The light visible to our eyes is composed of many colors of light, each with its own distinct wave length. For example, red light has a long wavelength of around 700 nm, while blue light has a much shorter wavelength of around 400 nm. When light strikes an object, it either absorbs or reflects the various wavelengths. The particular wavelength or wavelengths reflected strike the retinas of our eyes and determines the color we perceive. When an object absorbs all wavelengths of light with none being reflected back, we perceive that object as being black. On the other hand, when an object reflects all wavelengths of light with none being absorbed, we perceive it as being white.
Most avian feather coloration is the result of different types of chemical compounds called pigments that are embedded in the feather during its development. The pigments absorb and reflect various wavelengths of light and thus determine the colors we see. The red of cardinals and the yellow of goldfinches are good examples of pigment color. Some species of birds, such as flamingoes, rely on carotinoids and other natural pigments obtained in their diet to maintain their color. When deprived of their natural diet of small planktonic crustaceans and algae, such as when they are kept in captivity, flamingoes lose their pink color and turn gray or dull buff, unless special formulas or artificial red dyes are added to their prepared food.
The blue coloration of most blue-colored birds such as bluebirds and white birds such as egrets is not from pigments but from structural coloration called schemochromes. This is a result of small changes in feather structure that alters their light reflective properties and results in a preferential scattering of light. Since blue light has a very short wavelength, it is selectively reflected more easily than other colors with longer wavelengths. If the red feather of a cardinal is ground to a powder, the color of the powder will be red due to the presence of red pigments. If you do the same thing with a blue feather from a bluebird, the powder will be dark instead of blue. Blue and green pigments are virtually unknown in birds except for the turaco family of Africa. The green coloration of most green birds is created by a combination of structural blue coloration and yellow carotinoid pigments in the feathers.
Iridescent colors, as seen in purple martins and grackles, is a physical phenomenon similar to structural blue color. Highly modified barbules on the feathers produce a differential reflection of wavelengths when they are rotated, so that a flat surface faces the incoming light. The structure of the barbules reflects some wavelengths of light and absorbs others, with the reflected wavelength changing with the angle of reflection. So as the bird moves around, the angle of reflection and wavelengths change, producing a change of color to the eye.
Blue is a very important color in the Bible, as it was chosen to represent the Ten Commandments. The color stands for truth and is where we get the term “true-blue.” The color blue was used in the sanctuary and was also worn as a ribbon of blue on the border fringes of the Israelites’ garments. This was a reminder for them to keep God’s Law. (See Numbers 15:38–40.) The color blue should still be important to us today as a reminder to keep God’s Ten Commandments! Even though a bluebird is truly not blue, the color we perceive from it is real and should remind us every time we see one that we are still obligated to keep God’s Law.
David Arbour writes from his home in DeQueen, Arkansas. He may be contacted by e-mail at: landmarks@stepstolife.org.