How Do Birds Get Their Colours?
Birds are some of the most colourful animals in the world. But where do those colours actually come from? Today we dive into the four sources for the brilliant spectrum of birds.
EPISODE NOTES
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TRANSCRIPT
Birds come in an absolute kaleidoscope of colours - that’s one reason birdwatching has an edge on, say, squirrel watching.
But have you ever wondered how they pull off such a stunning spectrum? Where does that kaleidoscope actually come from? In fact it takes a combination of four sources, and today we’re going to take a tour through all of them.
Three of those four are pigments, and the first is melanin. It’s found in just about every animal - it’s what darkens our skin when we get a tan, for example. It’s produced by melanogenesis in specialized cells called melanocytes.
Melanin is a multipurpose protein, but as a pigment it’s responsible for darker colours like black or earth tones. You can see it in crows, sparrows, hawks, and the non-red parts of a red-winged blackbird.
The second kind of pigments are the carotenoid family. Carotenoids are warm-toned pigments and give us the brilliant crimson of the northern cardinal and the striking yellow of the American goldfinch and yellow warbler.
But what’s crazy is, none of those birds can produce carotenoid pigments. They can only get them from what they eat, often plants, where they’re essential for photosynthesis. Once the bird eats them, the carotenoids circulate through the their bloodstream to the feather follicles where they express as colours. And if you see for example a robin with a faded, rusty breast, it may be a sign they’re not getting enough carotenoids in their diet.
The third type of pigments are the porphyrins, made by modifying amino acids in the liver and other tissues. They can produce a range of colours - red, pink, green and brown - porphyrins are what makes plants green and our blood red. It’s rare for them to be used as colouration in mammals, but some groups of birds like owls and pigeons, use porphyrins as pigments.
And the coolest thing about them might be what we don’t see. When you expose them to UV light something amazing happens - they glow with an intense red.
Birds, unlike us, can see into the UV spectrum. So as gorgeous as they look to us, birds with porphyrin-based colouration may look even more alluring to each other.
Those are our three pigment types - melanin, carotenoids and porphyrins. But there’s one more pretty amazing way birds get their colours. It’s called structural colouration.
Pigments produce colour by absorbing all but certain wavelengths of light. Structural colouration scatters the light. As it hits a bird’s feathers it encounters a complex lattice of keratin and air vacuoles that refract and reflect it.
One form of structural colouration results in ‘constructive interference’ that reinforces the shortest wavelengths - those in the blue range. That’s how we get the brilliant colours of a blue jay or a mountain bluebird - incidentally by the same principle that makes the sky blue.
But some birds have an even more complex structure at play that reflects different wavelengths at different angles. That produces iridescence, the multi-colour metallic shine found in magpies, pigeons, grackles and others.
Structural colouration can also reinforce wavelengths in the UV spectrum. There are many species of birds in which males and females look identical to us… but they have different patches of UV-reflecting feathers, letting them easily identify amongst themselves.
Together, those four sources give us the enormous spectrum of bird plumage. And some of them do much more than just provide striking colour. This video’s been all about how birds look as impressive as they do. And next time, we’ll delve into why they look the way they do, in some pretty unexpected ways.