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Monday, July 04, 2005

Rainbow effects in parrots' plumage

I have sometimes wondered why it is that scarlet macaws 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 of the bird as the colours in a rainbow. It suggests some kind of structural cause for the coloration rather than individual pigments that just happen to be present in the bird's plumage in the order of a rainbow: red, orange, yellow, green, blue ...

This paper "The Chemical Structure of the Pigments in Ara macao Plumage" by Stradi et al. suggests that something structural is indeed going on. A quote: " We expect to demonstrate that the brilliant colors of the parrot plumage are principally due to such interactions, and that parrots construct their rainbow of color simply by modulating the interaction of a few endogenous yellow pigments with the plumage keratin. " That is, there may be a single basic pigment that is converted "structurally" to produce other colours. What is interesting is that the structural modulation seems to vary in such a way that the plumage shades change in the same order as a rainbow, at least in the case of Ara macao, the scarlet macaw.

I noticed today, at the Canberra Zoo and Aquarium, that the sun conure (another parrot) 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.

ADDENDUM 16 March 2012: I don't know why I didn't point out here before that 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, indigo, violet:

Eastern rosella

On the other hand, despite its name, the rainbow lorikeet (Trichoglossus haematodus) has its colours of the rainbow in no particular order:

Rainbow lorikeet


Julian

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