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Associating with kin provides individual benefits but requires that these relationships be detectable. In humans, facial phenotype matching might help assess paternity; however, evidence for it is mixed. In chimpanzees, concealing visual cues of paternity may be beneficial due to their promiscuous mating system and the considerable risk of infanticide by males. On the other hand, detecting kin can also aid chimpanzees in avoiding inbreeding and in forming alliances that improve kin-mediated fitness. Although previous studies assessing relatedness based on facial resemblance in chimpanzees exist, they used images of captive populations in whom selection pressures and reproductive opportunities are controlled and only assessed maternity or paternity of adult offspring. In natural populations, the chances of infanticide are highest during early infancy, suggesting that young infants would benefit most from paternity concealment, whereas adults and subadults would benefit from the detection of all types of kin, including half-siblings. In our experiment, we conducted an online study with human participants, in which they had to assess the relatedness of chimpanzees based on facial similarity. To address previous methodological constraints, we used chimpanzee images across all ages, as well as maternal and paternal half-siblings. We found that kin status was detected above chance across all relatedness categories, with easier kin detection of father-offspring pairs, females, and older chimpanzees. Together, these findings support the existence of paternity confusion in infant chimpanzees and provide a possible mechanism for incest avoidance and kin-based social alliances in older individuals. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Social learning is of universal importance to animal life, and communication is likely to foster it. How do animals recognize when others produce actions that lead to relevant new information? To address this, we exposed 4 chimpanzees to an arbitrary learning task, a 2-choice visual discrimination paradigm presented on a touch screen that led to food reward. In each trial, images were paired with 1 of 4 acoustic treatments: (a) relevant or (b) irrelevant chimpanzee calls ("rough grunts" to food; "pant grunts" to a dominant conspecific), (c) a mechanical noise (hammer knocking sounds) and (d) silence. As we were interested in the effect of food calls on learning speed as compared to control stimuli, each chimpanzee was tested with the food call treatment, and 1 of the 3 control stimuli (either the pant grunt, mechanical noise, or silence condition). We found that learning was significantly enhanced in the contextually correct "rough grunt" condition, suggesting that food calls may play a role in the cultural transmission of food preferences, by priming individuals about a learning opportunity. We discuss these findings and propose that, at least in chimpanzees, the enhancing effect of these vocalizations may be related to the way they affect receivers' motivational/emotional and/or attentional systems. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Research has shown that great apes possess certain expectations about social regularities and both perceive and act according to social rules within their group. During natural and experimentally induced contexts, such as the inequitable distribution of resources, individuals also show protesting behaviors when their expectations about a social situation are violated. Despite broad interest in this topic, systematic research examining the nature of these expectations and the communicative signals individuals use to express them remains scant. Here, we addressed this by exploring whether bonobos (Pan paniscus) respond to violations of social expectations in naturally occurring social interactions, focusing on the vocal behavior of victims following socially expected and unexpected aggression. Expected aggression included conflicts over a contested resource and conflicts that were provoked by the victim. Unexpected aggression was any spontaneous, unprovoked hostility toward the victim. For each conflict, we also determined its severity and the composition of the nearby audience. We found that the acoustic and temporal structure of victim screams was individually distinct and varied significantly depending on whether or not aggression could be socially predicted. Certain acoustic parameters also varied as a function of conflict severity, but unlike social expectation, conflict severity did not discriminate scream acoustic structure overall. We found no effect of audience composition. We concluded that, beyond the physical nature of a conflict, bonobos possess certain social expectations about how they should be treated and will publicly protest with acoustically distinctive vocal signals if these expectations are violated., ((c) 2016 APA, all rights reserved).)

The influence of ecology on the development of behavioral traditions in animals is controversial, particularly for chimpanzees (Pan troglodytes), for which it is difficult to rule out environmental influences as a cause of widely observed community-specific behavioral differences. Here, we investigated 3 potential scenarios that could explain the natural variation in a key extractive tool behavior, "fluid-dip," among several communities of chimpanzees of the Pan troglodytes schweinfurthii subspecies in Uganda. We compared data from previous behavioral ecological studies, field experiments, and long-term records of chimpanzee tool-using behavior. We focused on the quality of the available food, dietary preferences, and tool sets of 5 different communities, and carried out a standardized field experiment to test systematically for the presence of fluid-dip in 4 of these communities. Our results revealed major differences in habitat, available diet, and tool use behavior between geographically close communities. However, these differences in ecology and feeding behavior failed to explain the differences in tool use across communities. We conclude that ecological variables may lead both to innovation and loss of behavioral traditions, while contributing little to their transmission within the community. Instead, as soon as a behavioral tradition is established, sociocognitive factors likely play a key maintenance role as long as the ecological conditions do not change sufficiently for the tradition to be abandoned.

Acoustic variability and individual distinctiveness of vocal signals are expected to vary with both their communicative function and the need for individual recognition during social interactions. So far, few attempts have been made to comparatively study these features across the different call types within a species' vocal repertoire. We collected recordings of the six most common call types from 14 red-capped mangabeys (Cercocebus torquatus) to assess intra- and interindividual acoustic variability, using a range of temporal and frequency parameters. Acoustic variability was highest in contact and threat calls, intermediate in food calls, and lowest in loud and alarm calls. Individual distinctiveness was high in contact, threat, loud and alarm calls, and low in food calls. In sum, calls mediating intragroup social interactions were structurally most variable and individually most distinctive, highlighting the key role that social factors must have played in the evolution of the vocal repertoire in this species. We discuss these findings in light of existing hypotheses of acoustic variability in primate vocal behavior.

Vervet monkey alarm calling has long been the paradigmatic example of how primates use vocalizations in response to predators. In vervets, there is a close and direct relationship between the production of distinct alarm vocalizations and the presence of distinct predator types. Recent fieldwork has however revealed the use of several additional alarm calling systems in primates. Here, the authors describe playback studies on the alarm call system of two colobine species, the King colobus (Colobus polykomos) of Taï Forest, Ivory Coast, and the Guereza colobus (C. guereza) of Budongo Forest, Uganda. Both species produce two basic alarm call types, snorts and acoustically variable roaring phrases, when confronted with leopards or crowned eagles. Neither call type is given exclusively to one predator, but the authors found strong regularities in call sequencing. Leopards typically elicited sequences consisting of a snort followed by few phrases, while eagles typically elicited sequences with no snorts and many phrases. The authors discuss how these call sequences have the potential to encode information at different levels, such as predator type, response-urgency, or the caller's imminent behavior., ((PsycINFO Database Record (c) 2009 APA, all rights reserved).)

Campbell's monkeys (Cercopithecus campbelli) frequently exchange vocalizations, the combined-harmonic calls, with individuals responding to one another's calls. Previous work has shown that these calls can be grouped into several structural variants. Adult females differ in their variant repertoires, which may change during their adult life, particularly after changes in the group composition. Playback of females' currently produced variants triggered vocal responses from other group members, whereas the same females' former, no longer used variants and those of stranger females never did. In contrast, former variants caused long-term cessation of vocal behavior, whereas stranger variants had no effect. Data showed that monkeys were able to distinguish between the different types of variants, indicating that these calls form part of a long-term social memory., (2005 APA, all rights reserved)

Some nonhuman primates have demonstrated the capacity to communicate about external objects or events, suggesting primate vocalizations can function as referential signals. However, there is little convincing evidence for functionally referential communication in any great ape species. Here, the authors demonstrate that wild chimpanzees (Pan troglodytes schweinfurthii) of Budongo forest, Uganda, give acoustically distinct screams during agonistic interactions depending on the role they play in a conflict. The authors analyzed the acoustic structure of screams of 14 individuals, in the role of both aggressor and victim. The authors found consistent differences in the acoustic structure of the screams, across individuals, depending on the social role the individual played during the conflict. The authors propose that these 2 distinct scream variants, produced by victims and aggressors during agonistic interactions, may be promising candidates for functioning as referential signals.