Individual signature in the most common and context-independent call of the Rook (Corvus frugilegus)

Abstract

The ability to recognize other individuals (e.g., mates, neighbors, and offspring) is crucial to process relationships between group members in social species. For bird species with limited use of visual information, like species living in colonies or dense environments, the acoustic channel provides a long-distance and fast means to effectively convey identity-related information. The Rook (Corvus frugilegus) is a monogamous species, and one of the most social corvids, living in highly cohesive groups within colonies of hundreds to thousands of individuals. However, despite being a highly vocal species, only a few studies have focused on its acoustic communication skills, investigating mostly its vocal repertoire and kin recognition in fledglings. Among the vocal repertoire of the Rook, the “caw” is the most common sound type. It is emitted independently in various contexts and is often considered as a “presenting” vocalization, serving to introduce the identity of the emitter bird to the assembly. In this study, we investigated the potential individual signature of the caw. To do so, we recorded the caws of 5 semi-captive male Rooks and conducted acoustic analyses on both the frequency and time domains. A discriminant function and a potential for individuality coding analyses revealed the existence of a clear individual signature (mean of 75% correct classification, SD 10), which was mainly supported by the caw duration and distribution of energy in the low-frequency part of the spectrum. We discuss the potential variability of individuality coding across behavioral contexts and social affinities that needs further work.