Substantial geographic variation, with three well-defined groups, each perhaps approaching separate species status: nigra group (with races livens and balzarensis), single-taxon caerulescens group, and gracilis group (including race flexipes); extensive intergradation, however, between nigra group and caerulescens. At other extreme, some authorities accept only two or three races. Six subspecies normally recognized.
Food and feeding
Status and conservation
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