Most extreme sexual dimorphism exhibited by parrot

Sexual dimorphism is the occurrence whereby the two sexes of a given species appear outwardly different in some way(s) from each other. The most extreme example of sexual dimorphism exhibited by any parrot species is that of the eclectus parrot Eclectus roratus, native to northeastern Australia, New Guinea, the Solomon Islands, and the Moluccas. For whereas the male's plumage is predominantly bright green, the female's is bright red with a bold blue-purple nape band. So dramatically different from one another are the female and male of this species in terms of their plumage's colour that until as recently as the early 1920s they were thought to constitute entirely separate species, rather than merely the two sexes of one and the same species.

The species is split into at least nine subspecies, each with its own distinct variations upon its plumage colour schemes, but the fundamental green male vs red-blue female plumage delineation is maintained in all of them.