Over the Holidays my son gave us the book “Feathers” by Thor Hanson. Very interesting book! I was reminded that the feather color of birds derives from two different strategies: the nanostructure of the feather or colored pigments in the feather. In some cases both strategies work together – a yellow pigment below a structurally derived blue results in a lustrous green color in parrots, for example. I began to do further reading on feather color and then got distracted.
The May 2012 issue of “Scientific American” has an article entitled “Nature’s Color Tricks” that got me back on feather color again. What a fascinating subject. Structural colors result when light is reflected back from the surface of the feather by structures just a few nanometers (nanometer = one billionth of a meter) wide. The size and spacing of the structures order certain wavelengths of light, which are then perceived as specific colors. Depending on the shape of the nanostructure and the angle at which we see the feather, the color can abruptly change resulting in iridescence.
The tail feathers of the peacock provide an example of the variety of brilliant colors and iridescence created by nanostructures on a feather. Think of how different structural arrangements are necessary to produce the several colors in just the “eye” of the feather.
Peacock tail feathers are also iridescent. The color of the feather changes depending on the angle at which the feather is viewed. Looking up the peacock tail feather away from the body the color of the filaments is distinctly blue-green in bright sunlight.
Moving directly above the feather with the same light the filaments look more golden brown.
Again with the same light conditions, the filaments are copper brown looking toward the peacock’s body. This is iridescence as a result of changing the angle at which the nanoctructures on the feather are viewed. Of course, these delicate nanostructures cannot be seen with the naked eye or even regular microscopes.
If a peacock feather gets wet the colors disappear because the water causes a shift in the particular wavelength of light being reflected. That leads me to wonder about all the effort fly tyers go through to get exactly the right color feather for their fly. If the feather is one that reflects light, such as the much employed peacock tail feather, the color disappears when the fly gets wet anyhow.
Feather colors are intriguing – and I have not even pursued pigment based hues in this post. Some day. . .