Vocal communication in corvids: A systematic review

Vocal communication is broadly distributed in a wide range of nonhuman animal species and is hypothesized to play an important role in mate attraction, territory defence, predator avoidance and parental care. Understanding the ecological and social drivers of vocal communication is key to enhancing our understanding of the evolution of social structures, mating systems and group dynamics. We reviewed 130 studies investigating vocal communication in the family of corvids. As oscine passerines, living in complex and flexible social systems and a wide range of ecological systems (e.g. different habitats, trophic niches), corvids present a key model group in advancing our understanding of evolutionary drivers of vocal communication. Here, we outline empirical evidence for vocal learning, ecological adaptation (e.g. calls encoding information about predator type) and social adaptation (e.g. vocalizations for group cohesion and coordination) in corvid vocalizations and behavioural responses of receivers to calls. Only 35 out of 128 (27%) of corvid species have been studied with regards to their vocal communication. While some species, like American crows, common ravens and Eurasian magpies, are well studied, and supporting evidence for vocal learning and ecological as well as social adaptations is available, most corvid species remain poorly studied. We hope our review will inspire future work on previously underinvestigated corvid species, as well as replications of previous research with standardized observational and experimental paradigms, to allow for direct comparison between different corvid species. More broadly, further research systematically investigating social and ecological factors driving variation in vocal communication systems is necessary to further advance our general understanding of animal vocal communication.