Primates

Chimpanzees, amongst other primates, are characterized by the large variability of habitats they can be found in as well as a large behavioral, sometimes cultural diversity. Such observations have launched a decades-long debate on the roots of behavioral diversity, stressing the need to document this behavioral variability in context, such as by connecting closely related populations through localized analyses. This study presents the first comprehensive description of feeding ecology from the Mwera South chimpanzee (Pan troglodytes schweinfurthii) community in the Bugoma Central Forest Reserve, in Uganda, establishing a valuable baseline for this previously unstudied population and providing a comparative perspective on the populations of Western Uganda and Eastern Democratic Republic of Congo. By employing multiple methodological approaches, including direct observation and fecal analysis, we describe dietary composition, seasonal patterns, and environmental influences on feeding behavior. Characterizing the feeding ecology of this previously unstudied population is critical for examining how ecological factors might influence how feeding patterns evolve depending on resource availability or chimpanzee behavior, in particular by favoring analyses at the regional level. In addition, we can better evaluate to what extent behavioral differences between chimpanzee communities stem from ecological constraints and/or cultural transmission pathways. Our findings suggest that the Bugoma chimpanzees seat at the location of a historic cultural junction, opening a large array of questions about historic movements and cultural diffusion in Eastern chimpanzees.

While it is well established that apes invent or individually learn new gestures, cases of development and use of novel gestures in monkeys are more rarely described. We report a case of a novel, idiosyncratic gesture in a Barbary macaque (Macaca sylvanus) at La Foret des Singes, Rocamadour, France. One adult male, Jomanix, was observed hand-clapping. To our knowledge, hand-clapping has never been described before in this species. To hand-clap, the male briefly shifted his weight onto his legs, lifted his upper body, and clapped both hands together. We recorded 30 instances of hand-clapping. Twenty-five of these hand-claps occurred in combination with other agonistic signals, such as lunges and open mouth threats. Recipients either responded with counter-aggression (N = 9) or a submissive response (N = 16). In five of the 30 events, the context was unclear. These observations suggest that the gesture constitutes an agonistic signal. According to the staff at La Foret des Singes, the hand-clapping may have been copied from staff members who occasionally hand-clap to shoo the animals away from areas where they were not supposed to be, but that notion remains speculative. In the meantime, another subject from the same group reportedly started to hand-clap, but the subject had passed away before we could document the behaviour. The observations show that Jomanix can flexibly combine a novel gesture with other established communicative signals. The hand-clap is goal-directed and fulfils the criteria for first-order intentional communication. This case, as well as anecdotal reports from a Tonkean macaque (Macaca tonkeana) hand-clapping to get attention, reveals greater flexibility in the gestural communication of this genus than previously assumed but also underscores that social learning of the production of communicative gestures occurs rarely in this taxon.

Quantitative acoustic analysis has been used to decipher individual differences, population structure, and taxonomic diversity in numerous primate species. We previously described three distinct call types in wild Aotus nigriceps, and now assess acoustic differences in two of these call types between social groups and spatially distinct populations. Acoustic parameters for both analyzed call types exhibited significant variability between groups. Similarly, geographically distant field sites were acoustically distinct from one another. Several groups also used a variation of a common call: a triplet Ch Ch instead of a duplicate. Other groups made use of ultrasonic frequencies which have not previously been reported in Aotus. Our results suggest that Aotus nigriceps exhibits substantial acoustic variability across sites that could potentially be useful for taxonomic classification, although additional geographically distant populations still need to be sampled. The possibility of individual signatures also exists and will require recording vocalizations from known individuals.

For nonhuman primates living in anthropogenic areas, predation by larger predators is relatively rare. However, smaller predators such as free-ranging as well as domesticated dogs can shape the socioecology of urban nonhuman primates, directly by attacking and predating upon them, or indirectly by modifying their activity patterns. Here, we describe 3 (2 potentially lethal) cases of dog attacks on adult rhesus macaques inhabiting an anthropogenic landscape in Northern India, and the circumstances surrounding these incidents. We discuss the importance of considering the presence of dogs while studying nonhuman primate populations across the anthropogenic gradient and its implications for understanding how human presence can directly and indirectly affect predator-prey relationship in these areas, as well as its potential role in modifying group social dynamics as well as in transmission of zoonotic agents.

The juvenile life stage is crucial in primates, yet the behavior and diet of juveniles is an understudied area of primatology. Compared with adults, considerably less is known about wild juvenile primate development, particularly that of western lowland gorillas (Gorilla gorilla gorilla). While sex differences in diet and time budgets are well studied in adults, work remains to be done on how age and sex influence juvenile behavior. Here, we use data from nine immature reintroduced western lowland gorillas to fill some of this knowledge gap. We found that the immature gorillas spent most time feeding, followed by resting. Younger juveniles spent less time resting than older individuals, instead spending more time in self-play compared with older juveniles and more time in locomotion than subadults. The group had a varied diet as would be expected for western lowland gorillas; predominantly eating stems, flowers/leaves and fruit, with subadults eating more stems compared to younger individuals. Sex was found to have little influence on either behavior or diet. Additionally, behavioral and dietary diversity were calculated in order to describe the diversity of immature western lowland gorilla behavior. There were no age or sex differences found among this group of individuals, suggesting behavioral repertoire and diet may be influenced by those in their social group. The wider aim of this study is to provide insights into immature western lowland gorilla behavior and diet in the wild while also contributing to understanding of the post-release period for rehabilitated primates.

Compositionality, a hallmark of human language, involves generating novel meaning by combining existing units. Nonhuman primates (mostly apes) are known to combine gestural units in non-random ways, but they do not make novel meaning with these combinations. What could, however, be the functional roles of these gesture sequences and whether they bear any significance to language evolution is still unclear. Moreover, studies on gesture-sequences in non-ape primate species is almost non-existent. Here, we investigated for the first time, the structure and functions of gesture sequences in the naturally occurring communication of wild bonnet macaques (Macaca radiata), using analyses akin to ape gesture studies (Genty & Byrne, 2010; Hobaiter & Byrne, 2011). Bonnet macaque gesture sequences exhibit non-random combinations of gestures and non-gesture units - certain gestures are significantly more common in sequences, they associate preferentially with specific other components and certain components are more likely to appear either at the beginning or at the end of a sequence. Interplay of these sequences form distinct gestural clusters, corresponding to affiliative/play and agonistic contexts. Although, the overall functions of bonnet macaque gesture sequences remain obscure, as in apes, we found that gesture sequences were specifically used as a persistence strategy, after the initial single gestures have failed to initiate and sustain social interactions. We discuss our findings in the light of a possibility that primate gesture sequences, coordinating the flow of social interactions, may be evolutionary precursors to pragmatic gestures in human language.

West African chimpanzees (Pan troglodytes verus) are critically endangered, therefore knowing their ecological needs is necessary to implement proper conservation measures, especially in the face of climatic change. We report here the consumption of soil by wild chimpanzees living in Comoe National Park, Ivory Coast. We confirmed through camera-trap recording that chimpanzees of all ages and both sexes consumed it for several years at least in one community and more occasionally in a second one, aided by leaf-sponge tools. Our results suggest that these chimpanzees living in a savanna-forest mosaic may need minerals supplement, including sodium or/and clay to aid digestion, mainly during the dry season.

The nut-cracking behaviour of the chimpanzees of Bossou Forest has been long documented and studied in order to understand ultimate drivers for this form of durophagy by these apes. At sites in which they break open the nuts of the oil palm (Elaeis guineaeensis) on stone anvils with stone hammers, fragments of the tools as well as remnants of the nuts may be deposited into local sediments; however, they may become less visible at the macroscopic level as these sites are no longer used (become dormant). We build upon work that has been done to document this unique cultural heritage in West African chimpanzees by interpreting phytolith assemblages in sediments at active nut-cracking sites (used within the last two months). We compare these assemblages with those found in sediments of sites that have been dormant for ~10 years and sites where chimpanzees have not been observed to access and crack open oil palm nuts with stone tools. We predicted that larger assemblages of spheroid echinates, a phytolith associated with palms, would be found at active nut-cracking sites, however we found no statistical difference between total spheroid echinates (measured as total number found per gram of dry sediment) assemblages produced across active nut-cracking, dormant, or non-nut-cracking sites. This may have been due to small sample size (N[≤]6 sediment samples for each of the three sites) and so further sample collection and analyses are needed for inter-site comparisons. We also measured 2D area (m2), perimeter and maximum diameter of spheroid echinates found in nut endocarps (shells) and leaflets from an oil palm frond. Intra-specific differences from all three measurements were found with these phytoliths being larger in the nut endocarp than the leaflet. This has implications for (re)interpreting the assemblages of spheroid echinate phytoliths at the three sites to determine if there is a greater productivity larger-sized spheroid echinates that fall within the size range of those measured for the nut endocarp (mean maximum diameter of 14.9 m versus 7.8 m for those found in oil palm leaflet). Finally, we argue for the importance of initialising and continuing the interpretation of phytolith assemblages in local sediments that are located near sites where directed plant input by non-human taxa has occurred, in this case, chimpanzees cracking open oil palm nuts using stone tools. This is important to refine our interpretation of phytolith assemblages where human and non-human taxa who use complex foraging strategies share ecological spaces.

AbstractObtaining genetic information from rare species is challenging for scientists, but it is crucial for understanding animal evolutionary history and informing conservation management initiatives. We present the first example of a collaborative local network that includes zoos and natural history collections to investigate the evolution, systematics, and conservation concerns of olingos (genus Bassaricyon, Procyonidae, Carnivora, Mammalia). We sequenced the entire (1,146 base pairs) cytochrome b gene to phylogenetically identify individuals that have been victims of wildlife trafficking. Unexpectedly, we detected an individual specimen belonging to Bassaricyon medius orinomus (western lowland olingo), which may represent a new geographical record for this taxon in Ecuador. Through our practical experiences, we describe how local collaboration is possible and crucial for promoting wildlife genetic research in the Global South and contributing to protecting the last populations of rare mammals. We also discuss the significance of wild animals under human care as a valuable genetic resource for scientific research, conservation strategies, and informed wildlife management decisions.

1.The objective of this study was to examine the impact of visitors on the behavior of chimpanzees at a sanctuary. We hypothesized there wouldnt be an increase in abnormal, agnostic, or self-directed behaviors during visits, nor a decrease in affiliative behaviors when visitors are present. The study examined the effects of visitor presence on chimpanzee behavior at Fundacio MONA, a rescue center. Key findings includeO_LINo significant changes in abnormal or self-directed behaviors or agonistic behaviors were observed with visitor presence. C_LIO_LIAffiliative behaviors (excluding grooming) showed a slight decrease during visits. C_LI These results indicate that guided visitor interactions do not adversely affect chimpanzee behavior and may even enhance their welfare. The study supports the implementation of structured visitor programs for public education and funding, without compromising animal well-being. This contrasts with some previous research in zoo settings, suggesting that controlled visits can be beneficial in primate sanctuaries.

Anthropogenic activities shape animals time allocation and risk perception, yet its immediate behavioural impacts on primate species remain poorly quantified. In the present study, variation in activity budgets and vigilance were analysed in three Cape chacma baboon (Papio ursinus ursinus) troops inhabiting contrasting anthropogenic environments in South Africas Garden Route: Madiba (in a peri-urban campus), North (in an intermediate area), and Outeniqua (in a more rural area). From March to June 2024, a total 84 h of observations were recorded yielding 343 scan samples, and modelled behaviour as a function of troop and environmental covariates (weather, habitat openness, car and human presence). Feeding dominated overall time allocation (35.4%), with no whole-budget differences among troops, but behaviour-specific contrasts emerged. Outeniqua troop inhabiting the more rural area relied significantly less on human-derived foods than Madiba and showed less running than both Madiba and North. In addition, level-3 vigilance (active/intense scanning) was higher in the troops frequenting more anthropogenic environments (Madiba, North) than in Outeniqua, suggesting that vigilance is a particularly sensitive response to human exposure. Finally, habitat openness was negatively associated with affiliative interactions, and car presence was negatively associated with resting. These results provide partial support for hypothesised disturbance effects, with shifts in behavioural sub-categories without overall budget change, clarifying how anthropogenic disturbance can restructure primate time allocation and risk perception. Such immediate behavioural responses should offer actionable insight for evidence-based conservation and human-baboon conflict mitigation.

The hypothesis that dangerous snakes served as evolutionary selective pressures on traits characterizing the Order Primates (Snake Detection Hypothesis, SDH), specifically vision and aspects of the brain, has received recent attention. We provide data on 52 encounters between chimpanzees (Pan troglodytes verus) in a savanna landscape and snakes and other large reptiles at the Fongoli site in Senegal, over the course of eight years. These encounters yielded data on 178 interactions between identified individual chimpanzees and reptiles. The majority of encounters with identified reptiles (62%) involved potentially deadly snakes. Constrictors of the family Pythonidae were encountered more frequently than any other reptile. Chimpanzees exhibited a variety of reactions to reptiles, ranging from attacking with objects to ignoring them. Even reptiles other than snakes were met with some degree of alarm when they were in water or moving quickly. We assessed variables that may affect apes reactions, as well as the age-sex class of chimpanzees. As a test of Isbells snake detection hypothesis, we examined chimpanzees reaction intensity to venomous versus constricting snakes but found no difference. We did find significant age-sex differences in chimpanzees reactions to snakes, with adolescent males exhibiting higher-intensity reactions than adult males and females and adolescent female chimpanzees. Chimpanzees reacted at significantly higher intensities when snakes were arboreal in location, but reptile species, size, and activity did not significantly influence individuals reactions to snakes. We also report one inferred encounter between an adult female chimpanzee and a venomous snake, which led to her death. Our data suggest that snakes are significant threats to chimpanzees in savanna environments and support the hypothesis that danger from snakes could have exerted significant evolutionary pressure on the Order Primates.

The lion-tailed macaque is a gregarious, rainforest-adapted species, that has, in certain locations across its natural distribution, recently begun to explore and utilise surrounding human-dominated habitats. In many primate species, exposure to novel human-use food resources and potential provisioning has previously been associated with changes in intra-group social structure, often categorised by increased aggression and, more importantly, increased affiliation, possibly as a means of reconciliation. Here we quantify the changing affiliative relationships among the female members of two groups with varying degrees of habituation, using social network analysis. We examine frequencies of pair-wise affiliation between the female members of each group, ranked within the prevailing linear hierarchy, to measure individual attributes or the local importance of individuals in a network, and group attributes or the global role of all individuals in the whole network. We found that the subordinate individuals in the less habituated group maintained a higher number of connections with group members, an expected outcome, as key affiliative behaviours such as grooming are known to be directed upwards in the hierarchy. This pattern was observed to be inverse in the highly habituated group, with dominant individuals maintaining more connections, suggesting that under the conditions of increased competition for the novel food resource, dominance rank was highly contested. In support of this theory, we also found multiple fluctuations in dominance rank over time for this highly habituated group, with nearly no fluctuations in the less habituated group. This study demonstrates that varied intensities of human presence and dependence on human-use foods have differential effects on the intra-group sociality of lion-tailed macaques.

Gibbons are known as one of the most vocal non-human primates. They vocally advertise and reinforce their pair-bonds by singing complex duets, in which both the male and female perform a predetermined sex-specific set of song phrases, including the loud and elongated great-calls. Only females and sub-adult male gibbons have been previously observed performing great-calls. Once a male gibbon matures, he normally stops great-call production completely but continues singing other and less high-pitched song phrases. This case study describes a fully adult, castrated male lar gibbon (Hylobates lar, 32 years old, zoo-housed) who performs both male phrases of the duet, including the female great-call. The male regularly produced great-calls despite being in a, relatively weak, pair bond with a female conspecific. His great-calls adhered to the general structure of typical female great-calls but were shorter and had a lower maximum frequency. Notably, he produced these great-calls predominantly when the female was absent, especially when she was in their inside enclosure whilst he was outside. Behavioural observations indicate that the occurrence of great-calls by the male cannot be predicted based on pre-song behaviour or his interaction with the female. The recurrence of sub-adult singing behaviour in a fully grown adult is most likely due to his reduced testosterone levels. This study sheds light on the intricate dynamics of duetting and the unique occurrence of cross-sex song production in gibbons, emphasizing the complexity of pair-bond communication in this species.

Primate evolution has been dominated above all by increases in brain size over time. Here I show that two separate pressures have been responsible for substantial changes in the major structural features of the primate brain. Lineages that have adopted pairliving are associated with a differential increase in the volume of the subcortical brain. This mainly reflects an increase in body size and a consequent need to invest in cerebellum size in order to manage large body masses in three-dimensional arboreal environments, a trend that continues through the great apes. The second trajectory is associated with a switch to group-living, and is associated with a progressive increase in neocortex volume. This seems to have occurred in three distinct waves corresponding to stepwise increases in social group size. These trends are not associated with phylogeny, but represent taxonomically mosaic evolution driven by individual species exposure to new kinds of habitats.

The critically endangered white-thighed colobus, Colobus vellerosus, is on the brink of extinction, necessitating the implementation of effective conservation management strategies. The population in Kikele village serves as the primary remaining stronghold for this species in Benin, comprising around twenty-eight individuals in the small Kikele Sacred Forest and an additional eight individuals in the community-managed Okuta Kobunan Forest. These two populations are believed to have descended from a single founding pair introduced to the Kikele region circa 1800. Given the small population size and the possible severe genetic bottleneck at its foundation, the genetic diversity might be extremely low. In our study, we conducted a first analysis of the genetic diversity of the two populations using mitochondrial markers, the complete cytochrome b (cytb) and a segment of the hypervariable control region (D-loop, 750 bp). Our findings revealed only one cytb haplotype, along with two haplotypes that differ by just one site in the D-loop. We recommend a range-wide population genetic assessment of the species to explore the possibility of translocations as a potential genetic rescue strategy.

In the process of vocal learning, animals give immature vocalization, such as babbling and subsong. Here I report a characteristic vocalization given by a subspecies of large-billed crow, Corvus macrorhynchos osai, that live in Kuroshima Island, Okinawa, Japan. This vocalization (type-K) is characterized by very rapid bill movements (ca. 13 times/sec). The type-K was heard throughout the island, indicating that the population of the Kuroshima Island share this call type. In addition, a juvenile crow was observed giving immature type-K repeatedly. This observation suggests that this call type is not innate but acquired through vocal learning.

Many primates exhibit female philopatry and live in stable, female-bonded social groups. Permanent group fusions are rarely documented in these populations. We present a case study on a fusion of two social groups from a hybrid population of baboons (Papio cynocephalus x P. anubis) living in the Amboseli basin of Kenya. The fusion occurred following a period of increased human-induced mortality in one of the two social groups. After the fusion, females from the smaller group became the lowest ranking. We compared female behavior in the months following the fusion to the behavior of females in groups that had not fused and also compared pre- and post-fusion fitness outcomes. Following the fusion, the groups activity budget and patterns of agonistic interactions were typical for the study population. Females preferred familiar grooming partners for a short period following the fusion; however, after three months, patterns in female grooming were comparable to other groups, indicating rapid social integration. With the caveat that our sample size was limited, we observed no detectable fitness-related costs of group fusion in terms of birth rates or offspring survival, and adult female mortality was low following the fusion. These results demonstrate the flexibility of female baboons in navigating exposure to novel same-sex conspecifics despite a species-typic pattern of female philopatry. Based on this and previous examples of group fusions, we propose that group fusions may be most likely to occur when groups are too small to retain adult males, defend against predators, or compete with other groups.

Lethal gang attacks, in which multiple aggressors attack a single victim, are among the most widespread forms of violence between human groups. Chimpanzees (Pan troglodytes), as well as wolves (Canis lupus), spotted hyaenas (Crocuta crocuta), and lions (Panthera leo), perform gang attacks during raids. In raids, a few individuals of a group enter another groups territory and attack its members if found in numerical disadvantage. Current theory predicts that raids and gang attacks are linked to fission-fusion dynamics, i.e., the capacity of a group to split into smaller subgroups of variable size and composition. However, over the last decade, research on social mammals without fission-fusion societies nor raiding have shown that they may also be involved in intergroup lethal gang attacks. Thus, neither fission-fusion dynamics nor raiding are required for gang attacks to evolve. Based on our first-ever reports of intergroup gang attacks in the crested macaque (Macaca nigra), combined with the synthesis of earlier observations of such attacks in several species living in stable groups, we develop a new hypothesis about the proximate causes leading to lethal intergroup aggression. We propose that the ability to estimate numerical odds, form coalitionary bonds, and show hostility towards outgroup individuals may suffice to trigger intergroup gang attacks when the conditions favour an imbalance of power between victims and attackers.

Contrary to previous beliefs, intentional gestural communication (IGC) is not exclusive to the hominoid lineage but is also present in other non-human primates. Here, we report the presence of IGC among free-ranging Hanuman langur troop in Dakshineswar, West Bengal, India. These langurs exhibit a food-requesting behaviour wherein they use several gestures to communicate with the humans nearby. Moreover, they can also assess the recipients mental state and persistently check if the signal (food request) has been received, waiting until they receive the desired food item. We have identified eight begging gestures used by langurs of all ages, except infants. The most common gesture is by holding cloth (BGc), but provocation-initiated begging (BGpi) and begging by embracing legs (BGe) efficiently direct these events to its success. The frequency of successful begging events is higher in the evening due to increased human interactions. Our findings suggest that ontogenetic ritualization might be at play here among these troop members as this gestural communication has been learned through imitation and reinforced by the reward of receiving food. Moreover, these successful begging events serve as an effective foraging strategy for urban-adapted langurs, allowing them to acquire high-calorie processed food items within a human-modified urban ecosystem.