At the top of each peacock train feather, you'll see a round, jewel-toned ocellus or eyespot. Ocellus comes from the Latin word "oculus," which means "eye." These iridescent spots add the exotic dimension to the plumes.
Peacock tail feathers are specially structured to ensure that they reveal each brilliant ocellus whenever the bird fans them out. This is accomplished by combining multiple layers of feathers on top of each other, called upper-tail coverlets [source: National Zoo]. To the naked eye, the ocelli appear different shades of blues and greens, but in actuality, the feather fibers have a black pigment [source: Milius]. It's the different angles of the nanoparticles within those fibers that catch and reflect the sunlight to create iridescence [source: Milius].
In rare circumstances, peacocks may be born without any pigment. These albino peacocks are entirely white, although their feather structure remains the same. Even the ocelli are easily detectable.
According to Charles Darwin, the number and brilliance of those ocelli determine how successfully peacocks will attract peahens. Due to this form of sexual selection, he proposed that peacocks gradually evolved with more ornate trains to appeal to peahens.
During mating season, the males clump together in territorial groups called leks. Peahens will stroll through the leks, almost as though window-shopping for a new beau. To grab the females' attention, the peacocks will display their full regalia, stepping around excitedly and shaking their plumes. Ornithologists refer to that dating dance as shivering.
A recent study in Japan challenged the long-held belief behind the ornamentation of peacock trains, asserting that the more shake a peacock shows toward a peahen, the greater the likelihood of snagging her. Because of that interaction, the researchers theorized that it is perhaps this movement and mating calls -- not the famous ocelli -- that influence attraction the most [source: Viegas]. During a seven-year study of peafowl mating rituals, the researchers found that even the peacocks with the drabber fan and fewer ocelli hooked up as much as the showboats. But going up against Darwin isn't a simple feat. The scientific jury is still out on whether we can dismiss peacock ocelli's role with luring the ladies in.
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