This Turkey Tuesday is about the stunning array of colors and tones that toms display on their feathers. These brilliant colors are actually caused by light refracting off feathers, rather than feather colors. Crystals within the feathers block certain wavelengths of light but allow others to pass, which essentially controls the intensity of colors that we see. Further, iridescence, which is the phenomenon where a surface appears to change colors as the angle of view changes, creates the brilliant shine that makes toms so stunning. Iridescence is an important part of breeding displays used by toms, because not only does it attract attention from hens, it also provides information to the hens sizing up a particular tom. Research in the 1990s showed that toms with high parasite loads have less ultra-violet light reflection and less iridescence on their feathers. In other words, they don’t “look” as good as toms with lower parasite loads, which suggests that hens may be able to assess iridescence and use it to determine the health and fitness of a tom. The tom in this picture taken by Joe Foster is showing incredible brilliance of color and iridescence, to the point that his feathers glow. The take home is, the stunning colors and iridescence we enjoy when watching toms is an important part of the display toms use, and help hens determine the fittest toms in the breeding population.