Biology subjects

Hobaiter, C.

Publications and source records attributed to Hobaiter, C..

14 recordsLinked to original sources

bioRxiv2026

Wild chimpanzees in Bugoma Forest, Uganda follow the Ugandan feeding ecology etiquette but exhibit cultural singularities: a case for the cultural junction hypothesis

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.

animal behavior and cognition↗

bioRxiv2025

Testing methodological and population-specific influences on the detection of Zipf's law of brevity in chimpanzee gestures

Zipfs law of brevity is a widespread manifestation of information compression found across human languages and other communication systems. Chimpanzee gesture represents a rare absence of its expression in short-range communication. But, whether this absence reflects a feature of ape gesture production, or results from methodological obstacles or population differences is unclear. Selecting the appropriate unit of analysis is crucial for detecting linguistic patterns in any system. We assess gestural repertoires of three chimpanzee communities for Zipfs law, while discriminating and testing different levels of unit durations (segmentation) and how finely gestural units are split (granularity). We report the first repertoire-wide detection of Zipfs law in ape gesture in one chimpanzee community at a specific level of segmentation and granularity. We suggest that both methodological and socio-ecological factors can shape the detection and expression of Zipfs law, emphasizing the importance of species-relevant units and metrics for meaningful cross-species comparisons.

animal behavior and cognition↗

bioRxiv2025

Chimpanzee culture beyond the conspicuous: Evidence for broad-scale observational social learning in wild individuals

Wild chimpanzees possess diverse cultural repertoires, representing the richest example of non-human animal cultures. However, traditional methods, which investigate culture at the group level, have likely underestimated the full extent of chimpanzee cultural repertoires. In particular, the cultural relevance of everyday behaviors has remained largely unexplored. Here, we investigated evidence for social transmission of everyday behaviors to assess the breadth of individuals cultural repertoires in a population of wild eastern chimpanzees (Pan troglodytes schweinfurthii). First, we validated whether peering (i.e. close-range observation of a conspecific) serves as an indicator of social (i.e., cultural) learning. We then examined the contexts in which chimpanzees engage in peering to determine the range of behaviors that may be culturally transmitted. Finally, we explored potential motivations and additional functions of peering behavior. Our results indicate that chimpanzees use peering for targeted social information seeking in learning-intensive contexts. Peering rate was highest during immaturity, for complex or rare food items, and when observing older, more experienced conspecifics. Overall, wild chimpanzees peered at a wide range of everyday skills, such as feeding and grooming, and directed peering towards various conspecifics from an early age. We found no evidence supporting peering as a begging or submissive "gesture", but our findings indicate that it may function as a signal to initiate affinitive interactions. Our findings suggest that wild chimpanzees use peering to learn a broad variety of skills, thereby highlighting unrecognized cultural potential in everyday skills. Furthermore, our findings suggest that peering may have multiple functions and underlying motivations.

animal behavior and cognition↗

bioRxiv2025

Toxoplasma in a natural population of chimpanzees

Toxoplasma gondii is a unicellular parasite that can infect most warm-blooded animals. In humans, it is linked to schizophrenia and other neurological disorders. It is also responsible for congenital toxoplasmosis, which can be lethal or cause severe neurological damage in the developing foetus. More subtle behavioural effects have been observed in various species, including humans, in particular increased risk-taking, which is thought to increase the parasites transmission to feline predators, the definitive hosts. We investigated the prevalence of Toxoplasma gondii in wild eastern chimpanzees (Pan troglodytes schweinfurthii) in the Budongo Forest, Uganda. We tested 45 individuals of two communities, one of which (Sonso) has a home range overlapping with human settlements. In this community, the prevalence was 22.7% (N=5 of 22), whereas in the neighbouring, but more isolated, Waibira community none of the 23 individuals tested were infected. The majority of infected Sonso individuals were adult males and/or high-ranking group members, attributes associated with increased risk-taking behaviour in chimpanzees and other animals. While further work is necessary to reveal the causal relation between infection and behaviour, our findings open new avenues of research for the neural impact of parasites on primate social behaviour.

zoology↗

bioRxiv2024

Sex differences in pant-hoot vocalizations in wild Eastern chimpanzees

Chimpanzee pant-hoots are frequently produced long-distance vocalisations that serve a number of social functions, such as to indicate coordinate travelling, food discovery, or social status. Calling often triggers replies by others, offering potential for some form of group-level decision-making through vocal exchanges. However, despite important physiological and social differences between male and female chimpanzees, pant-hoot research has traditionally focused on males, with very little known about female use. To address this gap, we collected all-occurrence behavioural data from wild adult female and male Eastern chimpanzees (Pan troglodytes schweinfurthii) in two communities in the Budongo Forest Reserve, Uganda. We show that females pant-hooted regularly, but less frequently than males and, when they did so, mostly in response to others. Response pant- hoots were more common than initiating pant-hoots in both sexes (females: 90.1%; males: 69.5%), and male and female chimpanzees responded to pant-hoots heard at a similar rate (females: 14.1%, males excluding alpha: 15.8%). Both sexes were more likely to respond to pant-hoots from within their own party, but this effect was stronger for females. The likelihood of male chimpanzees pant-hooting in response was inhibited in larger party sizes, while females response pant-hoots were not. Finally, female response pant-hoots were less common during periods of maximal oestrous as compared to other stages of their reproductive cycle. Overall, our findings demonstrate that response pant-hoots are subject to social factors, such as within-sex social competition and between-sex reproductive strategies, which affect male and female chimpanzees in different ways, a further demonstration of the high degree of audience awareness in this primate species. HighlightsO_LIChimpanzees use pant-hoots in both sex-specific and sex-non-specific ways C_LIO_LIIndividual and social factors impact likelihood of pant-hoot production C_LIO_LIOur findings suggest pant-hoots are important flexible elements of vocal behaviour for male and female chimpanzees. C_LI

animal behavior and cognition↗

bioRxiv2024

Old age variably impacts chimpanzee engagement and efficiency in stone tool use

We know vanishingly little about how long-lived apes experience senescence in the wild, particularly with respect to their foraging behaviors, which are essential for survival. Some wild apes use tools during foraging and, given the additional cognitive and physical challenges presented by tool use, we predict that such behaviors are at a heightened risk of senescence. However, until the present, longitudinal analysis of the effects of progressive aging on wild ape tool-use behaviors has not been possible due to a lack of available data. In response to this research gap, we sampled data from a longitudinal video archive that contained footage of wild chimpanzees engaging in one of their most complex forms of tool use - the cracking of hard-shelled nuts with hammers and anvil stones, termed nut cracking - at an outdoor laboratory at Bossou, Guinea. By sampling data over a 17-year period, we describe how the extent to which wild chimpanzees engage in - and efficiently perform - nut cracking changes between the ages of approximately 39-44 to 56-61 years of age. Over this extended sampling period, chimpanzees began attending experimental nut cracking sites less frequently than younger individuals. Several elderly chimpanzees exhibited reductions in efficiency across multiple components of nut cracking, including taking more time to select stone tools prior to use, and taking longer to crack open nuts and consume the associated pieces of kernel. Two chimpanzees also began using less streamlined behavioral sequences to crack nuts, including a greater number of actions (such as more numerous strikes of the hammer stone). Most notably, we report interindividual variability in the extent to which elderly chimpanzees tool-use behaviors changed during our sample period - ranging from small to profound reductions in tool engagement and efficiency - as well as differences in the specific aspects of nut cracking behaviors that changed for each individual as they aged. We discuss the possible causes of these changes with reference to research into senescence in captive primates, and provide future directions for research of primate aging in both captive and wild settings.

animal behavior and cognition↗

bioRxiv2024

Predictability of next elements in chimpanzee gesture sequences

Recent research has produced evidence for basic combinatorial abilities in the vocal systems of different animal species. Here, we investigate the structure of gesture sequences in Eastern chimpanzees (Pan troglodytes schweinfurthii) to detect whether gestural communication shows non-random combinations and how combinatorial rules influence predictability. Gesture, as compared to vocalization, offers greater flexibility in how signals are combined--for example overlapping in time -- and as the parsing of signals into sequences is dependent on researcher decisions, we employ a multiverse approach, considering four different definitions of what constitutes a sequence based on varying time thresholds. Our results indicate that sequences tend to be short (even with the most liberal time-window) and that transitions between some gesture types occur more frequently than expected by chance, with some transitions showing significant association across all time-windows. These transitions often involve repetition, suggesting persistence as a key aspect of chimpanzee gestural sequences. Information about previous gestures reduced uncertainty in predicting subsequent gestures. The order of gestures within sequences appears to be less critical than their cooccurrence, challenging assumptions based on the linear patterning derived from vocal communication. Our findings highlight the importance of methodological choices in sequence definition and suggest that chimpanzee gestural communication is characterised by a mix of predictability and flexibility, with implications for understanding the evolution of complex communication systems.

animal behavior and cognition↗

bioRxiv2023

Many morphs: parsing gesture signals from the noise

Parsing signals from noise is a general problem for signallers and recipients, as well as for researchers studying communicative systems. Substantial research efforts have been invested in comparing how other species encode information and meaning in their signals, and how signalling is structured. However, our ability to do so depends on identifying and discriminating signals that represent meaningful units of analysis. Early approaches to defining signal repertoires applied top- down approaches, classifying cases into predefined signal types. Recently, more labour-intensive methods have taken a bottom-up approach describing the features of each signal in detail and clustering cases into types based on patterns of similarity between them in multi-dimensional feature-space that were previously undetectable. Nevertheless, it remains essential to assess whether the resulting repertoires are composed of relevant units from the perspective of the species using them, and redefining repertoires when additional data makes more detailed analyses feasible. In this paper we provide a framework that takes data from the largest set of wild chimpanzee (Pan troglodytes) gestures currently available, splitting gesture types at a fine scale based on modifying features of gesture expression and then determining whether this splitting process increases the information content of the communication system. Our method allows different features of interest to be incorporated into the splitting process, providing substantial future flexibility across - for example - species, populations, and levels of signal granularity. In doing so we provide a powerful tool allowing researchers interested in gestural communication to establish repertoires of relevant units for subsequent analyses within and between systems of communication.

animal behavior and cognition↗

bioRxiv2022

Habitual ground nesting in the Bugoma Forest chimpanzees (Pan troglodytes schweinfurthii), Uganda.

We report the presence of habitual ground nesting in a newly studied East African chimpanzee (Pan troglodytes schweinfurthii) population in the Bugoma Central Forest Reserve, Uganda. Across a 2-year period we encountered 891 night-nests, 189 of which were classified as ground nests, a rate of [~]21%. We find no preliminary evidence of socio-ecological factors that would promote its use and highlight local factors, such as high incidence of forest disturbance due to poaching and logging, which appear to make its use disadvantageous. While further study is required to establish whether this behaviour meets the strict criteria for non-human animal culture, we support the argument that the wider use of population and group-specific behavioural repertoires in flagship species, such as chimpanzees, offers a tool to promote the urgent conservation action needed to protect threatened ecosystems, including the Bugoma forest.

ecology↗

bioRxiv2021

Dead infant carrying by chimpanzee mothers in the Budongo Forest

It has been suggested that non-human primates can respond to deceased conspecifics in ways that suggest they experience psychological states not unlike humans, some of which could indicate they exhibit a notion of death. Here, we report long-term demographic data from two East African chimpanzee groups. During a combined 40-year observation period we recorded 191 births of which 68 died in infancy, mostly within the first year. We documented the post-mortem behaviour of the mothers and describe nine occasions where Budongo chimpanzee mothers carried infants for 1-3 days after their death, usually until the body started to decompose. We also observed three additional cases of extended carrying lasting for more than two weeks, one of which was followed by the unusual extended carrying of an object and another which lasted three months. In each case, the corpses mummified. In addition, we report four instances of recurring dead infant carrying by mothers, three of whom carried the corpse for longer during the second instance. We discuss these observations in view of functional hypotheses of dead infant carrying in primates and the potential proximate mechanisms involved in this behaviour.

animal behavior and cognition↗

bioRxiv2021

Flexibility in the social structure of male chimpanzees (Pan troglodytes schweinfurthii) in the Budongo Forest, Uganda

Individuals of social species face a trade-off between the competitive costs and social benefits of group living. Species show a range of social strategies to deal with this trade-off, for example atomistic fission-fusion dynamics in which temporary social groups of varying size and membership form and re-form; or molecular fission-fusion dynamics which contain stable sets of multilevel nested subgroups. Chimpanzees are considered an archetypical atomistic fission-fusion species, using dynamic changes in day-to-day association to moderate the costs of within-group competition. It has been argued that humans highly flexible social organisation allows us to live in extremely large groups. Using four years of association data from two neighbouring communities of East African chimpanzees (Pan troglodytes schweinfurthii), we describe new levels of flexibility in chimpanzee social organisation and confirm the presence of subgrouping in a second, large community of chimpanzees. We show that males from the larger Waibira community (N males 24-31) exhibited additional levels of semi-stable subgrouping, while males from the smaller Sonso community (N males 10-13) did not. Subgroup membership showed stability across some years, but flexibility across others. Our data support the hypothesis that chimpanzees can incorporate strategies other than fission-fusion to overcome costs of social living, and that their social organisation may be closer to that of modern humans than previously described. SIGNIFICANCE STATEMENTSocial living offers benefits and costs; groups can more easily locate and defend resources, but experience increased individual competition. Many species, or individuals, flexibly adjust their social organization when faced with different competitive pressures. It is argued that humans are unique among primates in combining multigroup social organisation with fission-fusion dynamics flexibly within and across groups, and that doing so allows us to live in extremely large groups. Using four-years of association data we show new levels of flexibility in chimpanzee social organization. Males from a typically-sized community employed atomistic fission-fusion dynamics, but males in an unusually large community incorporated additional semi-stable levels of subgrouping. Our data support the hypothesis that chimpanzee males combine social organization strategies, and that doing so may allow them, like humans, to mitigate individual costs at larger community sizes.

animal behavior and cognition↗

bioRxiv2021

Non-genetic maternal effects shape individual differences in cortisol phenotypes in wild chimpanzees

Glucocorticoids, such as cortisol, mediate homeostatic processes, allowing individuals to adjust to fluctuating environments. The regulation of circadian cortisol responses, a key homeostatic function, has been shown to be heritable. However, to understand better the role of parental care in shaping physiological functioning in long-lived mammals with protracted parental care, there is a need to disentangle genetic and non-genetic parental contributions to variation in glucocorticoid phenotypes. We used a dataset of 6,123 cortisol measures from urine samples from 170 wild chimpanzees spanning 18 years of data collection. We found consistent inter-individual differences in circadian cortisol phenotypes, with differences most apparent when considering average cortisol levels given the effect of time of day. Maternal effects explained around 10% (2-18%) variation in these average cortisol levels, while variation attributable to genetic factors was not distinguishable from zero. Our results indicate, relative to genetic effects, a qualitatively stronger influence of mothers, whether via epigenetic processes or via behavioral priming for coping with stressors, in shaping cortisol phenotypes in this species. This provides novel insight into the vital role of mothers in the developmental plasticity of long-lived mammals and, more generally, the selective pressures shaping physiological plasticity.

zoology↗

bioRxiv2021

Linguistic laws are not the law in chimpanzee sexual solicitation gestures.

Two language laws have been identified as consistent patterns shaping animal behaviour, both acting on the organisational level of communicative systems. Zipfs law of brevity describes a negative relationship between behavioural length and frequency. Menzeraths law defines a negative correlation between the number of behaviours in a sequence and average length of the behaviour composing it. Both laws have been linked with the information-theoretic principle of compression, which tends to minimise code length. We investigated their presence in a case study of male chimpanzee sexual solicitation gesture. We failed to find evidence supporting Zipfs law of brevity, but solicitation gestures followed Menzeraths law: longer sequences had shorter average gesture duration. Our results extend previous findings suggesting gesturing may be limited by individual energetic constraints. However, such patterns may only emerge in sufficiently-large datasets. Chimpanzee gestural repertoires do not appear to manifest a consistent principle of compression previously described in many other close-range systems of communication. Importantly, the same signallers and signals were previously shown to adhere to these laws in subsets of the repertoire when used in play; highlighting that, in addition to selection on the signal repertoire, ape gestural expression appears shaped by factors in the immediate socio-ecological context.

animal behavior and cognition↗

bioRxiv2019

Ecological and dietary differences between Ugandan chimpanzee communities with possible implications on tool use

Some East African chimpanzee (Pan troglodytes schweinfurthii) communities, such as the Sonso chimpanzees, display an unusually limited range of tool-use, but it remains unclear whether this is due to ecological and/or cultural factors. Information on ecological conditions and the diet of the Sonso chimpanzees in relation to neighbouring communities is needed. Here, we studied three adjacent communities in Budongo Forest (Sonso, Waibira, and Kamira), and the presumed core area of an undescribed community (Mwera), in the neighbouring Bugoma Forest. Through line-transects, we investigated (i) whether there were differences in food diversity and abundance between the communities home ranges; (ii) whether the home ranges differed in abundance of sticks and insect nests; and (iii) whether Sonso and Mwera chimpanzees differed in their diet (using faecal samples). Across communities, Sonso had the richest food availability and the lowest insect nest abundance. However, food availability in Mwera, Bugoma, was richer than Budongo communities that neighbour the Sonso territory, suggesting that there may be variation within Budongo. Data from faecal samples replicated our direct observations of food availability suggesting that Sonso chimpanzees had a broader diet than Mwera chimpanzees. This difference in foods availability may partially explain the Sonso chimpanzees lack of stick-tool-use, and low levels of insectivory. The tool repertoire of the other communities is currently unknown; however, we make predictions based on our ecological data. More detailed knowledge of small-scale variation in ecology within and between forest habitats may be important to advancing our understanding of the drivers of tool-use.\n\nSIGNIFICANCE STATEMENT - HIGHLIGHTED STUDENT PAPERTo advance our knowledge of the role of ecological factors in the emergence of tool use in chimpanzees, a nuanced understanding of the ecological conditions different chimpanzee communities experience is needed. We studied four Ugandan chimpanzee communities in two forests. One of these communities, Sonso, in the Budongo Forest, is well-known for its restricted range of tool types, including a total absence of stick use. Food diversity and abundance were highest, and stick tool use opportunities (abundance of sticks and insect nests) were lowest for the core-habitat of the Sonso chimpanzees in contrast to the other communities. We argue that ecological factors play a role in their unusual pattern of tool use, and make predictions about the expected types of tool use in the other communities based on their ecology. Thus, our study provides information that may help advance our understanding of how tool use arises under varied socioecological circumstances.

ecology↗