Meaningful call combinations and compositional processing in the southern pied babbler

Abstract

Language's expressive power is largely attributable to its compositionality: meaningful words are combined into larger/higherorder structures with derived meaning. Despite its importance, little is known regarding the evolutionary origins and emergence of this syntactic ability. Although previous research has shown a rudimentary capability to combine meaningful calls in primates, because of a scarcity of comparative data, it is unclear to what extent analog forms might also exist outside of primates. Here, we address this ambiguity and provide evidence for rudimentary compositionality in the discrete vocal system of a social passerine, the pied babbler (Turdoides bicolor). Natural observations and predator presentations revealed that babblers produce acoustically distinct alert calls in response to close, low-urgency threats and recruitment calls when recruiting group members during locomotion. On encountering terrestrial predators, both vocalizations are combined into a "mobbing sequence," potentially to recruit group members in a dangerous situation. To investigate whether babblers process the sequence in a compositional way, we conducted systematic experiments, playing back the individual calls in isolation as well as naturally occurring and artificial sequences. Babblers reacted most strongly to mobbing sequence playbacks, showing a greater attentiveness and a quicker approach to the loudspeaker, compared with individual calls or control sequences. We conclude that the sequence constitutes a compositional structure, communicating information on both the context and the requested action. Our work supports previous research suggesting combinatoriality as a viable mechanism to increase communicative output and indicates that the ability to combine and process meaningful vocal structures, a basic syntax, may be more widespread than previously thought.call combination | compositionality | syntax | language evolution | southern pied babbler

Wild chimpanzees’ use of single and combined vocal and gestural signals

“…Siamese fighting fish: Doutrelant et al 2001; pied babblers: Engesser et al 2016; African elephants: Soltis et al 2005; see Smith 1965). Different cues may be detected by different audiences.…”

Formal monkey linguistics: The debate

“…This point should be borne in mind with respect to claims that some animal systems display aspects of compositionality. For instance, in an extremely interesting recent article, Engesser et al 2016 argue that pied babbler (Turdoides bicolor) display stronger reactions to an alert call followed by a series of recruitment calls (a combination they term a "mobbing sequence") than they do to either of their component parts (although the reactions are of the same types), and conclude that this communication system displays "rudimentary compositionality". But a crucial question is what one means by "rudimentary compositionality".…”

What Do Monkey Calls Mean?

“…This program could be extended to other systems of animal communication as well. [35]) properties, and we mentioned in our discussion of the Urgency Principle that they might be studied from a pragmatic perspective as well. In addition, it has been argued that birds can learn morphological patterns of affixation (involving prefixes and suffixes) in artificial languages ( [44]).…”

“…This explains why pyow-hack sequences are indicative of group movement; no idioms are posited, but competition principles are crucial (see [33] for a more detailed analysis). The Urgency Principle is speculative at this point, but it is noteworthy that it might explain some constraints on alert calls found in other species, notably in birds ([28][34] [35]). …”