In human color vision, a combination of yellow and blue pigments creates various shades of green, as the reflected wavelengths from the surfaces stimulate cone photoreceptors in the retina to varying degrees. So to our eyes, the xanthophyll pigment in the Blue and Gold Macaw’s head feathers that reflect yellow wavelengths combined with the air spaces in those same feathers that reflect blue wavelengths of light cause our eyes to see the feathers as green in bright light.
Abrupt changes in feather anatomy where some feathers deposit pigment and others have small air spaces with highly reflective particles in them create the color patterns in bird plumage. (Photo taken at Happy Hollow Park and Zoo in San Jose, CA)
But what does the bird see?
Birds have four types of cone photo-receptors (compared with the human three varieties), with the fourth type enabling them to detect much shorter wavelengths in the UV part of the spectrum.
There are striking differences between plumage coloration in UV light detected by birds and that seen by human photoreceptors in the visible part of our color spectrum. From: http://bucultureshock.com/imagination-ultraviolet-birds-part-3-of-4/.
Further, it appears that the coloration visible in the UV part of the spectrum may be of critical importance in signalling information about the fitness of an individual, just as the bright red coloration of a male cardinal signals its vigor and good health.
According to a new study from the University of York, Blue Tit mothers with bright blue patches on their head, strongly reflecting UV light, were better mothers and reared more offspring than females with duller (UV reflective) crowns.
Female Fairywrens (right) prefer the bright blue-bibbed males (left). These birds have shifted their visual sensitivity to the UV range by including more UV receptors in their retina. Study reported by researchers at Monash University (Melbourne) in 2012.
There’s a whole world of color out there that we are not able to see, and yet we make assumptions (and conclusions) about the various behaviors of birds and other animals, based on what we see. Makes you wonder what we’re missing.
What color are you really?