Our Invisible Violet Tinted World
Many birds, fish, reptiles, amphibians and insects can detect the violet and ultraviolet wavelengths in full daylight that are invisible to us humans. These animals have specialized cone cells in their retina that can detect lower frequencies of 300 nanometre (nm) wavelength (ultraviolet) while humans can only detect the 400 nm (purple) to 700 nm (red) spectra. They see the world with a violet tint.
The specialized cone cells of these animals have oil droplets in front of the visual pigment at the base of the cell. The oil droplets, which vary in size and number according to the spectra it is designed to detect, contain specific carotenoids that filter out different light frequencies. When oil droplets contain little carotenoid a full spectrum of light, including the UV wavelengths, flood through to the visual pigment. The light photons stimulate the pigment creating a cascade of biochemical reactions that depolarize optic nerves to register a colour in an animal’s brain. The signals from different cone cells reacting to UV, blue, green, or red spectra are consolidated in the animal’s brain to produce a tetrachromatic image of the world around them.
Read the full article UV World – MOSSAiC article.
UV perception by birds – Review – Rajchard et al 2009
UV function in birds – Cuthill et al 1999
Effect of selective removal of spectral bands – Zebra finches – Hunt et al 2001
Tetrachromacy , oil droplets bird plumage – Vorobyev et al 1998
UV vision in foraging vertebrates – Honkavaara et al 2002