EPOW - Ecology Picture of the Week

Emerald Dove (Chalcophaps indica); Northern Queensland, Australia.
Natural light (left); camera flash (middle); computer-enhanced color (right).

Explanation:   Look closely at the wing of this Emerald Dove in the Australian tropics.  Does the wing seem to change color?  First, it's green, then brown, then mottled more brightly.  So what color is it, really?

It is all these colors... under different light.  The left photo is in natural light, the middle photo is with a bright camera flash, and the right photo is enhanced on the computer to increase the contrast among colors.  

Feathers of birds can display colors in two ways, by pigmentation and by reflectance or iridescence.  Pigmentation means that colored pigments are inherently part of the feathers' structure, and generally do not change color under different lighting situations or viewing angles.  Iridescence, however, depends on the quality of light and often the viewing angle.  Many birds use iridescence, including blackbirds, starlings, ibises, and others.  

Blue or green feathers are nearly always produced by iridescence.  And iridescence can produce multi-color effects under natural light when viewed the right way.  However, Emerald Doves always appear with uniform green wings.  So, why would they have developed wings with multicolor mottling that cannot be seen?  

Maybe a better question is, how do Emerald Doves view each other?  Can they see the variation in colors that we humans cannot with our unaided eyes? If so, then what is the function of these color patterns?  Perhaps they serve to entice mates or announce social structure or territories...?  If only we saw through the eyes of a dove.