Experimental evidence for compositional syntax in bird calls.

Toshitaka N Suzuki,David Wheatcroft,Michael Griesser

doi:10.1038/ncomms10986

Abstract

Human language can express limitless meanings from a finite set of words based on combinatorial rules (i.e., compositional syntax). Although animal vocalizations may be comprised of different basic elements (notes), it remains unknown whether compositional syntax has also evolved in animals. Here we report the first experimental evidence for compositional syntax in a wild animal species, the Japanese great tit (Parus minor). Tits have over ten different notes in their vocal repertoire and use them either solely or in combination with other notes. Experiments reveal that receivers extract different meanings from ‘ABC' (scan for danger) and ‘D' notes (approach the caller), and a compound meaning from ‘ABC–D' combinations. However, receivers rarely scan and approach when note ordering is artificially reversed (‘D–ABC'). Thus, compositional syntax is not unique to human language but may have evolved independently in animals as one of the basic mechanisms of information transmission.

Highlights

Human language can express limitless meanings from a finite set of words based on combinatorial rules
Putty-nosed monkeys (Cercopithecus nictitans) combine discrete alarm calls that denote different predator types to elicit group movements[16,17], but call receivers do not extract a compound meaning from the call combination[18]. It remains unknown whether animals have evolved compositional syntax or whether this is a unique feature of human language[6]
We investigated whether different note types produced by Japanese great tits (P. minor; Paridae) have distinct meanings to receivers when produced separately and, if so, whether receivers extract a compound meaning when both elements are combined

Summary

Introduction

Human language can express limitless meanings from a finite set of words based on combinatorial rules (i.e., compositional syntax). Putty-nosed monkeys (Cercopithecus nictitans) combine discrete alarm calls that denote different predator types to elicit group movements[16,17], but call receivers do not extract a compound meaning from the call combination[18] It remains unknown whether animals have evolved compositional syntax or whether this is a unique feature of human language[6]. Birds within the family Paridae produce structurally complex vocalizations (‘chicka’ or ‘chick-a-dee’ calls) that are composed out of different note types (for example, A, B, C and D)[19] Individuals use these calls in a range of contexts, such as to communicate the discovery of food sources[20,21], when approaching predators to deter them (i.e., mobbing)[22,23,24,25], or to maintain social cohesion with conspecifics[26,27]. D notes are both produced alone and in combination with other notes, suggesting that they modify the meaning of ABC calls to elicit appropriate mobbing responses to different predator types[25]

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Results

Conclusion