Social familiarity affects Diana monkey (Cercopithecus diana diana) alarm call responses in habitat-specific ways

The development of communication in alarm contexts in wild chimpanzees

ABSTRACT

Animals have evolved a range of communicative behaviours in the presence of danger. Although the mechanisms and functions of some of these behaviours have been relatively well researched, comparatively little is known about their ontogeny, including how animals learn to inform social partners about impending danger. In adult chimpanzees, behaviours in response to dangers involve several channels, particularly alarm calls and simultaneous gaze alternations with nearby recipients. Gaze alternations may allow inexperienced individuals to learn from more experienced ones by assessing their reactions to unfamiliar objects or events, but they may also provide the basis for more advanced social referencing. Here, we were interested in the development of these two common behaviours, alarm calling and gaze alternations, in wild chimpanzees (Pan troglodytes schweinfurthii) confronted with a threat. Using a cross-sectional design, we investigated those in 8 infant and 8 juveniles by experimentally exposing them to an unfamiliar but potentially dangerous object, a large, remotely controlled, moving spider model. For alarm calling, we found a positive relation with age, starting at around 28 months, although alarm calls were not consistently emitted until after 80 months. For gaze alternations, we found no age effect, with some of the youngest infants already showing the behaviour. Although its function remains unclear in infant and juvenile chimpanzees, gaze alternations emerge early in chimpanzee development. Alarm calling may require more advanced developmental stages, such as greater perceptual abilities, categorical capacities or more sophisticated social cognition, i.e. an understanding that danger is a collective experience that requires communication.

SIGNIFICANCE STATEMENT

Alarm calling and other anti-predatory behaviours have been the topic of much research but their ontogenies are still poorly described and understood. Recent studies on the behaviour of wild chimpanzees in threatening contexts have suggested sophisticated social cognitive abilities in adults. How do these behaviours develop in ontogeny? We addressed this question using a field experiment with 8 infants and 8 juveniles exposed to a novel and potentially threatening object in their natural habitat. We found that gaze alternations are present in some of the youngest individuals, potentially revealing early social awareness in chimpanzees. Age did not have an effect on the presence of gaze alternation. We also found that alarm calling was more common in older individuals, suggesting that call production and context of usage must be learnt. We discuss our results in light of developmental theories of social cognition and the role of social learning in the primate lineage.

Persistent Females and Compliant Males Coordinate Alarm Calling in Diana Monkeys

Sexual dimorphisms in animal vocal behavior have been successfully explained by sexual selection theory (e.g., mammals [1-5]; birds [6, 7]; anurans [8, 9]), but this does not usually include alarm calls, which are thought to be the product of kin or individual selection (e.g., [10, 11]). Here, we present the results of playback experiments with wild Diana monkeys, a species with highly dimorphic predator-specific alarms, to investigate the communication strategies of males and females during predator encounters. First, we simulated predator presence by broadcasting vocalizations of their main predators, leopards or eagles. We found that males only produced predator-specific alarms after the females had produced theirs, in response to which the females ceased alarm calling. In a second experiment, we created congruent and incongruent situations, so that the calls of a predator were followed by playbacks of male or female alarms with a matching or mismatching referent. For congruent conditions, results were the same as in the first experiment. For incongruent conditions, however, the males always gave predator-specific alarms that referentially matched the females' calls, regardless of the previously displayed predator. In contrast, females always gave predator-specific alarms that matched the predator type, regardless of their own male's subsequent calls. Moreover, the females persistently continued to alarm call until their own male produced calls with the matching referent. Results show that males and females attend to the informational content of each other's alarm calls but prioritize them differently relative to an experienced external event, a likely reflection of different underlying selection pressures.