Kingfishers are not blue!
— Wildlife Sightings (@wildlife_uk) August 22, 2014
I know what you are thinking. She’s gone mad, of course Kingfishers are blue, we have pictures by the hundred on twitter of blue Kingfishers. That’s how you recognise a Kingfisher IT’S BLUE!
Sadly however, for many people’s sanity and peace of mind, Kingfisher’s feathers are not actually that lovely turquoise blue we are so familiar with, they are really a murky brown. Remove them from sunlight and the feathers are actually brown.
The colour we see and associate with everyone’s favourite fisher is actually a product of physics. I know, everyone is pressing the back button as I speak, but this really is quite interesting and makes you look at these lovely birds in a whole new light (forgive the pun).
There is no blue pigment in the feathers of a Kingfisher. The blue is a result of structural colouration. The structure of the feathers (which are made up of sponge like keratin like our hair and nails) scatters blue light by a process called the Tyndall effect. Visible white light is made up of loads of different colours of light (remember the song “Sing a rainbow”). Blue light has a shorter wavelength compared to the other colours (except Violet), at about 400 nano meters. This fact means that blue light is more easily reflected by particles in the feathers back towards our eyes (since light is reflected when it strikes a particle of equal or greater diameter to it’s wavelength). All the other colours pass straight through. This reflected blue light reaches our eyes and leads to us perceiving the familiar blue of the bird. Incidentally this is the same process by which we see the sky as blue.
This colouration is not the result of iridescence, as it is in the colours on Hummingbirds etcetera. We can tell this because the Kingfisher still appears blue no matter what angle it is viewed from, whereas Hummingbird throat patches, for instance, produced by iridescence appear and disappear depending on the viewing angle.
So the next time you catch a glimpse of blue darting past you. Or you marvel at a beautiful Kingfisher perched on a branch. Remember it’s not blue. It’s brown!
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