Wild Birds Use an Ordering Rule to Decode Novel Call Sequences

Abstract

The generative power of human language depends on grammatical rules, such as word ordering, that allow us to produce and comprehend even novel combinations of words [1-3]. Several species of birds and mammals produce sequences of calls [4-6], and, like words in human sentences, their order may influence receiver responses [7]. However, it is unknown whether animals use call ordering to extract meaning from truly novel sequences. Here, we use a novel experimental approach to test this in a wild bird species, the Japanese tit (Parus minor). Japanese tits are attracted to mobbing a predator when they hear conspecific alert and recruitment calls ordered as alert-recruitment sequences [7]. They also approach in response to recruitment calls of heterospecific individuals in mixed-species flocks [8, 9]. Using experimental playbacks, we assess their responses to artificial sequences in which their own alert calls are combined into different orderings with heterospecific recruitment calls. We find that Japanese tits respond similarly to mixed-species alert-recruitment call sequences and to their own alert-recruitment sequences. Importantly, however, tits rarely respond to mixed-species sequences in which the call order is reversed. Thus, Japanese tits extract a compound meaning from novel call sequences using an ordering rule. These results demonstrate a new parallel between animal communication systems and human language, opening new avenues for exploring the evolution of ordering rules and compositionality in animal vocal sequences.

Syntax manipulation changes perception of mobbing call sequences across passerine species

“…They scan the environment when hearing the former and approach the sound source when hearing the latter. As previously seen in the Japanese tits (Suzuki et al, , ), these results indicate that these two motifs also convey distinct meanings to the great tit. One corresponds to an alarm call (i.e., the FME motif) which elicits increased vigilance from the receiver, while the other corresponds to a recruitment call (i.e., the D motif) which elicits approach behaviour from the receiver.…”

“…Both the nature and the intensity of the responses we observed in the present study are similar to those obtained for the Japanese tit (Suzuki et al, ) and for the pied babbler (Engesser et al, ). However, while in the Japanese tits both the vigilance effort and the propensity to approach vanish when tits hear the mobbing call sequence in the reversed order (Suzuki et al, , ), the results are different in the case of the great tit. The vigilance effort vanishes but the propensity to approach did not change when the combination order was reversed.…”

“…Our results also suggest that the combination order of the repetitive loud and broadband notes (i.e., the D motif) preceded by the frequency modulation notes (i.e., the FME motif) within the mobbing call sequence is of prime importance to elicit a response in the receiver. In this respect, it is particularly striking that, in the few bird species for which the effect of compositional syntax has been investigated, all studies reported that natural mobbing call sequences follow this combination ordering (Engesser et al, ; Suzuki et al, , ; Templeton et al, ). Furthermore, as suggested by the present study and recent studies on the Japanese tit (Suzuki et al, ), it seems that this rule is more important than the acoustic similarity of each motif between species to enable heterospecific response.…”

“…Although more and more evidence for syntax is becoming available for some birds and mammals (Coye, Ouattara, Zuberbühler, & Lemasson, ; Ouattara, Lemasson, & Zuberbühler, ), the ability of species to use compositional syntax (or compositionality; see Suzuki, Griesser, & Wheatcroft, ) is still debated (Bolhuis, Beckers, Huybregts, Berwick, & Everaert, ; Petkov & Jarvis, ; Petkov & Wilson, ; Suzuki, Wheatcroft, & Griesser, ). More recently, three studies have examined this issue by studying mobbing calls produced by the Japanese tit, Parus minor , and the southern pied babbler, Turdoides bicolor (Engesser, Ridley, & Townsend, ; Suzuki, Wheatcroft, & Griesser, , ). Mobbing calls are particular forms of alarm signals.…”

“…In the Japanese tit, each motif is also used alone in context other than mobbing. The FME motif is used in vigilance situations and it serves as an alarm signal to which receivers respond by scanning for danger (alert calls), while the D notes are involved within foraging flocks and by nestmates to recruit social partners and elicit an approach of the receivers (recruitment calls) (Suzuki, Wheatcroft, & Griesser, , ). When the Japanese tits heard the FME motif combined with the D notes as the compound FME‐D , which is also a natural vocalization, they showed both scanning and approach behaviours.…”