Out of the blue: geographic variation and divergence between Azure Jays (Cyanocorax caeruleus) from two ecologically distinct ranges

ABSTRACT Underlying biological processes can often shape phenotypic variation. Although subtle, the variation in plumage colour of the Azure Jay (Cyanocorax caeruleus) has long been suggested to be of phylogeographic importance, but this hypothesis was not tested. This species’ distribution in the Atlantic Forest biome of south-eastern Brazil is divided into two ecologically distinct portions by the Serra do Mar mountain line. The availability of Parana Pine (Araucaria angustifolia) seeds is essential for the survival of Azure Jays in the western range but not in the eastern range. Here we quantify Azure Jay geographic variation using three datasets, including vocalisations, morphology and plumage colour. All available data independently supported the hypothesis of divergence between east and west. Azure Jays in the western range tend to have: (1) larger body dimensions, (2) vocalisations with lower pitch and entropy, and (3) a greenish-blue plumage, than those in the eastern range. Based on the available data on this species’ ecology, life history and sociality, we discuss how features from the western range could indicate specialisation in habitat use. We discuss potential links between our results and the past of the Atlantic Forest and the implications for this species conservation in a highly threatened habitat. Finally, we highlight the pressing need for demographic and molecular evidence to make data-oriented and effective decisions for this species conservation.