Dolphin communication : a quantitative linguistics approach

Comparative studies between human languages and animal communication have revealed shared statistical patterns that can shed light on the principles that govern communication across species while establishing the foundations to understand the evolution and the origin of languages. Two linguistic laws - Menzerath's law and Zipf's law of abbreviation - provide the framework to study the shared principle of information compression. Menzerath's law states that the longer the construct, the shorter its consistent parts, while Zipf's law posits a negative correlation between signal length and frequency of use. These statistical patterns are found in complex behaviours across diverse taxa, suggesting that the principle of compression is universal in animal communication. Here, we investigate whether the whistle of dolphins (Tursiops truncatus), a species widely known for its outstanding communication and social skills, conform with these linguistic laws. We show that, in dolphin vocal sequences, there is a negative relationship between the number and the duration of whistles, in line with Menzerath's law. Furthermore, based on an unsupervised whistle type classification, we find patterns that are consistent with Zipf's law of abbreviation in the relationship between the duration of a whistle type and its frequency of use. These findings provide evidence for coding efficiency in the vocal communication system of this species and for the first time among cetaceans. Finally, our results suggest that compression underpins human and dolphin vocal communication, illustrating the importance of recent extensions of information theory and also the need of exploring linguistic laws beyond human vocal systems