The structure of an avian syllable syntax network

• We analyze the syllable association network in Troglodytes musculus songs.
• The network has small-world properties and non-random degree distribution.
• The syllable association network also presents a significant nested pattern.
• Results suggest the possibility of general principles for avian syntax networks.

A common result in recent linguistic studies on word association networks is that their topology can often be described by Zipf's law, in which most words have few associations, whereas a few words are highly connected. However, little is known about syntactic networks in more rudimentary communication systems, which could represent a window into the early stages of language evolution. In this study, we investigate the syntactic network formed by syllable associations in the song of the oscine bird Troglodytes musculus. We use methods recently developed in the context of the study of complex networks to assess topological characteristics in the syntactic networks of T. musculus. We found statistically significant evidence for nestedness in the syllable association network of T. musculus, indicating network organization around a core of commonly used notes, small-world features, and a non-random degree distribution. Our analyses suggest the possibility of a balance between the maintenance of core notes and the acquisition/loss of rare notes through both cultural drift and improvisation. These results underscore the usefulness of investigating communication networks of other animal species in uncovering the initial steps in the evolution of complex syntax networks.