STRUCTURAL COLOUR: STAR SPECIES NUMBER 4
Special Power: Non-fading Colours
The Eurasian Jay (Garrulus glandarius) is a beautiful, medium-sized, colourful and noisy bird that belongs to the crow family – the Corvidae. It is easy to identify thanks to the bright blue wing patch. The current scientific name is from Latin: Garrulus means noisy or chattering, and glandarius is “of acorns”, a favourite food.
Scientists from the University of Sheffield have used X-rays to study the blue and white feathers of the Jay and have found that these birds use well-controlled changes to the nanostructure* of their feathers to create the vivid colours of their plumage.
They are able to control the pattern of different colours along an individual feather barb – the equivalent to having many different colours along a single human hair. Instead of pigments that would fade over time, Jays use well-controlled changes to the nanostructure to create their vividly coloured feathers. It is thought that the birds use this feature to recognise one another.
The Jay’s feather, which goes from ultra violet in colour through to blue and into white, is made of a nanostructured spongy keratin material, the same that human hair and fingernails are made from. The researchers found that the Jay is able to demonstrate amazing control over the size of the holes in this sponge-like structure and fix them at very particular sizes, determining the colour that we see reflected from the feather. When light hits the feather the size of these holes determines how the light is scattered and the colour that is reflected. As a result, larger holes mean a broader wavelength reflectance of light, which creates the colour white, and smaller holes with a more compact structure, result in the colour blue.
If the colours were formed using pigments created from the bird’s diet, the feather colour would fade over time. However, since nature has developed a way to create the colours through structural changes, any nanostructure will remain intact, explaining why birds never go grey as they age. In contrast, humans rely on pigments to colour hair and because these are not produced to the same extent as we age, we consequently go grey.
*A nanostructure is a structure of intermediate size between microscopic and molecular structures.