The ‘Illusion’ of Green: How Color is Produced in Parrots

Green is the predominant wild type color among all Agapornis species.  It may give them the advantage in the wild, but in captivity, green is not the color of choice for most, as all color mutations were able to proliferate cause breeders have a free hand in choosing what color gene they want to propagate.  With a variety of color mutations across species particularly the roseicollis, fischeri and personatus, hobbyists have a hard time figuring out how these color mutations came about and how best to combine them.

Here is a familiar conversation: “After two clutches and seven progenies, my lutino and blue fischeri pairing yielded nothing but greens, while your green and green pairing has given you blue and a lutino, what is happening here?”  Similar conversations can be overheard every now and then in the lovebird community, feeling of exasperation for those stuck with progenies of the same color and excitement for those whose pair always yield some surprises.  However, we can understand these situations if we know how basic processes work and here we will learn how color is produced in parrots.

Green is not a color pigment in parrots in general or lovebirds in particular.  Yes, you heard it right, green is not a pigment in lovebirds. There are only two color pigments present in Agapornis – psittacin (also known as psittacofulvin) and eumelanin.  Psittacin is responsible for yellow, red, orange and pink while eumelanin gives us black to grey pigments.   We repeat, yellow, red, orange and pink are produced by the psittacin pigment, while eumelanin gives us shades of grey to black.  From here on in, serious lovebird breeders should take it to heart that there are only two color pigments in parrots in general and in lovebirds in particular – psittacin and eumelanin.  The importance of these terms in color production in parrots is not unlike learning to add and subtract in mathematics, as they always say, we should learn to crawl before we can learn to walk.

Let us dissect this one by one.  Psittacin is the pigment that gives yellow, red, orange and pink. Eumelanin is the pigment that provides black to grey coloration.  Fischeri’s head, for instance, has a red-orange to yellow coloration (psittacin) from forehead to the neck and its chest area, while the flight feathers are bluish black and its feet and nails are grey to black (eumelanin).

The big question: Where is green in the equation?  We made it clear that there is no green pigment and so far we have discussed that psittacin pigment gives us yellow, red, orange and pink, while eumelanin pigment expresses black to grey coloration.  How then do we account for green?

Structural color and the spongy zone.  Yes, the crucial component in most of the parrot feather’s structure that is responsible how green became possible is called the spongy zone (also known as the cloudy layer).  The spongy zone together with the two color pigments, psittacin, and eumelanin make possible the ‘illusion’ of green.   How?  We can only make sense of this if we are familiar with how the lovebird’s feather is structured.   In microscopic terms, the lovebird’s feather is composed of three components, first is the outer ring called the cortex, this is where the yellow psittacin pigment is located, second is the spongy zone situated in the middle and is largely made up of keratin is responsible for the structural color, third is the inner part we called medulla where the black eumelanin granules side by side with vacuoles can be found.

The cortex with yellow psittacin, the spongy zone in the middle and the black eumelanin granules and vacuoules in the medulla do not automatically result into green, we have to throw light in the equation and green appears almost like magic.  Natural light is composed of wavelengths that we can see (spectrum) and those that are invisible to our naked eye, the ultraviolet and infrared wavelengths.  We are only interested here to those that our eyes can see, the band of colors (rainbow colors) we call spectrum.  Light when dispersed through a prism produced the colors we see in a rainbow, i.e., red, orange, yellow, green, blue, indigo and violet.  The combination of these seven colors is what we see as white light.

When light first passes to the cortex where yellow psittacin is located, a small portion of the light is reflected but a large chunk continues to penetrate into the medulla where the black granules and the vacuoles (medullary cells composed mostly of air) are present.  We know that black absorbs all wavelengths, however, the vacuoles in the medulla caused some of these light to be reflected back into the spongy zone.  And this is where the structural color blue happens.  The spongy zone has a hollow tube-like nanostructure that made light reflect a blue color in a process experts calls constructive interference.  In other words, the blue color is reflected precisely because of the spongy zone’s structure and this is why blue is called a structural color.    The reflection outward of the structural color blue will then meet the yellow psittacin in the cortex, thereby, creating the optical ‘illusion’ green.   A simplified schematic diagram of a lovebird’s feather is presented below for more clarity.

Do you see any green or blue in the illustration?

Let us look at it again closely.  Light passes through the cortex where yellow psittacin is present, then to the spongy zone and then to the medulla where black granules should absorb light completely, however, the vacuoles side by side with the black granules reflected some of the light outwards.  Light traveling outwards then traverse the spongy zone where the structural color blue is then reflected.  Noticed that there are only two colors that were reflected back, the yellow psittacin and structural color blue.  What happens when yellow and blue were merged and were reflected directly to our eyes?  I guess we are all familiar with our art project at school when we are having fun mixing watercolors.  And what do we get when we mixed yellow with blue?  Absolutely, green.

This is how color is produced in parrots or lovebirds in particular.  You have two color pigments, psittacin and eumelanin and the spongy zone in between.  Psittacin yields yellow, red, orange and pink, while eumelanin takes care of the production of grey to black coloration.  Green is not a pigment.  Blue is also not a pigment. Green is produced through psittacin yellow and structural color blue through constructive interference involving the spongy zone.  It is imperative that serious hobbyists familiarize themselves how the interaction of these three components, psittacin, eumelanin and the spongy zone that made possible the production of the variety of colors we see in the Agapornis.  I assure you that this knowledge will come in handy when you are trying to understand the different kinds of mutations that we love to have in our aviaries.

References

  1. “Lovebirds Compendium” (2016), Dirk Van den Abeele.  The most comprehensive book in Agapornis so far written by a knowledgeable and experienced aviculturist.  This latest book of Dirk Van den Abeele will greatly satisfy your curiosity on all aspects of lovebird breeding particularly on color genetics.    This book is a must for all serious breeders who want accurate and insightful information from breeding to color mutations.
  2. “A Guide to Colour Mutations & Genetics in Parrots” (2002), Dr. Terry Martin BVSc.  For all bird lovers who want to understand the inner workings of how color is produced in the parrot world, this book is indispensable.  It will give you the basics then slowly make you understand that color mutations have similar effects among different species.
  3. Prum, R., Torres, R., Williamson, S., & Dyck, J. (1999). Two-Dimensional Fourier Analysis of the Spongy Medullary Keratin of Structurally Coloured Feather Barbs. Proceedings: Biological Sciences, 266(1414), 13-22. Retrieved from http://www.jstor.org/stable/51337

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