Referential gestures are not ubiquitous in wild chimpanzees : alternative functions for exaggerated loud scratch gestures

Royal Zoological Society of Scotland for providing core funding for Budongo Conservation Field Station. This work was supported by the ERC grant awarded to KS (ERC_CoG 2016_724608).A fundamental aspect of human communication is our ability to refer to external objects and events through both words and gestures (such as pointing), yet the evolutionary origins of such signals remain obscure. Apes, living in their natural environments, rarely or never point, but it has been claimed that male chimpanzees, Pan troglodytes schweinfurthii, from the Ngogo community, Uganda, habitually use exaggerated loud scratches (ELSs) to refer to specific body locations where they wish to be groomed (Pika & Mitani, 2006, Current Biology, 16(6), 191–192). This study suggested continuity between referential abilities in humans and our closest living relatives, making it an important finding to replicate in other populations. Hence here, we compared whether ELSs are used in a referential manner across four wild communities of eastern chimpanzees (Ngogo, Kanyawara, Sonso and Waibira). Our data show that scratchers were significantly more likely to receive grooming in the scratched location at Ngogo compared to the other three sites. At the latter sites this response occurred at low rates and signallers did not seem to pursue this goal. This suggests that ELSs do not function referentially at these sites, and the published findings from Ngogo were not replicated. Further exploration into alternative functions of ELSs in the Kanyawara community revealed that, in this community, this signal functions to initiate grooming bouts and to reengage partners during grooming pauses. Individuals who produced the signal to initiate grooming were likely to offer grooming. In contrast, during grooming bouts, groomers produced ELSs to request reciprocation of grooming from their partner. Our study demonstrates that chimpanzees do not ubiquitously use the ELS in a referential manner, but that they can use this gesture in a highly flexible fashion, with signal function depending on the intricate details of the social contexts in which they are produced.Publisher PDFPeer reviewe

Observational approaches to chimpanzee behavior in an African sanctuary: Implications for research, welfare, and capacity‐building

Research in African ape sanctuaries has emerged as an important context for our understanding of comparative cognition and behavior. While much of this work has focused on experimental studies of cognition, these animals semi-free-range in forest habitats and therefore can also provide important information about the behavior of primates in socioecologically-relevant naturalistic contexts. In this “New Approaches” article, we describe a project where we implemented a synthetic program of observational data collection at Ngamba Island Chimpanzee Sanctuary in Uganda, directly modeled after long-term data collection protocols at the Kibale Chimpanzee Project in Uganda, a wild chimpanzee field site. The foundation for this project was a strong partnership between sanctuary staff, field site staff, and external researchers. We describe how we developed a data-collection protocol through discussion and collaboration among these groups, and trained sanctuary caregivers to collect novel observational data using these protocols. We use these data as a case study to examine: (1) how behavioral observations in sanctuaries can inform primate welfare and care practices, such as by understanding aggression within the group; (2) how matched observational protocols across sites can inform our understanding of primate behavior across different contexts, including sex differences in social relationships; and (3) how more robust collaborations between foreign researchers and local partners can support capacity-building in primate range countries, along with mentoring and training students more broadly

The long lives of primates and the ‘invariant rate of ageing’ hypothesis

Is it possible to slow the rate of ageing, or do biological constraints limit its plasticity? We test the ‘invariant rate of ageing’ hypothesis, which posits that the rate of ageing is relatively fixed within species, with a collection of 39 human and nonhuman primate datasets across seven genera. We first recapitulate, in nonhuman primates, the highly regular relationship between life expectancy and lifespan equality seen in humans. We next demonstrate that variation in the rate of ageing within genera is orders of magnitude smaller than variation in pre-adult and age-independent mortality. Finally, we demonstrate that changes in the rate of ageing, but not other mortality parameters, produce striking, species-atypical changes in mortality patterns. Our results support the invariant rate of ageing hypothesis, implying biological constraints on how much the human rate of ageing can be slowed

Utilising Drone Technology in Primatology for 3D Mapping

Emergent Unmanned Aerial System (or drone) technology allows the 3-dimensional mapping of forest landscapes, allowing a new perspective of arboreal primate habitat use. Utilising UASs in primatological studies enables the assessment of habitat quality for different arboreal primate species, the identification of discreet forms of anthropogenic disturbance (such as historical selective logging), and detailed investigation of canopy use by arboreal primate species. Combining 3D canopy structure with microclimate measurements, we can see how canopy structure buffers solar radiation and how arboreal species may be affected by future climate change. We present data on a study of the arboreal primate community in a lowland section of the Gunung Leuser Ecosystem in northern Sumatra, focusing on how 3D canopy structure effects ranging (siamang, Symphalangus syndactylus), different primate species’ population densities (lar gibbon, Hylobates lar, siamang and Thomas langur, Presbytis thomasi) and habitat selection (orang-utan, Pongo abelii and siamang) and how UAS technology can be utilised in other future studies; the potential opportunities, challenges and pitfalls

The long lives of primates and the ‘invariant rate of ageing’ hypothesis

This work was supported by NIA P01AG031719 to J.W.V. and S.C.A., with additional support provided by the Max Planck Institute of Demographic Research and the Duke University Population Research Institute.Is it possible to slow the rate of ageing, or do biological constraints limit its plasticity? We test the ‘invariant rate of ageing’ hypothesis, which posits that the rate of ageing is relatively fixed within species, with a collection of 39 human and nonhuman primate datasets across seven genera. We first recapitulate, in nonhuman primates, the highly regular relationship between life expectancy and lifespan equality seen in humans. We next demonstrate that variation in the rate of ageing within genera is orders of magnitude smaller than variation in pre-adult and age-independent mortality. Finally, we demonstrate that changes in the rate of ageing, but not other mortality parameters, produce striking, species-atypical changes in mortality patterns. Our results support the invariant rate of ageing hypothesis, implying biological constraints on how much the human rate of ageing can be slowed.Publisher PDFPeer reviewe

Chimpanzee lip-smacking facilitates cooperative behaviour

Signalling plays an important role in facilitating and maintaining affiliative or cooperative interactions in social animals. Social grooming in primates is an example of an interaction that requires coordination between partners but little is known about communicative behaviours facilitating this activity. In this study, we analysed the communication of wild chimpanzees of Budongo Forest, Uganda, as they entered and maintained a naturally occurring cooperative interaction: social grooming. We found that lip-smacking, a distinct multimodal oral gesture produced during grooming, coordinated this activity. Lip-smacking at the beginning of grooming bouts was significantly more often followed by longer and reciprocated bouts than silent grooming initiations. Lip-smacks were more likely to be produced when the risk of termination of the interaction by the recipient was high, for instance when grooming vulnerable body parts. Groomers were also more likely to produce lip-smacks during face-to-face grooming where the visual aspect of the signal could be perceived. Data are consistent with the hypothesis that chimpanzee lip-smacks function to coordinate and prolong social grooming, suggesting that this oral signal is an example of a communicative behaviour facilitating cooperative behaviour in chimpanzees

Modeling Social Dominance: Elo-Ratings, Prior History, and the Intensity of Aggression

Among studies of social species, it is common practice to rank individuals using dyadic social dominance relationships. The Elo-rating method for achieving this is powerful and increasingly popular, particularly among studies of nonhuman primates, but suffers from two deficiencies that hamper its usefulness: an initial burn-in period during which the model is unreliable and an assumption that all win–loss interactions are equivalent in their influence on rank trajectories. Here, I present R code that addresses these deficiencies by incorporating two modifications to a previ- ously published function, testing this with data from a 9-mo observational study of social interactions among wild male chimpanzees (Pan troglodytes) in Uganda. I found that, unmodified, the R function failed to resolve a hierarchy, with the burn-in period spanning much of the study. Using the modified function, I incorporated both prior knowledge of dominance ranks and varying intensities of aggression. This effectively eliminated the burn-in period, generating rank trajectories that were consistent with the direction of pant-grunt vocalizations (an unambiguous demonstration of subordinacy) and field observations, as well as showing a clear relationship between rank and mating success. This function is likely to be particularly useful in studies that are short relative to the frequency of aggressive interactions, for longer-term data sets disrupted by periods of lower quality or missing data, and for projects investigating the relative importance of differing behaviors in driving changes in social dominance. This study highlights the need for caution when using Elo-ratings to model social dominance in nonhuman primates and other species

Quasi-periodic behaviour of Cyg X-3

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Wild chimpanzees (Pan troglodytes schweinfurthii) use tools to access out of reach water

The use of tools to drink water is well-documented in wild chimpanzees, but the specific function of this behavior is unclear. Here we use a large data set of drinking behaviors spanning 14 years of observation from the Kanyawara community of chimpanzees living in Kibale National Park, Uganda, to test two possible functions of leaf-sponges and other drinking tools. On the one hand, chimpanzees may use tools to access water that is hard to reach, which predicts that chimpanzees will preferentially use tools to drink at tree holes and crevices compared to all other locations. Conversely, chimpanzees may use these tools to filter stagnant water, in which case they would use tools more often at holes and puddles compared to running water sources (e.g., streams). We compared both likelihood of using a tool to drink at different locations, as well as overall rates of drinking, and found chimpanzees in this community most often drink from streams without tools. However, when they do use tools, they preferentially do so to drink at tree holes. Given known age and sex effects on tool use in chimpanzees, we also examined demographic variation in drinking tool use to understand the emergence of this behavior. While females use tools more often than males overall—in part driven by differences in drinking rates at different locations—both males and females use tools more frequently at tree holes than other locations when they do drink there. Finally, comparisons by age indicate that this selectivity strengthens over development with older chimpanzees showing a more pronounced effect of using tools more often at tree holes, suggesting that younger chimpanzees may exhibit exploratory tool use behavior. These results pinpoint the specific function of tool use during drinking and further suggest that even simple tools may require learning for use in appropriate contexts