Today is India’s 70th Republic Day and I thought what better animal to talk about today, than our National Bird – the Peacock.
Peacocks are renowned around the world for their immensely beautiful and supremely colourful tail feathers. For quite some time, it was assumed that peacocks derived their brilliant rainbow-like colours from plants; just like lots of other birds.
But recent research has revealed that the brilliant peacock tail feathers may actually be the result of light reflection, rather than the consumption of pigment-filled leaves, seeds and fruits.
Electromagnetic radiation is essentially a type of light. The electromagnetic spectrum is at its most basic, the distribution of this electromagnetic radiation or light. But not all of these light waves can be seen by the naked eye. The portion which we can see through the naked eye is called the visible light and we are able to see them, because of their specific wavelengths. The typical human eye can see electromagnetic waves that fall between 390 nanometres to 700 nanometres on the electromagnetic spectrum.
The feathers of a peacock contain structures called “photonic crystals”, which are bands of photons (photons = fundamental particles of light) that selectively reflect certain types of electromagnetic waves. When these waves fall within the visible light range of the spectrum, they can be seen by the human eye. The different colours that are visible on the peacock’s feathers are a result of waves of different lengths being reflected by the photonic crystals.
When light falls on the peacock’s feathers, the crystal lattice (the structural arrangement of the particles in crystals) in the photonic crystals, capture the light and reflect them in specific ways. The length of these reflected waves, then determine the colour of the peackock feather, plume and tail.
Research has found that peacock feathers get their colours when light is reflected off melanin-containing crystalline lattice rods that are spaced:
- Iridescent blues – 140 nanometres apart.
- Greens – 150 nanometres apart.
- Copper & Browns – 150-185 nanometres apart.
- Yellows – 165 nanometres apart.
- Other colours – from colour-mutations derived from blues and greens.
It isn’t just peacocks who possess photonic crystals in their feathers. Butterflies have them in their wings and chameleons have them on their skin.
Information about photonic crystals and their impact on animals is now being used by scientists to better-understand light and the role it plays in the animal kingdom.