merely a pigment of the imagination – part 1

European Starling
(Wikipedia)

I recently was asked to design some birds for a mural here in Shreveport to be painted by the public. I got to pick which birds, and made my list of Passerines that are local, attractive, colorful, recognizable, and easily translatable to paint-by-numbers. I was zooming through the designs, recommending Pantones with excitement until I crashed into a little brick wall called the European Starling.

People are attracted to bright colors. Butterflies, beetles, amphibians, and of course birds bear colors that span from Roy to G. Biv. You and I are sadly not as colorful (though current trends on Pinterest are trying their hardest to change that – somebody stop the madness).  We're all pretty much shades of brown and blacks, and when lined up on a spectrum, really don't show that much variation from one person to the next.

So melanin-y. (Wikipedia)

We’re colored primarily via pigments called melanins. Our two primary types of melanins are eumelanin (blacks and browns) and pheomelanin (reddish browns). The infinite combinations of quantities of eumelanins and pheomaelanins comprise the spectrum of human coloration, spanning from skin to hair to eye color and characterize mammalian coloration. Birds also utilize melanins, as is finely exemplified by the Red-tailed Hawk to the right.

Reds, oranges, and yellows also are results of pigments. Carotenoids are the family of pigments that give animals these beautiful fire colors and, as a rule, cannot be manufactured by animals’ cells. Instead, they have to acquire them from the environment via diet. Cue back to the amazing story about Cedar Waxwing’s tail tips turning orange due to the consumption of both yellow and red honeysuckle berries, and flamingos being pink dependent on their consumption of crustaceans in their shallow wading pools.

Though not as common, another coloration mechanism exists in birds. Pigments called porphyrins are identifiable by their fluorescence when exposed to ultraviolet light. Unlike melanins or carotenoids, which are lipids (fats), porphyrins are modified amino acids and can reflect back greens, brilliant reds, pinks and even browns when exposed to white light. In fact, I noticed a few years back when working with a Barred Owl that it had a soft pink tinge to the underside of its wings. After some research, I discovered that that pink tinge was due to the presence of porphyrins in owl plumage. Had I shown a UV light on that owl, it would have lit up like a Christmas tree (read the paper here).

So what about blues? Where do they come from? And why couldn’t I draw that European Starling? These questions lead us into a whole different box of cookies called structural coloration – a mechanism of producing color without a pigment. Blue, and the colors of an iridescent surface like a European Starling, do not exist as physical entities within feathers. No molecule or "thing" exists within feathers that is actually blue-colored or iridescent-colored. In fact, one might say such colors are merely pigments of the imagination...

Hold your bated breath. Part two on structural coloration headed your way.

TEASER. (Wikipedia)