My favorite fact about birds is about their feather color.
Blue feathers are not blue - there is no blue pigment in them!
Instead, it's the structure of the feather that makes it look blue.
I have understood that a little bit, but not at a very detailed level.
So I reached out to another Youtube channel called Backyard Expeditions.
He does really interesting nature videography and talks about wildlife.
I asked him to explain, on a physical level, how structural color works.
And the results were amazing, so check this out!
A hummingbird in the Talamanca Mountains of Costa Rica.
From this angle, while still beautiful, it is quite plain.
But then it turns and WOW!
Just the right angle and it is spectacular.
And you can see why it is called the fiery-throated hummingbird.
This radical change in appearance is because it, and other hummingbirds, are iridescent.
At one angle they are kind of dull.
And another, they are strikingly beautiful and colorful.
This is achieved not through pigment, but by the way light interacts with microscopic
structures in the feathers.
Structural color.
The feathers of this hummingbird are comprised of different layers acting as a thin film
over the feather structure.
On a microscopic level, when light hits this film, some of it is reflected off the upper
boundary, while some is refracted by the material, changing angle as it goes through before being
reflected off the lower boundary.
The distance the light travels through the layer determines what color is reflected.
For this intense red of the fiery-throated hummingbird's throat this distance has to
be 625 to 740 nanometers wide, while for the blue cap it must travel a shorter distance
of 450 to 485 nanometers.
Having to be the exact wavelength of the light being reflected.
When the light shines through, the light that is reflected off the lower boundary goes further
and is out of phase with the light reflected off the upper boundary.
If they are a full wavelength (or to complicate things a little more, a whole wavelength multiple)
the light waves constructively interfere, creating an intense color.
At a different angle, the light does not travel the exact distance and the reflected light
now deconstructively interferes, and the iridescent color does not show up.
Explaining how this bird can go from dull to colorful with a turn of its head.
What about this Jay?
Or this Bluebird?
Or this Blue Grosbeak?
If you shine a light through any of their feathers, you see the color vanish, like on
this Macaw feather.
Because the blue is structural, just like those on the hummingbirds.
In contrast to the pigment-based banding on this pheasant feather, which remains the same
color no matter where you put the light on it.
These blue feathers are a little different than those of the hummingbird's.
They aren't iridescent, appearing blue from any angle.
On a microscopic level, the feathers of a Bluebird contain a keratin matrix of nanochannels
that form bubbles.
These bubbles are separated by a few hundred nanometers.
For the striking blue on this Bluebird they average 450 to 485 nanometers apart, which
if you remember from the film on iridescent feathers, matches the wavelength of blue light.
Just like with iridescence, constructive interference creates the vibrant color.
While blue is enhanced, other colors like red get cancelled out as the waves deconstructively
interfere.
But why does the Bluebird always look blue, while the Fiery-throated Hummingbird loses
its signature vibrant throat if it looks away?
In a Bluebird, the matrix of bubbles is quite amorphous.
It isn't quite random.
When natural light hits it, the light gets scattered in every direction, so no matter
what angle it is viewed at, you see the same blue.
However, under true directional light, the color will shift based on what angle it is
viewed at.
Because the nanostructure is not truly random.
Same with the macaw, and same with any other non-iridescent structural color on birds.
This is part of a collaboration where we each made a video for each other's channels.
So if you want to see me get really excited about woodpeckers, you can go over to Backyard
Expedition's channel, and you can check out that video.
For more videos like this in the future, you should subscribe to this channel, and also
go over to Backyard Expeditions and subscribe to him.
Thanks for stopping by this week to learn what makes Life awesome!