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Abstract The use of novel tools and technologies is transforming our approaches to study wild animal behaviour. Yet, from disturbance of natural habitats through field experiments to tagging, there is much ground for researchers to provide clear ethical assessment of their research practices and how they can affect wild animals. In this perspective, I review the current trends in field animal behaviour research, with a focus on studies on sociality, and investigate the forms under which such practices can impact animals. I focus particularly on the notions of disturbance and invasiveness. I build a parallel with the legal classifications in terms of degrees of severity found in the Swiss law and aimed at protecting animal well‐being, inspired by the principles of the 3R (Replace, Refine, Reduce) used in invasive animal research. I highlight how the impact of research can be assessed and monitored, particularly through behavioural and physiological means, identifying areas where such monitoring is critical, but also acknowledging the theoretical and practical limitations to such tools. I hope to trigger discussions on an ethical use of new tools and technologies, which can both inspire new research while limiting the disturbance to wild animals.

Whether one can label nonhuman primate signals as ‘meaningful’ hinges on what one takes as central features to meaning. If one targets a notion of meaning closely related and comparable to meaning in human words, two features must be identified: firstly, a concrete ascribable meaning to the signal and, secondly, an element of convention or arbitrariness of the signal’s meaning. In their seminal paper published in 1980, Seyfarth, Cheney and Marler demonstrated that vervet monkey alarm calls have concrete, discrete, ascribable meaning. But what about their arbitrariness? Here we will suggest a potential way into the investigation of this second feature: Human individuals are capable of comprehending arbitrary word meaning through learning and teaching processes. The current theory suggests in particular that imitation learning and natural pedagogy-like teaching behavior are necessary. For nonhuman primate signals, there is high doubt that learning processes are involved in the acquisition of novel signals, for instance, during ontogeny, and even higher doubt in the involvement of natural pedagogy. We will tackle the question of why complex imitation learning and natural pedagogy is not necessary for animal signals to be arbitrarily meaningful. We will also argue that the framework of ASL – Affective Social Learning – can help us determine whether simple forms of learning and passive forms of (indirect) teaching hinging on affective states of the teacher are involved, allowing for an arbitrary character of nonhuman signals.

Whether one can label nonhuman primate signals as ‘meaningful’ hinges on what one takes as central features to meaning. If one targets a notion of meaning closely related and comparable to meaning in human words, two features must be identified: firstly, a concrete ascribable meaning to the signal and, secondly, an element of convention or arbitrariness of the signal’s meaning. In their seminal paper published in 1980, Seyfarth, Cheney and Marler demonstrated that vervet monkey alarm calls have concrete, discrete, ascribable meaning. But what about their arbitrariness? Here we will suggest a potential way into the investigation of this second feature: Human individuals are capable of comprehending arbitrary word meaning through learning and teaching processes. The current theory suggests in particular that imitation learning and natural pedagogy-like teaching behavior are necessary. For nonhuman primate signals, there is high doubt that learning processes are involved in the acquisition of novel signals, for instance, during ontogeny, and even higher doubt in the involvement of natural pedagogy. We will tackle the question of why complex imitation learning and natural pedagogy is not necessary for animal signals to be arbitrarily meaningful. We will also argue that the framework of ASL – Affective Social Learning – can help us determine whether simple forms of learning and passive forms of (indirect) teaching hinging on affective states of the teacher are involved, allowing for an arbitrary character of nonhuman signals.

Children ‘overimitate’ causally irrelevant actions in experiments where both irrelevant and relevant actions involve a single common tool. This study design may make it harder for children to recognize the irrelevant actions, as the perceived functionality of the tool during the demonstration of the relevant action may be carried over to the irrelevant action, potentially increasing overimitation. Moreover, little is known how overimitation is affected by the demonstrator's expressed emotions and the child's prior success with the task. Here, 131 nine- to ten-year-old French and German children first engaged in a tool-based task, being successful or unsuccessful, and then watched an adult demonstrating the solution involving one irrelevant and one relevant action before smiling or remaining neutral. These actions were performed with the same tool or with two separate tools, testing potential carry-over effects of the functionality of the relevant action on the irrelevant action. We show that overimitation was higher when the same tool was used for both actions and when children were previously unsuccessful, but was not affected by the demonstrator's displayed emotion. Our results suggest that future overimitation research should account for the number of tools used in a demonstration and participants' previous task experience.

Functional Near-Infrared spectroscopy (fNIRS) is a neuroimaging tool that has been recently used in a variety of cognitive paradigms. Yet, it remains unclear whether fNIRS is suitable to study complex cognitive processes such as categorization or discrimination. Previously, functional imaging has suggested a role of both inferior frontal cortices in attentive decoding and cognitive evaluation of emotional cues in human vocalizations. Here, we extended paradigms used in functional magnetic resonance imaging (fMRI) to investigate the suitability of fNIRS to study frontal lateralization of human emotion vocalization processing during explicit and implicit categorization and discrimination using mini-blocks and event-related stimuli. Participants heard speech-like but semantically meaningless pseudowords spoken in various tones and evaluated them based on their emotional or linguistic content. Behaviorally, participants were faster to discriminate than to categorize; and processed the linguistic faster than the emotional content of stimuli. Interactions between condition (emotion/word), task (discrimination/categorization) and emotion content (anger, fear, neutral) influenced accuracy and reaction time. At the brain level, we found a modulation of the Oxy-Hb changes in IFG depending on condition, task, emotion and hemisphere (right or left), highlighting the involvement of the right hemisphere to process fear stimuli, and of both hemispheres to treat anger stimuli. Our results show that fNIRS is suitable to study vocal emotion evaluation, fostering its application to complex cognitive paradigms.

In comparative studies of evolution of communication, the function and use of animal quiet calls have typically been understudied, despite that these signals are presumably under selection like other vocalizations, such as alarm calls. Here, we examine vocalization diversification of chimpanzee quiet ‘hoos’ produced in three contexts—travel, rest and alert—and potential pressures promoting diversification. Previous playback and observational studies have suggested that the overarching function of chimpanzee hoos is to stay in contact with others, particularly bond partners. We conducted an acoustic analysis of hoos using audio recordings from wild chimpanzees (Pan troglodytes schweinfurthii) of Budongo Forest, Uganda. We identified three acoustically distinguishable, context-specific hoo variants. Each call variant requires specific responses from receivers to avoid breaking up the social unit. We propose that callers may achieve coordination by using acoustically distinguishable calls, advertising their own behavioural intentions. We conclude that natural selection has acted towards acoustically diversifying an inconspicuous, quiet vocalization, the chimpanzee hoo. This evolutionary process may have been favoured by the fact that signallers and recipients share the same goal, to maintain social cohesion, particularly among those who regularly cooperate, suggesting that call diversification has been favoured by the demands of cooperative activities.

Children are skilful at acquiring tool-using skills by faithfully copying relevant and irrelevant actions performed by others, but poor at innovating tools to solve problems. Five- to twelve-year-old urban French and rural Serbian children (N = 208) were exposed to a Hook task; a jar containing a reward in a bucket and a pipe cleaner as potential recovering tool material. In both countries, few children under the age of 10 made a hook from the pipe cleaner to retrieve the reward on their own. However, from five onward, the majority of unsuccessful children succeeded after seeing an adult model manufacturing a hook without completing the task. Additionally, a third of the children who observed a similar demonstration including an irrelevant action performed with a second object, a string, replicated this meaningless action. Children's difficulty with innovation and early capacity for overimitation thus do not depend on socio-economic background. Strikingly, we document a sex difference in overimitation across cultures, with boys engaging more in overimitation than girls, a finding that may result from differences regarding explorative tool-related behaviour. This male-biased sex effect sheds new light on our understanding of overimitation, and more generally, on how human tool culture evolved.

Ecological variation influences the appearance and maintenance of tool use in animals, either due to necessity or opportunity, but little is known about the relative importance of these two factors. Here, we combined long-term behavioural data on feeding and travelling with six years of field experiments in a wild chimpanzee community. In the experiments, subjects engaged with natural logs, which contained energetically valuable honey that was only accessible through tool use. Engagement with the experiment was highest after periods of low fruit availability involving more travel between food patches, while instances of actual tool-using were significantly influenced by prior travel effort only. Additionally, combining data from the main chimpanzee study communities across Africa supported this result, insofar as groups with larger travel efforts had larger tool repertoires. Travel thus appears to foster tool use in wild chimpanzees and may also have been a driving force in early hominin technological evolution.

Social network analysis methods have made it possible to test whether novel behaviors in animals spread through individual or social learning. To date, however, social network analysis of wild populations has been limited to static models that cannot precisely reflect the dynamics of learning, for instance, the impact of multiple observations across time. Here, we present a novel dynamic version of network analysis that is capable of capturing temporal aspects of acquisition--that is, how successive observations by an individual influence its acquisition of the novel behavior. We apply this model to studying the spread of two novel tool-use variants, "moss-sponging" and "leaf-sponge re-use," in the Sonso chimpanzee community of Budongo Forest, Uganda. Chimpanzees are widely considered the most "cultural" of all animal species, with 39 behaviors suspected as socially acquired, most of them in the domain of tool-use. The cultural hypothesis is supported by experimental data from captive chimpanzees and a range of observational data. However, for wild groups, there is still no direct experimental evidence for social learning, nor has there been any direct observation of social diffusion of behavioral innovations. Here, we tested both a static and a dynamic network model and found strong evidence that diffusion patterns of moss-sponging, but not leaf-sponge re-use, were significantly better explained by social than individual learning. The most conservative estimate of social transmission accounted for 85% of observed events, with an estimated 15-fold increase in learning rate for each time a novice observed an informed individual moss-sponging. We conclude that group-specific behavioral variants in wild chimpanzees can be socially learned, adding to the evidence that this prerequisite for culture originated in a common ancestor of great apes and humans, long before the advent of modern humans.

Chimpanzees and humans have co-existed in Africa for millennia. The forests inhabited by chimpanzees have experienced numerous changes in recent time, most notably during the last 12,000 years, as the current interglacial age started. In this article, I will study the case of Western Ugandan forests to describe the different factors, natural and human-induced, which affect a tropical forest, and draw hypotheses on the influence of these changes on chimpanzee cultural behaviour. Before colonial times, the Budongo Forest was shaped by elephant migrations and fires lit by the pastoralists who settled in the area. Later on, the British colonial power organized the exploitation of the forest through work plans aimed at insuring sustainable extraction of valuable timber. The human activity resulted in unexpected consequences in the forest. Interestingly, the resident chimpanzees are nowadays remarkable in the small size of their tool use repertoire. Ecological analysis and tool use observations in Uganda only support partly the opportunity and necessity hypotheses that are currently proposed to explain the influence of ecological factors on tool-using behaviour. Rather, the data I present here suggest that the temporal dimension of ecological changes in the forest must be taken into account to explain tool use behaviour variation in Ugandan forests. I propose a dynamic model connecting the necessity and opportunity factors influenced by ecological changes over time, most salient in Ugandan forests through the variability in food diversity. Finally, I conclude on the ever-changing ecological situation in Budongo Forest.

Joint travel is a common social activity of many group-living animals, which requires some degree of coordination, sometimes through communication signals. Here, we studied the use of an acoustically distinct vocalisation in chimpanzees, the 'travel hoo', a signal given specifically in the travel context. We were interested in how this call type was produced to coordinate travel, whether it was aimed at specific individuals and how recipients responded. We found that 'travel hoos' were regularly given prior to impending departures and that silent travel initiations were less successful in recruiting than vocal initiations. Other behaviours associated with departure were unrelated to recruitment, suggesting that 'travel hoos' facilitated joint travel. Crucially, 'travel hoos' were more often produced in the presence of allies than other individuals, with high rates of recruitment success. We discuss these findings as evidence for how motivation to perform a specific social activity can lead to the production of a vocal signal that qualifies as 'intentional' according to most definitions, suggesting that a key psychological component of human language may have already been present in the common ancestor of chimpanzees and humans.