Element repetition rates encode functionally distinct information in pied babbler ‘clucks’ and ‘purrs’
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Human language is a recombinant system that achieves its productivity through the combination of a limited set of sounds. Research investigating the evolutionary origin of this generative capacity has generally focused on the capacity of non-human animals to combine different types of discrete sounds to encode new meaning, with less emphasis on meaning-differentiating mechanisms achieved through potentially simpler temporal modifications within a sequence of repeated sounds. Here we show that pied babblers (Turdoides bicolor) generate two functionally distinct vocalisations composed of the same sound type, which can only be distinguished by the number of repeated elements. Specifically, babblers produce extended ‘purrs’ composed of, on average, around 17 element repetitions when drawing young offspring to a food source and truncated ‘clucks’ composed of a fixed number of 2–3 elements when collectively mediating imminent changes in foraging site. We propose that meaning-differentiating temporal structuring might be a much more widespread combinatorial mechanism than currently recognised and is likely of particular value for species with limited vocal repertoires in order to increase their communicative output.
KeywordsElement repetition Temporal structure Animal communication Combinatoriality Language evolution Turdoides bicolor
We thank the Kalahari Research Trust, T. Clutton-Brock, M. Manser, the de Bruins and Kotzes for logistics and access to land; researchers and assistants at the Pied Babbler Project; R. Mundry for providing the R-pDFA script; M. Manser for support; and M. Manser, C. Bousquet, K. Bard and two anonymous reviewers for comments on previous versions.
Funding was provided by the Forschungskredit of the University of Zurich Grants 57191601 (to SE) and FK-14-077 (to SE), Swiss National Science Foundation Grants P1ZHP3_151648 (to SE), 31003A_153065 (to SWT), and PP00P3_163850 (to SWT), and the Claraz Stiftung (to SWT).
SE, ARR and SWT designed research; SE performed research and analysed data; SE and SWT wrote paper.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Permission was provided by the ethical committee for animal research of the University of Cape Town and the Northern Cape Conservation Authority, South Africa.
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