Do bats' social vocalizations conform to Zipf's law and the Menzerath-Altmann law?

The study of vocal communication in non-human animals can uncover the roots of human languages. Recent studies of language have focused on two linguistic laws: Zipf's law and the Menzerath-Altmann law. However, whether bats' social vocalizations follow these linguistic laws, especially Menzerath's law, has largely been unexplored. Here, we used Asian particolored bats, Vespertilio sinensis, to examine whether aggressive vocalizations conform to Zipf's and Menzerath's laws. Aggressive vocalizations of V. sinensis adhere to Zipf's law, with the most frequent syllables being the shortest in duration. There was a negative association between the syllable number within a call and the average syllable duration, in agreement with Menzerath's law. A decrease in the proportion of some long syllables and a decrease in the duration of several syllable types in long-duration calls explain the occurrence of this law. Our results indicate that a general compression principle organizes aspects of bat vocal communication systems.