Chimpanzees routinely fish for algae with tools during the dry season in Bakoun, Guinea

Chimpanzees employ context-specific behavioral strategies within fission-fusion societies

Fission-fusion social systems allow individuals to make flexible choices about where, with whom, and in what contexts to spend their time in response to competing social and ecological pressures. The ability for fission-fusion societies to support individual behavioral strategies that vary across contexts has been suggested, but the potential function of such context-specific social choices remains largely understudied. We adopted the concept of social niche construction to explore possible differences in social complexity at the individual and group level across feeding contexts. Specifically, we examined patterns of co-attendance across two common ecological contexts in wild Central African chimpanzees (Pan troglodytes troglodytes) in the Goualougo Triangle, Republic of Congo. From data compiled over 6 years, we used multidimensional social network analysis to study the patterns of co-attendance generated from 436 group scans at Ficus and 4527 visits to termite mounds. These two contexts were chosen, because they are both fixed spatial features across the landscape that serve as well-defined points to compare association patterns. We identified context-specific social niche construction in a fission-fusion chimpanzee society that produce different patterns of relationships and social complexity that are consistent in their expression over many years, and offer functional benefits. While enhancing our understanding of chimpanzee behavioral strategies, culture, and conservation, our investigation also indicates that the social niche construction framework aids in elucidating the evolutionary advantages of fission-fusion sociality by accounting for intra- and interindividual variability, cognition, and choice in newfound ways.

Flexible grouping patterns in a western and eastern chimpanzee community

Primate social organizations, or grouping patterns, vary significantly across species. Behavioral strategies that allow for flexibility in grouping patterns offer a means to reduce the costs of group living. Chimpanzees (Pan troglodytes) have a fission-fusion social system in which temporary subgroups ("parties") change in composition because of local socio-ecological conditions. Notably, western chimpanzees (P. t. verus) are described as showing a higher degree of bisexual bonding and association than eastern chimpanzees, and eastern female chimpanzees (P. t. schweinfurthii) are thought to be more solitary than western female chimpanzees. However, reported comparisons in sociality currently depend on a small number of study groups, particularly in western chimpanzees, and variation in methods. The inclusion of additional communities and direct comparison using the same methods are essential to assess whether reported subspecies differences in sociality hold in this behaviorally heterogeneous species. We explored whether sociality differs between two communities of chimpanzees using the same motion-triggered camera technology and definitions of social measures. We compare party size and composition (party type, sex ratio) between the western Gahtoy community in the Nimba Mountains (Guinea) and the eastern Waibira community in the Budongo Forest (Uganda). Once potential competition for resources such as food and mating opportunities were controlled for, subspecies did not substantially influence the number of individuals in a party. We found a higher sex-ratio, indicating more males in a party, in Waibira; this pattern was driven by a greater likelihood in Gahtoy to be in all-female parties. This finding is the opposite of what was expected for eastern chimpanzees, where female-only parties are predicted to be more common. Our results highlight the flexibility in chimpanzee sociality, and caution against subspecies level generalizations.

Primate archaeology 3.0

The new field of primate archaeology investigates the technological behavior and material record of nonhuman primates, providing valuable comparative data on our understanding of human technological evolution. Yet, paralleling hominin archaeology, the field is largely biased toward the analysis of lithic artifacts. While valuable comparative data have been gained through an examination of extant nonhuman primate tool use and its archaeological record, focusing on this one single aspect provides limited insights. It is therefore necessary to explore to what extent other non-technological activities, such as non-tool aided feeding, traveling, social behaviors or ritual displays, leave traces that could be detected in the archaeological record. Here we propose four new areas of investigation which we believe have been largely overlooked by primate archaeology and that are crucial to uncovering the full archaeological potential of the primate behavioral repertoire, including that of our own: (1) Plant technology; (2) Archaeology beyond technology; (3) Landscape archaeology; and (4) Primate cultural heritage. We discuss each theme in the context of the latest developments and challenges, as well as propose future directions. Developing a more "inclusive" primate archaeology will not only benefit the study of primate evolution in its own right but will aid conservation efforts by increasing our understanding of changes in primate-environment interactions over time.

Camera traps unveil demography, social structure, and home range of six unhabituated Western chimpanzee groups in the Moyen Bafing National Park, Guinea

Precise estimates of population dynamics and social grouping patterns are required for effective conservation of wild animal populations. It is difficult to obtain such information on non-human great apes as they have slow reproductive rates. To gain a better understanding of demography in these populations, previous research has typically involved habituation\, a process that requires years. Here, we collected data continuously over year-long periods to monitor an unhabituated population of critically endangered Western chimpanzees (Pan troglodytes verus) in the Moyen Bafing National Park, Guinea. We used two arrays of 100 camera traps that were placed opportunistically in two distinct 100 km2 sites, named Bakoun and Koukoutamba. We identified 227 individuals in Bakoun and 207 in Koukoutamba through their unique facial features. Our camera trap data make clear that these individuals belong to six and seven closed groups, respectively. Six of those groups were near-completely sampled with an average minimum size of 46.8 individuals (range: 37-58), and a mean adult sex ratio of 1.32 (range: 0.93-2.10). We described the demographic composition of these groups and use Bayesian social network analysis to understand population structure. The network analyses suggested that the social bonds within the two populations were structured by sex homophily, with male chimpanzees being more or equally likely to be observed together than other adult associations. Through estimation of minimum convex polygons, we described the minimum home range for those groups. Compared to other chimpanzee groups living in a similar environment (mosaic savanna-forest), the Moyen Bafing region seems to host a high-density of chimpanzees with small home ranges for their group size. Our research highlights the potential of camera traps for studying the demographic composition of chimpanzee populations with high resolution and obtaining crucial information on several groups in a time-efficient and cost-effective way.

Landscaping the Behavioural Ecology of Primate Stone Tool Use

Ecology is fundamental in the development, transmission, and perpetuity of primate technology. Previous studies on tool site selection have addressed the relevance of targeted resources and raw materials for tools, but few have considered the broader foraging landscape. In this landscape-scale study of the ecological contexts of wild chimpanzee (Pan troglodytes verus) tool use, we investigated the conditions required for nut-cracking to occur and persist in discrete locations at the long-term field site of Bossou, Guinea. We examined this at three levels: selection, frequency of use, and inactivity. We collected data on plant foods, nut trees, and raw materials using transect and quadrat methods, and conducted forest-wide surveys to map the location of nests and watercourses. We analysed data at the quadrat level (n = 82) using generalised linear models and descriptive statistics. We found that, further to the presence of a nut tree and availability of raw materials, abundance of food-providing trees as well as proximity to nest sites were significant predictors of nut-cracking occurrence. This suggests that the spatial distribution of nut-cracking sites is mediated by the broader behavioural landscape and is influenced by non-extractive foraging of perennial resources and non-foraging activities. Additionally, the number of functional tools was greater at sites with higher nut-cracking frequency, and was negatively correlated with site inactivity. Our research indicates that the technological landscape of Bossou chimpanzees shares affinities with the ‘favoured places’ model of hominin site formation, providing a comparative framework for reconstructing landscape-scale patterns of ancient human behaviour. A French translation of this abstract is provided in theelectronic supplementary information: EMS 2.

Phenotypic and genetic associations between gray matter covariation and tool use skill in chimpanzees (Pan troglodytes): Repeatability in two genetically isolated populations

Humans and chimpanzees both exhibit a diverse set of tool use skills which suggests selection for tool manufacture and use occurred in the common ancestors of the two species. Our group has previously reported phenotypic and genetic associations between tool use skill and gray matter covariation, as quantified by source-based morphometry (SBM), in chimpanzees. As a follow up study, here we evaluated repeatability in heritability in SBM components and their phenotypic association with tool use skill in two genetically independent chimpanzee cohorts. Within the two independent cohorts of chimpanzees, we identified 8 and 16 SBM components, respectively. Significant heritability was evident for multiple SBM components within both cohorts. Further, phenotypic associations between tool use performance and the SBM components were largely consistent between the two cohorts; the most consistent finding being an association between tool use performance and an SBM component including the posterior superior temporal sulcus (STS) and superior temporal gyrus (STG), and the interior and superior parietal regions (p< 0.05). These findings indicate that the STS, STG, and parietal cortices are phenotypically and genetically implicated in chimpanzee tool use abilities.

Cost-Benefit Trade-Offs of Aquatic Resource Exploitation in the Context of Hominin Evolution

While the exploitation of aquatic fauna and flora has been documented in several primate species to date, the evolutionary contexts and mechanisms behind the emergence of this behavior in both human and non-human primates remain largely overlooked. Yet, this issue is particularly important for our understanding of human evolution, as hominins represent not only the primate group with the highest degree of adaptedness to aquatic environments, but also the only group in which true coastal and maritime adaptations have evolved. As such, in the present study we review the available literature on primate foraging strategies related to the exploitation of aquatic resources and their putative associated cognitive operations. We propose that aquatic resource consumption in extant primates can be interpreted as a highly site-specific behavioral expression of a generic adaptive foraging decision-making process, emerging in sites at which the local cost-benefit trade-offs contextually favor aquatic over terrestrial foods. Within this framework, we discuss the potential impacts that the unique intensification of this behavior in hominins may have had on the evolution of the human brain and spatial ecology.

Quantitative estimates of glacial refugia for chimpanzees (Pan troglodytes) since the Last Interglacial (120,000 BP)

Paleoclimate reconstructions have enhanced our understanding of how past climates have shaped present-day biodiversity. We hypothesize that the geographic extent of Pleistocene forest refugia and suitable habitat fluctuated significantly in time during the late Quaternary for chimpanzees (Pan troglodytes). Using bioclimatic variables representing monthly temperature and precipitation estimates, past human population density data, and an extensive database of georeferenced presence points, we built a model of changing habitat suitability for chimpanzees at fine spatio-temporal scales dating back to the Last Interglacial (120,000 BP). Our models cover a spatial resolution of 0.0467° (approximately 5.19 km² grid cells) and a temporal resolution of between 1000 and 4000 years. Using our model, we mapped habitat stability over time using three approaches, comparing our modeled stability estimates to existing knowledge of Afrotropical refugia, as well as contemporary patterns of major keystone tropical food resources used by chimpanzees, figs (Moraceae), and palms (Arecacae). Results show habitat stability congruent with known glacial refugia across Africa, suggesting their extents may have been underestimated for chimpanzees, with potentially up to approximately 60,000 km² of previously unrecognized glacial refugia. The refugia we highlight coincide with higher species richness for figs and palms. Our results provide spatio-temporally explicit insights into the role of refugia across the chimpanzee range, forming the empirical foundation for developing and testing hypotheses about behavioral, ecological, and genetic diversity with additional data. This methodology can be applied to other species and geographic areas when sufficient data are available.

Captive great apes tend to innovate simple tool behaviors quickly

Recent studies have highlighted the important role that individual learning mechanisms and different forms of enhancenment play in the acquisition of novel behaviors by naïve individuals. A considerable subset of these studies has focused on tool innovation by our closest living relatives, the great apes, to better undestand the evolution of technology in our own lineage. To be able to isolate the role that individual learning plays in great ape tool innovation, researchers usually employ what are known as baseline tests. Although these baselines are commonly used in behavioral studies in captivity, the length of these tests in terms of number of trials and duration remains unstandarized across studies. To address this methodological issue, we conducted a literature review of great ape tool innovation studies conducted in zoological institutions and compiled various methodological data including the timing of innovation. Our literature review revealed an early innovation tendency in great apes, which was particularly pronounced when simple forms of tool use were investigated. In the majority of experiments where tool innovation took place, this occurred within the first trial and/or the first hour of testing. We discuss different possible sources of variation in the latency to innovate such as testing setup, species and task. We hope that our literature review helps researchers design more data-informed, resource-efficient experiments on tool innovation in our closest living relatives.

Western chimpanzees (Pan troglodytes verus) access a nutritionally balanced, high energy, and abundant food, baobab (Adansonia digitata) fruit, with extractive foraging and reingestion

Intrinsic to several hypotheses explaining the evolution of foraging behavior complexity, such as proto-tool use, is the assumption that more complex ingestive behaviors are adaptations allowing individuals to access difficult to procure but nutritionally or energetically rewarding foods. However, nutritional approaches to understanding this complexity have been underutilized. The goal of this study was to evaluate potential nutritional determinants of two unusual foraging behaviors, fruit cracking with anvils and seed reingestion, by adult male western chimpanzees (Pan troglodytes verus) at Fongoli, Senegal during the baobab (Adansonia digitata) fruit season. We examined these behaviors in relation to nutrient and energy intake, and compared macronutrient and energy concentrations found in baobab fruits to other plant foods. Adult males ingested at least 31 distinct foods from 23 plant species. Baobab fruit comprised the majority of daily energy intake (68 ± 34%, range: 0%-98%). The energetic concentration of baobab fruit varied by phenophase and part ingested, with ripe and semi-ripe fruit ranking high in energy return rate. Males preferred ripe and semi-ripe baobab fruit but unripe fruit intake was higher overall. The seed kernels were high in protein and fat relative to fruit pulp, and these kernels were easier to access during the unripe stage. During the ripe stage, seed kernels were accessible by reingestion, after the seed coat was softened during gut passage. In addition to providing macronutrients and energy, baobab fruit was a relatively abundant food source. We conclude that baobab pulp and seed are high quality foods at Fongoli during the baobab season because they are nutritionally balanced, high in energy, and relatively abundant in the environment. These nutritional and abundance characteristics may explain, in part, why these chimpanzees use anvils and reingestion to access a mechanically challenging food.

Structure of Chimpanzee Gut Microbiomes across Tropical Africa

Understanding variation in host-associated microbial communities is important given the relevance of microbiomes to host physiology and health. Using 560 fecal samples collected from wild chimpanzees (Pan troglodytes) across their range, we assessed how geography, genetics, climate, vegetation, and diet relate to gut microbial community structure (prokaryotes, eukaryotic parasites) at multiple spatial scales. We observed a high degree of regional specificity in the microbiome composition, which was associated with host genetics, available plant foods, and potentially with cultural differences in tool use, which affect diet. Genetic differences drove community composition at large scales, while vegetation and potentially tool use drove within-region differences, likely due to their influence on diet. Unlike industrialized human populations in the United States, where regional differences in the gut microbiome are undetectable, chimpanzee gut microbiomes are far more variable across space, suggesting that technological developments have decoupled humans from their local environments, obscuring regional differences that could have been important during human evolution.

IMPORTANCE Gut microbial communities are drivers of primate physiology and health, but the factors that influence the gut microbiome in wild primate populations remain largely undetermined. We report data from a continent-wide survey of wild chimpanzee gut microbiota and highlight the effects of genetics, vegetation, and potentially even tool use at different spatial scales on the chimpanzee gut microbiome, including bacteria, archaea, and eukaryotic parasites. Microbial community dissimilarity was strongly correlated with chimpanzee population genetic dissimilarity, and vegetation composition and consumption of algae, honey, nuts, and termites were potentially associated with additional divergence in microbial communities between sampling sites. Our results suggest that host genetics, geography, and climate play a far stronger role in structuring the gut microbiome in chimpanzees than in humans.

Ontogeny and sex differences in object manipulation and probe tool use by wild tufted capuchin monkeys (Sapajus libidinosus)

Tufted capuchin monkeys (Sapajus spp.) are the only Neotropical Primates that regularly use tools in the wild, but only one population of bearded capuchin monkeys (Sapajus libidinosus) is known to habitually use sticks as probes. In this population, males are typically the only sex to use stick tools, something unexpected, since there are no obvious physical constraints, and females do use stone tools in the wild and sticks in experimental conditions. We investigated the development of probe tool use in eight infants to clarify whether social influences on learning varied between the sexes, as tool use learning by capuchin monkeys is a socially biased process. We found that in the first 10 months of age, females manipulate sticks as much as males, but after 10-12 months of age, males begin to manipulate them at higher frequencies. We examined if social connections-as opportunities for social learning-could explain this difference and verified that, on close distance social networks, infant males and females have similar connections with older males. However, males observe probe tool use events more often than females when close to such events. The higher frequency of manipulation of sticks, as well as the higher rates of probe tool use observation, appear to be the key to understand why only males are probe tool users in this population. Since there are only male potential models of probe use, a sex motivational bias could explain the sex difference in observation; a bias in observation could explain the differences in manipulation-and manipulation rates would certainly influence the chances of individual, trial-and-error learning (a case of "local/stimulus enhancement").

Limited evidence of C4 plant consumption in mound building Macrotermes termites from savanna woodland chimpanzee sites

Stable isotope analysis is an increasingly used molecular tool to reconstruct the diet and ecology of elusive primates such as unhabituated chimpanzees. The consumption of C4 plant feeding termites by chimpanzees may partly explain the relatively high carbon isotope values reported for some chimpanzee communities. However, the modest availability of termite isotope data as well as the diversity and cryptic ecology of termites potentially consumed by chimpanzees obscures our ability to assess the plausibility of these termites as a C4 resource. Here we report the carbon and nitrogen isotope values from 79 Macrotermes termite samples from six savanna woodland chimpanzee research sites across equatorial Africa. Using mixing models, we estimated the proportion of Macrotermes C4 plant consumption across savanna woodland sites. Additionally, we tested for isotopic differences between termite colonies in different vegetation types and between the social castes within the same colony in a subset of 47 samples from 12 mounds. We found that Macrotermes carbon isotope values were indistinguishable from those of C3 plants. Only 5 to 15% of Macrotermes diets were comprised of C4 plants across sites, suggesting that they cannot be considered a C4 food resource substantially influencing the isotope signatures of consumers. In the Macrotermes subsample, vegetation type and caste were significantly correlated with termite carbon values, but not with nitrogen isotope values. Large Macrotermes soldiers, preferentially consumed by chimpanzees, had comparably low carbon isotope values relative to other termite castes. We conclude that Macrotermes consumption is unlikely to result in high carbon isotope values in either extant chimpanzees or fossil hominins.

Chimpanzee identification and social network construction through an online citizen science platform

Citizen science has grown rapidly in popularity in recent years due to its potential to educate and engage the public while providing a means to address a myriad of scientific questions. However, the rise in popularity of citizen science has also been accompanied by concerns about the quality of data emerging from citizen science research projects. We assessed data quality in the online citizen scientist platform Chimp&See, which hosts camera trap videos of chimpanzees (Pan troglodytes) and other species across Equatorial Africa. In particular, we compared detection and identification of individual chimpanzees by citizen scientists with that of experts with years of experience studying those chimpanzees. We found that citizen scientists typically detected the same number of individual chimpanzees as experts, but assigned far fewer identifications (IDs) to those individuals. Those IDs assigned, however, were nearly always in agreement with the IDs provided by experts. We applied the data sets of citizen scientists and experts by constructing social networks from each. We found that both social networks were relatively robust and shared a similar structure, as well as having positively correlated individual network positions. Our findings demonstrate that, although citizen scientists produced a smaller data set based on fewer confirmed IDs, the data strongly reflect expert classifications and can be used for meaningful assessments of group structure and dynamics. This approach expands opportunities for social research and conservation monitoring in great apes and many other individually identifiable species.

Environmental variability supports chimpanzee behavioural diversity

Large brains and behavioural innovation are positively correlated, species-specific traits, associated with the behavioural flexibility animals need for adapting to seasonal and unpredictable habitats. Similar ecological challenges would have been important drivers throughout human evolution. However, studies examining the influence of environmental variability on within-species behavioural diversity are lacking despite the critical assumption that population diversification precedes genetic divergence and speciation. Here, using a dataset of 144 wild chimpanzee (Pan troglodytes) communities, we show that chimpanzees exhibit greater behavioural diversity in environments with more variability — in both recent and historical timescales. Notably, distance from Pleistocene forest refugia is associated with the presence of a larger number of behavioural traits, including both tool and non-tool use behaviours. Since more than half of the behaviours investigated are also likely to be cultural, we suggest that environmental variability was a critical evolutionary force promoting the behavioural, as well as cultural diversification of great apes.

Environmental variability is one potential driver of behavioural and cultural diversity in humans and other animals. Here, the authors show that chimpanzee behavioural diversity is higher in habitats that are more seasonal and historically unstable, and in savannah woodland relative to forested sites.

Chimpanzee ethnography reveals unexpected cultural diversity

Human ethnographic knowledge covers hundreds of societies, whereas chimpanzee ethnography encompasses at most 15 communities. Using termite fishing as a window into the richness of chimpanzee cultural diversity, we address a potential sampling bias with 39 additional communities across Africa. Previously, termite fishing was known from eight locations with two distinguishable techniques observed in only two communities. Here, we add nine termite-fishing communities not studied before, revealing 38 different technical elements, as well as community-specific combinations of three to seven elements. Thirty of those were not ecologically constrained, permitting the investigation of chimpanzee termite-fishing culture. The number and combination of elements shared among individuals were more similar within communities than between them, thus supporting community-majority conformity via social imitation. The variation in community-specific combinations of elements parallels cultural diversity in human greeting norms or chopstick etiquette. We suggest that termite fishing in wild chimpanzees shows some elements of cumulative cultural diversity.

How to measure chimpanzee party size? A methodological comparison

Chimpanzees (Pan troglodytes) live in fission-fusion societies where community members form temporary parties that frequently change in size and composition. Chimpanzee party size and composition have been widely studied to identify proximate causes of grouping patterns, and party size estimates are used to assess population sizes and densities. Numerous socio-ecological factors influence chimpanzee party size, but findings differ across studies. Various methods to measure party size exist, including direct observations, motion-triggered camera (MTC) observations, and nest counts. However, comparative analyses of these methods are lacking. Here, we assess relative differences in four commonly used party size methods and we examine socio-ecological factors influencing party size of unhabituated chimpanzees (P. t. verus) at Seringbara, Nimba, Guinea. We also assess which method(s) best reflect the influence of socio-ecological factors on party size. Using data collected over 69 months, we show that night nest counts resulted in relatively larger party size estimates than the other methods, and day nest counts resulted in relatively smaller party size estimates. Direct and MTC observations did not differ in relative estimates of party size and composition. Both fruit abundance and presence of estrous females positively influenced party size, but this effect was only evident when measuring party size with MTCs. Methods thus differ in relative party size estimates and their ability to assess the impact of socio-ecological factors. We conclude that MTC observations best represent party size and the effect of socio-ecological factors at Nimba. MTCs show promising potential for studying grouping patterns in unhabituated chimpanzees.

Further evidence of a left hemisphere specialization and genetic basis for tool use skill in chimpanzees (Pan troglodytes): Reproducibility in two genetically isolated populations of apes

It has been hypothesized that the evolution of tool use may have served as a preadaptation for the emergence of left hemispheric specialization in motor skill in humans. Here, we tested for intermanual differences in performance on a tool use task in a sample of 206 captive chimpanzees in relation to their sex, age, and hand preference. In addition, we examined heritability in tool use skill for the entire sample, as well as within 2 genetically isolated populations of captive chimpanzees. This was done to determine the degree of reproducibility in heritability on motor performance. The results revealed a significant effect of hand preference on intermanual differences in performance. Right-handed chimpanzees performed the task more quickly with their right compared with left hand. In contrast, no significant intermanual differences in performance were found in left- and ambiguous-handed apes. Tool use performance was found to be significantly heritable for overall performance, as well as separately for the left and right hands. Further, significant heritability in tool use performance was found in both populations of apes, suggesting these results were reproducible. The results are discussed in the context of evolutionary theories of handedness and hemispheric specialization and the genetic mechanisms that underlie their expression in primates, including humans. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Novelty Response of Wild African Apes to Camera Traps

Temperament and personality research in humans and nonhuman animals measures behavioral variation in individual, population, or species-specific traits with implications for survival and fitness, such as social status, foraging, and mating success [1-5]. Curiosity and risk-taking tendencies have been studied extensively across taxa by measuring boldness and exploration responses to experimental novelty exposure [3, 4, 6-15]. Here, we conduct a natural field experiment using wildlife monitoring technology to test variation in the reaction of wild great apes (43 groups of naive chimpanzees, bonobos, and western gorillas across 14 field sites in Africa) to a novel object, the camera trap. Bonobo and gorilla groups demonstrated a stronger looking impulse toward the camera trap device compared to chimpanzees, suggesting higher visual attention and curiosity. Bonobos were also more likely to show alarm and other fearful behaviors, although such neophobic (and conversely, neophilic) responses were generally rare. Among all three species, individuals looked at cameras longer when they were young, were associating with fewer individuals, and did not live near a long-term research site. Overall, these findings partially validate results from great ape novelty paradigms in captivity [7, 8]. We further suggest that species-typical leadership styles [16] and social and environmental effects, including familiarity with humans, best explain novelty responses of wild great apes. In sum, this study illustrates the feasibility of large-scale field experiments and the importance of both intrinsic and extrinsic factors in shaping animal curiosity. VIDEO ABSTRACT.

Human impact erodes chimpanzee behavioral diversity

Chimpanzees possess a large number of behavioral and cultural traits among nonhuman species. The "disturbance hypothesis" predicts that human impact depletes resources and disrupts social learning processes necessary for behavioral and cultural transmission. We used a dataset of 144 chimpanzee communities, with information on 31 behaviors, to show that chimpanzees inhabiting areas with high human impact have a mean probability of occurrence reduced by 88%, across all behaviors, compared to low-impact areas. This behavioral diversity loss was evident irrespective of the grouping or categorization of behaviors. Therefore, human impact may not only be associated with the loss of populations and genetic diversity, but also affects how animals behave. Our results support the view that "culturally significant units" should be integrated into wildlife conservation.

Nocturnal activity in wild chimpanzees (Pan troglodytes): Evidence for flexible sleeping patterns and insights into human evolution

OBJECTIVES

We investigated occurrences and patterns of terrestrial nocturnal activity in wild chimpanzees (Pan troglodytes) and modelled the influence of various ecological predictors on nocturnal activity.

METHODS

Data were extracted from terrestrial camera-trap footage and ecological surveys from 22 chimpanzee study sites participating in the Pan African Programme: The Cultured Chimpanzee. We described videos demonstrating nocturnal activity, and we tested the effects of the percentage of forest, abundance of predators (lions, leopards and hyenas), abundance of large mammals (buffalos and elephants), average daily temperature, rainfall, human activity, and percent illumination on the probability of nocturnal activity.

RESULTS

We found terrestrial nocturnal activity to occur at 18 of the 22 study sites, at an overall average proportion of 1.80% of total chimpanzee activity, and to occur during all hours of the night, but more frequently during twilight hours. We found a higher probability of nocturnal activity with lower levels of human activity, higher average daily temperature, and at sites with a larger percentage of forest. We found no effect of the abundance of predators and large mammals, rainfall, or moon illumination.

DISCUSSION

Chimpanzee terrestrial nocturnal activity appears widespread yet infrequent, which suggests a consolidated sleeping pattern. Nocturnal activity may be driven by the stress of high daily temperatures and may be enabled at low levels of human activity. Human activity may exert a relatively greater influence on chimpanzee nocturnal behavior than predator presence. We suggest that chimpanzee nocturnal activity is flexible, enabling them to respond to changing environmental factors.

Non-invasive genetic censusing and monitoring of primate populations

Knowing the density or abundance of primate populations is essential for their conservation management and contextualizing socio-demographic and behavioral observations. When direct counts of animals are not possible, genetic analysis of non-invasive samples collected from wildlife populations allows estimates of population size with higher accuracy and precision than is possible using indirect signs. Furthermore, in contrast to traditional indirect survey methods, prolonged or periodic genetic sampling across months or years enables inference of group membership, movement, dynamics, and some kin relationships. Data may also be used to estimate sex ratios, sex differences in dispersal distances, and detect gene flow among locations. Recent advances in capture-recapture models have further improved the precision of population estimates derived from non-invasive samples. Simulations using these methods have shown that the confidence interval of point estimates includes the true population size when assumptions of the models are met, and therefore this range of population size minima and maxima should be emphasized in population monitoring studies. Innovations such as the use of sniffer dogs or anti-poaching patrols for sample collection are important to ensure adequate sampling, and the expected development of efficient and cost-effective genotyping by sequencing methods for DNAs derived from non-invasive samples will automate and speed analyses.

DNA recovery from wild chimpanzee tools

Most of our knowledge of wild chimpanzee behaviour stems from fewer than 10 long-term field sites. This bias limits studies to a potentially unrepresentative set of communities known to show great behavioural diversity on small geographic scales. Here, we introduce a new genetic approach to bridge the gap between behavioural material evidence in unhabituated chimpanzees and genetic advances in the field of primatology. The use of DNA analyses has revolutionised archaeological and primatological fields, whereby extraction of DNA from non-invasively collected samples allows researchers to reconstruct behaviour without ever directly observing individuals. We used commercially available forensic DNA kits to show that termite-fishing by wild chimpanzees (Pan troglodytes schweinfurthii) leaves behind detectable chimpanzee DNA evidence on tools. We then quantified the recovered DNA, compared the yield to that from faecal samples, and performed an initial assessment of mitochondrial and microsatellite markers to identify individuals. From 49 termite-fishing tools from the Issa Valley research site in western Tanzania, we recovered an average of 52 pg/μl chimpanzee DNA, compared to 376.2 pg/μl in faecal DNA extracts. Mitochondrial DNA haplotypes could be assigned to 41 of 49 tools (84%). Twenty-six tool DNA extracts yielded >25 pg/μl DNA and were selected for microsatellite analyses; genotypes were determined with confidence for 18 tools. These tools were used by a minimum of 11 individuals across the study period and termite mounds. These results demonstrate the utility of bio-molecular techniques and a primate archaeology approach in non-invasive monitoring and behavioural reconstruction of unhabituated primate populations.

Tool Use: Crows Craft the Right Tool for the Job

New research into tool crafting in New Caledonian crows has uncovered factors that influence tool shape and the foraging advantages that these characteristics confer.

Spontaneous reoccurrence of "scooping", a wild tool-use behaviour, in naïve chimpanzees

Modern human technological culture depends on social learning. A widespread assumption for chimpanzee tool-use cultures is that they, too, are dependent on social learning. However, we provide evidence to suggest that individual learning, rather than social learning, is the driver behind determining the form of these behaviours within and across individuals. Low-fidelity social learning instead merely facilitates the reinnovation of these behaviours, and thus helps homogenise the behaviour across chimpanzees, creating the population-wide patterns observed in the wild (what here we call "socially mediated serial reinnovations"). This is the main prediction of the Zone of Latent Solutions (ZLS) hypothesis. This study directly tested the ZLS hypothesis on algae scooping, a wild chimpanzee tool-use behaviour. We provided naïve chimpanzees (n = 14, Mage = 31.33, SD = 10.09) with ecologically relevant materials of the wild behaviour but, crucially, without revealing any information on the behavioural form required to accomplish this task. This study found that naïve chimpanzees expressed the same behavioural form as their wild counterparts, suggesting that, as the ZLS theory predicts, individual learning is the driver behind the frequency of this behavioural form. As more behaviours are being found to be within chimpanzee's ZLS, this hypothesis now provides a parsimonious explanation for chimpanzee tool cultures.