INCONSISTENT GEOGRAPHIC VARIATION IN THE CALLS AND DUETS OF BARRED OWLS (STRIX VARIA) ACROSS AN AREA OF GENETIC INTROGRESSION

Much of our understanding of vocal geographic variation in birds is based on the dialects of oscine songbirds that learn their songs. Recent studies have revealed that nonoscine vocal behavior is more complex than previously thought, yet we still have a rudimentary understanding of how vocalizations of suboscine and nonpasserine birds are influenced by genetic and geographic variation. We examined geographic variation in male calls, female calls, and duets of Barred Owls (Strix varia) among 10 locations across the southeastern United States. Recent molecular work revealed two genetically distinct clades of Barred Owl at either end of our transect, with substantial introgression in between. We predicted that calls would vary with genetic distance in a clinal pattern, but that duets and duetting behavior might exhibit dialects similar to that of learned bird song. Discriminant analysis did not reveal any components of vocalizations or vocal behavior that could be used to assign vocalizations to the correct recording location. There were no relationships between any aspect of vocal structure or behavior and geographic distance. Some characteristics of male and female calls and duets varied among locations, but there was no discernible geographic pattern. We suggest that such inconsistent geographic variation in vocalizations is not unexpected for non-song-learning species. The lack of geographic pattern in vocalizations may be due, in part, to high levels of individual variation, recent signal evolution, and local adaptations. We discuss the application of these results to the ontogeny and evolution of complex, coordinated vocal behavior in nonpasserines. Received 23 September 2011, accepted 18 April 2012.