I'm going to show you a secret.
Birds, animals, and people all have microscopic tricks that make them look different than
they are.
My name is Steve Bush, and I'm going to introduce you to a secret world that's hidden all around
us.
Prepare to learn about the secrets of color created by shape.
Birds have different pigments in their feathers.
Red, yellow, orange, black, and brown are all pigments.
But there's colors which use more... unusual methods to appear.
Blue This feather looks blue, but there are no
blue pigments in it.
There's no blue chemical.
So if you look through the feather at a light, the blue disappears.
Instead of a blue pigment, these feathers have small air bubbles that are just the right
shape on the nanometer scale to reflect only blue light.
We'll talk about how that works in a second.
But just take that in.
When you look at the bright blue feathers of a blue and gold macaw, the bird's feathers
are actually pigmented dark grey, the color you see when you hold it up to a light, and
there's a layer of bubbles that makes the bird look blue.
This is not just true in parrots.
There is no blue pigment in any bird in the world.
Bluebirds, blue jays, peacocks, parrots.
Every single blue feather you've ever seen has some trick based on the shape of the feather
that makes it look blue.
Now let's talk about how that works.
As the feather forms, there are tiny, tiny drops of water mixed in with the protein of
the feather.
The water evaporates and leaves air bubbles behind.
It's similar to this sheet of bubble wrap.
Imagine this is the surface of a blue feather.
There's air bubbles, and there's spaces between them.
The bubbles are a mix of different sizes, mostly spherical, and most importantly, are
just under 500 nanometers apart, on average.
The average distance is the key, because that is the exact color of light which will be reflected.
Larger air bubbles reflect darker shades of blue, because the average distance between
them is shorter, which equals a darker blue.
Smaller air bubbles reflect lighter shades of blue because the average distance is longer,
or lighter blue.
If that makes no sense, let's do a quick demonstration.
Why does a field of air bubbles reflect the wavelengths that equal the average distance
between them?
We'll have to cover that some other day, because honestly I don't understand.
It's the way the universe works.
If you understand physics, please get in touch because I'd love to learn.
You'll notice that the feather has dark grey pigment in it.
This grey pigment absorbs every kind of light that hits it.
But we know the blue has already bounced off the air bubbles, so the grey pigment is absorbing
every color EXCEPT blue, because the blue already turned around and left.
This makes the blue way more vibrant.
Here's a structural blue feather without dark grey pigment.
Kinda meh.
Oh yeah, there's one more thing to say about blue.
There's several more ways that shape can make stuff look blue, but only one other is used
by birds as far as I know.
That's to use thin, transparent films of just the right thickness.
I don't want to overwhelm you by explaining two things in a row, but you can tell the
difference by looking at them.
Feathers that use air bubbles look blue from any angle.
Feathers that use transparent films will be bright, even metallic blue, from one angle,
but look black from other angles.
Green Now that you understand blue, or at least
you understand that blue is a trick, green is EASY.
99 percent of green feathers are just a structurally colored blue feather with some yellow pigment
on top.
Just like you learned in primary school, blue plus yellow equals green.
DONE.
You're a world-class expert on green feathers now!
But what if part of this green system breaks down?
What if the structural blue is missing or the yellow pigment?
This happens sometimes.
Budgerigars are naturally green, but babies are sometimes born that are blue or yellow.
Now that we know how green is formed, we know what happened.
Blue birds are missing their yellow pigment, and yellow birds are missing their air bubbles.
It's that simple!
100 percent of blue feathers are structurally colored, but there's an exception in green feathers.
The Turacos, which are fruit eating birds native to Africa, actually produce a green
pigment in their feathers that is based on copper.
That's the only exception though.
Every other green feather is a structural color.
WHY Why do birds go to so much trouble to produce
nano-scale shapes in their feathers?
Why don't they just make blue or green pigment?
Is it for camouflage?
Truthfully, we don't know.
Our best guess is that blue pigments in birds, mammals, and reptiles just never developed.
There's zero blue pigments in any bird, mammal, or reptile as far as we know.
But blue and green are great camouflage in trees, so animals that have those colors are
more successful at hiding.
More ability to hide from predators equals more offspring equals more green feathers.
White Oddly enough, white is also a structural color.
There's channels and cracks in the protein of the feather that reflect all light, making
it look white.
The way to understand this is to think of how clear water freezes into white snow.
The chemistry of the water doesn't change, but the shape does, and that makes it reflect
differently.
So next time you're out and see a blue jay or bluebird, you can look the bird in the
eye and say, "I know your secret."
You know that their feathers are colored by shape, not by pigment.
And then you can turn to the person next to you and introduce them to this crazy hidden
world that's in plain sight all around us.
I hope you enjoy that experience.
Go spread the word.
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