We conclude that both male rank and male–female “friendship” determined male mating access in these rhesus macaques, but that “friendship” was more important in determining paternity, emphasizing the importance of intersex social bonds in male mating success in multimale primate societies

Sexual Signalling in Propithecus verreauxi: Male “Chest Badge” and Female Mate Choice

Communication, an essential prerequisite for sociality, involves the transmission of signals. A signal can be defined as any action or trait produced by one animal, the sender, that produces a change in the behaviour of another animal, the receiver. Secondary sexual signals are often used for mate choice because they may inform on a potential partner's quality. Verreaux's sifaka (Propithecus verreauxi) is characterized by the presence of two different morphs of males (bimorphism), which can show either a stained or clean chest. The chest becomes stained by secretions of the sternal gland during throat marking (rubbing throat and chest on a vertical substrate while smearing the scent deposition). The role of the chest staining in guiding female mate choice was previously hypothesized but never demonstrated probably due to the difficulty of observing sifaka copulations in the wild. Here we report that stained-chested males had a higher throat marking activity than clean-chested males during the mating season, but not during the birth season. We found that females copulated more frequently with stained-chested males than the clean-chested males. Finally, in agreement with the biological market theory, we found that clean-chested males, with a lower scent-releasing potential, offered more grooming to females. This “grooming for sex” tactic was not completely unsuccessful; in fact, half of the clean-chested males copulated with females, even though at low frequency. In conclusion, the chest stain, possibly correlated with different cues targeted by females, could be one of the parameters which help females in selecting mates