I have sometimes wondered why it is that scarlet macaws (Ara macao, from South America) show the colours of the rainbow in order. That is, not only does this parrot have “all the colours of the rainbow” but they are in the same order on the body (or at least the wings) of the bird as the colours in a rainbow.
The order of the rainbow or visual spectrum (red, orange, yellow, green, blue).
Another parrot, the sun conure (Aratinga solstitialis, from South America) has a somewhat similar pattern of colours as the scarlet macaw, with the colours of the rainbow in rough order, with the reds, oranges and yellows at the top of the bird and the greens and blues on the wings. This conure is probably fairly closely related to the macaws.
Another South American conure (Aratinga jandaya) also shows plumage colours in the order of the rainbow:
The eastern rosella (Platycercus eximius), a bird common around here in Canberra, Australia, also has its coloured feathers moving in a fairly orderly way through the spectrum: red, orange, yellow, green, blue ..:
Below is a picture of the endangered Australian orange-bellied parrot (Neophema chrysogaster):
It also seems to have the same kind of colour order as the spectrum: … orange, yellow, green, blue … (moving upwards from the orange belly).
And another Australian parrot, the mulga parrot (Psephotus varius) also shows a hint of the same order ascending the bird’s body … red, orange, yellow, green? (turquoise?), blue …
Below is a picture of a parrot (the orange-fronted parakeet, Cyanoramphus malherbi, from New Zealand) which has been described as resembling a “flying rainbow”:
Another South American parrot, Hapalopsittica fuertesi, the indigo-winged parrot, with a suggestion of a sequence of yellow, green, blue and indigo.
It is hard to know if these “rainbow birds” just pop up in the parrot order randomly, or whether there is some unknown adaptive value in having the colours of the spectrum (in order) on their bodies. In any case, the effect occurs in a variety of parrot families and all around the world.
Two more “perfect rainbow parrots”:
Amazona oratrix (notice the colours in spectrum order on the wing):
And the extinct Carolina parakeet (Conuropsis carolinensis):