Data from: Internal acoustic structuring in pied babbler recruitment cries specifies the form of recruitment

Language is inherently combinatorial, and parallels of this combinatorial capacity are found in nonhuman systems, with animals combining sounds and calls into larger meaningful structures. However, further analogue examples are central in unveiling the diversity, distribution, and evolutionary drivers of combinatoriality. Here, we provide evidence for internal “meaning-refining” acoustic variation within a larger stereotyped signal in pied babblers (Turdoides bicolor). Using acoustic analyses, we demonstrate that males produce 2 long, raucous, “cry-like” structures, both starting with a wind-up segment grading into repetitions of A/single-note or AB/double-note motifs. Behavioral observations indicated that, consistent with similarities in their larger stereotyped structure, both variants function overall in recruiting group members during locomotion, but the internal A or AB substructure specifies the “precise” form of recruitment, from approaching the caller’s announced location to following it over longer distances. Playing back cries from a stationary loudspeaker further supported that the 2 variants elicit different responses, with more individuals approaching the loudspeaker in response to single-note compared with double-note cries. Additionally, despite similarities in overall distance travelled, group movement was only directional for single-note, but undefined for double-note cries. We suggest that the overall structure of the 2 cry variants conveys the same general meaning, with embedded variation refining this meaning. These results further illustrate the variability of generative mechanisms outside of human language and lend support to the hypothesis that combinatorial structuring may have emerged in species with limited or fixed vocal repertoires in order to enhance communicative output.,Engesser et al 2018_Supporting datasetEngesser_et_al_Pied-RecruitmentCries_Dataset.xlsx,

语言本质上具备组合性，这类组合能力的类似现象在非人类系统中亦有体现：动物可将声音与鸣叫声组合为具有更大意义的结构。然而，更多类似案例是揭示组合性（combinatoriality）的多样性、分布模式与演化驱动因素的核心关键。本研究在斑鸫鹛（*Turdoides bicolor*）的定型化大信号（stereotyped signal）中，发现了内部可"细化含义"的声学变异（acoustic variation），并提供了相关证据。通过声学分析（acoustic analyses），我们证实雄性斑鸫鹛会发出两种长而沙哑的"cry-like"结构：二者均以起始铺垫段（wind-up segment）起头，随后逐步过渡为A/单音节或AB/双音节模式（motifs）的重复序列。行为观测（behavioral observations）表明，尽管两种变体的整体定型化结构相似，二者的核心功能均为在移动过程中召集群体成员，但内部的A或AB子结构则明确了召集的“精准形式”：从前往呼叫者宣告的位置，到跟随其进行长距离移动。通过固定扬声器播放鸣叫声的实验进一步证实，两种变体可引发不同的行为反应：相较于双音节鸣叫声，单音节鸣叫声能吸引更多个体靠近扬声器。此外，尽管群体移动的总距离无显著差异，但单音节鸣叫声可引发具有方向性的群体移动，而双音节鸣叫声则未引发明确的定向移动。我们据此提出，两种鸣叫变体的整体结构传递相同的通用含义，而内嵌的声学变异则对该含义进行细化。本研究结果进一步阐明了人类语言之外的组合生成机制的多样性，并为以下假说提供了支持：当物种的鸣唱曲目（vocal repertoires）有限或固定时，为提升传播效率，其可能演化出组合式结构（combinatorial structuring）。本研究使用的辅助数据集为Engesser等人2018年发布的Engesser_et_al_Pied-RecruitmentCries_Dataset.xlsx