Trade-offs in the production of animal vocal sequences: insights from the structure of wild chimpanzee pant hoots

Abstract

BackgroundVocal sequences - utterances consisting of calls produced in close succession - are common phenomena in animal communication. While many studies have explored the adaptive benefits of producing such sequences, very little is known about how the costs and constraints involved in their production affect their form. Here, we investigated this issue in the chimpanzee (Pan troglodytes schweinfurthii) pant hoot, a long and structurally complex vocal sequence comprising four acoustically distinct phases – introduction, build-up, climax and let-down.ResultsWe found that in each of these phases, and for the sequence as a whole, there was a negative relationship between the number of calls produced and their average duration. There was also a negative relationship between the total duration of some adjacent phases. Significant relationships between the fundamental frequency of calls and their number or duration were found for some phases of the sequence, but the direction of these relationships differed between particular phases.ConclusionsThese results indicate that there are trade-offs in terms of signal duration at two levels in pant-hoot production: between call number and duration, and between the relative durations of successive phases. These trade-offs are likely to reflect biomechanical constraints on vocal sequence production. Phase-specific trade-offs also appear to occur between fundamental frequency and call number or duration, potentially reflecting that different phases of the sequence are associated with distinct types of information, linked in different ways to call pitch. Overall, this study highlights the important role of costs and constraints in shaping the temporal and acoustic structure of animal vocal sequences.Electronic supplementary materialThe online version of this article (10.1186/s12983-017-0235-8) contains supplementary material, which is available to authorized users.

Linguistic laws in chimpanzee gestural communication

“…R. Soc. B 286: 20182900 studies of human language and recently shown also to apply to vocal sequences of geladas [4] and chimpanzees [18], suggests that comparable principles of self-organization [48] underpin these different combinatorial communication systems. This law has not previously been explored in gestural communication in humans or other species; our results provide new evidence of an important commonality between human language and primate gestural communication, with respect to the basic structural patterns underpinning how signals are combined into larger structures.…”

“…This law has not previously been explored in gestural communication in humans or other species; our results provide new evidence of an important commonality between human language and primate gestural communication, with respect to the basic structural patterns underpinning how signals are combined into larger structures. In studies of this law in primate vocal communication [4,18], breathing-related constraints and energetic demands of vocal production were implicated as important drivers of the negative relationship between the number of calls in a sequence and their mean duration. Gestural sequences are not constrained by breathing patterns, as is the case for vocal sequences.…”

“…Menzerath's law predicts that 'the greater the whole, the smaller its constituents' and in language holds at different scales of analysis: in words with more syllables, the average syllable length is shorter [16], and in sentences with more clauses, the average clause length is shorter [17]. A negative relationship between construct and constituent size has been found in the vocal sequences of male geladas [4] and chimpanzees [18], and at the molecular level-between chromosome number and size across species [19], between exon number and size in genes [20], and between domain number and size in proteins [21].…”

The origins of gestures and language: history, current advances and proposed theories

“…Ninth, recent investigations of statistical regularities in primate vocal communication reveal patterns consistent with Zipf's law of abbreviation (i.e. frequently used words tend to become shorter) [Semple, Hsu & Agoramoorthy, ; Ferrer‐i‐Cancho et al ., ; but see Ferrer‐i‐Cancho & Hernández‐Fernández, for discussion about the law visibility] and with Menzerath's law (which predicts that longer sequences are made up of shorter constituents) (Gustison et al ., ; Fedurek, Zuberbühler & Semple, ; Gustison & Bergman, ) suggesting that common linguistic laws underlie the structure of vocal communication in human and non‐human primates.…”

Do penguins’ vocal sequences conform to linguistic laws?

“…More recently, the size of vocal sequences uttered by wild gelada males (Theropithecus gelada) was found to be negatively correlated with the duration of the calls constituting the sequences, providing the first indication of Menzerath-Altmann Law conformity in a non-human primate [2]. Evidence of conformity to Menzerath-Altmann Law also comes from Chimpanzee pant hoots [11]. However, more taxa remain to be investigated, especially beyond primates, to develop a broader understanding of the occurrence and significance of such statistical patterns in animal vocalizations.…”