The development of communication in alarm contexts in wild chimpanzees

Guillaume Dezecache,Klaus Zuberbühler,Catherine Crockford

doi:10.1007/s00265-019-2716-6

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 statementAlarm 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.

Highlights

As a general rule, developmental patterns of anti-predatory behaviours appear to depend on a species’ life history, with rapidly maturing species showing fully functional behaviours earlier than slowly maturing ones (Lea and Blumstein 2011)
We found that gaze alternations are present in some of the youngest individuals, potentially revealing early social awareness in chimpanzees
Age had a positive effect on the likelihood of producing an alarm call (alarm call emission 7 of 8 juveniles (87.5%) vs. 2 of 8 infants (25%); see Table 1; likelihood ratio tests (LRT) χ2(1) = 5.24, P = 0.022) with individuals over 80 months more likely to emit alarm calls than younger individuals (Fig. 3)

Summary

Introduction

Developmental patterns of anti-predatory behaviours appear to depend on a species’ life history, with rapidly maturing species showing fully functional behaviours earlier than slowly maturing ones (Lea and Blumstein 2011). Infants learn to ignore events that do not pose a direct threat and will eventually only alarm call to a small range of dangerous predator species (Seyfarth and Cheney 1980). This developmental process is adaptive insofar as it enables individuals to develop habitat-specific anti-predator responses, whilst reducing the likelihood of costly false positives (Owings and Loughry 1985; Lea and Blumstein 2011). Gradual changes in alarm call usage during infancy have been reported in meerkats (Suricata suricatta) (Hollén and Manser 2006; Hollén et al 2008), an alternative developmental model suggests that age-related differences in alarm calling behaviour reflect age differences in susceptibility to predation rather than individual experience (Hollén et al 2008; Hollen and Radford 2009; Lea and Blumstein 2011)

Methods

Results

Discussion

Conclusion