Hadeda Ibis: See the Rainbow
22 February 2008 at Wildlife World Zoo
Contour feathers of Hadeda Ibis reflect light intensely at six distinct wavelengths ranging from near-ultraviolet (UV) to near infrared (IR), and up to four are within the range of visible (to humans) light, as reported by Brink and van der Berg (2004).
I am pleased that I am not the only one who has taken notice of this article!
A single layer of hollow melanosomes is observable, by Transmission Electron Microscopy (TEM), near the boundaries of the keratin cortex. Single-layer iridescence is produced by scattering of light from the surface of the barbule and the layer of hollowed melanosome platelets. The authors successfully matched the model to spectral reflectance data.
The keratin cortex of contour feathers of Hadeda Ibis is unusually thick ( ~0.8 µm), more than twice that reported for other birds exhibiting iridescent plumage. And while in most birds, the keratin cortex of feathers has been considered transparent, it was demonstrated that for Hadeda Ibis, the cortex absorbs in green to near-UV and exhibits anomalous dispersion in that range.
And authors noted that while many birds can visually detect UV reflectance peaks, they do not see in IR.