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www.thevillagenews.co.za
20 May 2020
MY ENVIRONMENT
Birds of a dazzling feather By Anina Lee
of their kind, especially during mating season. Colour is so important to birds that they have evolved a whole host of ways to paint their feathers. Let’s look at how some of the different hues come about.
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ver since I owned a pet Rainbow Lorikeet, I have been fascinated by the colours of birds. Apart from their magnificent looks, lorikeets are also highly intelligent, as are all parrots. But that’s another story. Across the world, tribal peoples have used the plumes of the birds they hunted to decorate themselves. Feathers have been a sign of status in western societies too. Birds flaunt a variety of eye-catching plumage and we are amazed at the vibrant colours every time we see a flashy bird. But have you ever stopped to think about how and why these creatures get to be so dazzling? From peacock blue through swan white to oriole orange, every bird colour is produced by the interaction of just two colouring systems – one structural and one chemical. Structural colour results from the scattering of reflected light, while chemical colour relies on a palette of pigments. Intricately arranged feather layers allow chemistry and structure to interact to produce the colours we see. Birds rely on their coloration and feathers to communicate with others
Dark colour If you love the dark black of a crow or the brown stripes of an owl, you can thank melanin. This is the same substance that provides colour to our own skin and hair and is also responsible for the darker colours on birds. Melanins produce black feathers, but depending on the concentration of the pigment granules, they can also range to reddish browns and pale yellows. These colours are especially prevalent on birds’ flight feathers – for good reason. Melanin is very strong, and allows the hardest-working feathers to better resist wear and tear. That not only allows the bird to remain in tip-top shape, but also to be more aerodynamic. Warm colours Bright red, yellow and orange feathers are produced by carotenoids. These pigments can also interact with melanins to produce even more colours, such as olive green. There are more than 600 types of carotenoids. However, birds cannot make their own carotenoids. Carotenoids are produced by plants, and are acquired by eating plants or by eating something that has eaten a plant.
This, for example, is how flamingos come to be pink. Newly hatched chicks are grey and have to accumulate their carotenoids second-hand, from shrimp and other crustaceans. Carotenoids are also seen in songbirds, but tend to be rare among game birds. This is not surprising as game birds rely on good camouflage rather than eye-catching colour. Porphyrins Porphyrins, the third pigment group, are complex organic compounds formed from amino acids. Porphyrins come in a wide range of colours, including brown, pink, red and green. Certain birds, such as parrots, get their bright colours from these less-common pigments produced directly in their feathers. Porphyrins are only found in a scant handful of birds. In 1868, it was discovered that the red feathers of Turacos are coloured by a pigment that was named turacin, after the turaco birds that contain this porphyrin. Turacin is about 7 percent copper, which is why it gives off such a blinding red hue. A similar pigment called turacoverdin provides green coloration. Iridescence Cool colours like blues and iridescence come from micro-structures in feathers. We are familiar with the bright iridescence of sunbirds. The iridescent microstructures are made of keratin. Keratin is the structural protein of human nails, rhinoceros horns, whale baleen, turtle shells, pangolin scales, and of course, bird
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feathers. Keratin is also responsible for the iridescent colouring of many spectacular bird species. Keratin produces colour in two main ways: by layering and by scattering. Layering colours are produced when translucent keratin reflects short wavelengths of colours like blues, violets, purples and greens. The other colours are absorbed by an underlying melanin (black) layer. The ways in which the keratin of the feathers are layered will dictate the colour of the iridescence. Examples of layered colouring include the iridescence of glossy starlings and the speculums or wing patches of many duck species. Scattering is produced when the keratin of feathers is interspersed with tiny air pockets within the structure of the feathers themselves. These air pockets and the interspersed keratin scatter blue and green light and produce the shimmering colours of birds like kingfishers, rollers and bee-eaters. Because blue light has very short wavelengths, it is reflected more easily than other colours of light with longer wavelengths. This was first understood in 1869, when scientist John Tyndall noted that minuscule particles in earth’s atmosphere (later identified as mainly nitrogen and oxygen) preferentially scattered blue light, resulting in the familiar ‘sky blue’ of a clear summer day. Blue plumage colour is often referred to as a ‘Tyndall blue’ structural colour. 3
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In essence, keratin allows feathers to act like a prism by scattering the longer wavelengths of light and reflecting shorter ones to emit gorgeous blues, violets, purples, and greens. Mixing reflected blue light with underlying yellow carotenoids makes green feathers. Bird make-up Some animals ‘paint’ themselves with so-called cosmetic colours from resources available in their surroundings. For example, the bearded vulture or ‘lammergeyer’, is a species known for its bright orange underside, neck, and head. The birds acquire the colouring by dusting their feathers with iron oxide-rich red soils. No one knows why the vultures use ‘make-up’, though it's evident that the ruddiest ones get the most respect. If the brilliant colours of bird feathers help to gain respect in the avian world, it’s little wonder that humans, especially those in power, like to follow suit and adorn themselves in royal colours such as blue, red and purple. For an excellent visual explanation of the chemistry of bird colours, go to YouTube and search "Why Are Birds Different Colors?" Birds with magnificently colourful plumage include the: 1. Knysna Turaco PHOTO: Chris Peterson 2. Lilac Breasted Roller PHOTO: Ted Schifferman Photography 3. Rainbow Lorikeet PHOTO: Wikimedia Commons
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4. Malachite Kingfisher PHOTO: Timeless Africa Safaris
