You may have never stopped to think about it, but how do feathers grow?
Do they grow out through the skin like hairs?
I've never seen a partial feather like this.
The truth is more bizarre than you you would expect.
Let's look how feathers are formed!
Feathers are made out of keratin, the same protein your hair is made of.
And just like your hair grows from a hair follicle, the feather grows out of a feather
follicle.
We actually have time-lapse footage of a feather follicle forming.
These are all skin cells.
They move towards each other and gather into tiny bumps in the skin.
There are chemical signals that tell the bumps how far apart to form.
The center of each bump will grow into a feather.
The edges of each bump are the feather follicle.
This area goes through massive growth.
The cells here divide and grow, divide and grow, almost as fast as they can.
The new cells they produce push out in a vertical column.
This is the feather growing.
This might help you understand what's going on.
Pretend this is the feather follicle, and this is the new feather growing in.
As new cells are added at the base of the feather, it pushes the rest of the feather
upwards.
You can just imagine how much energy is being spent at the bottom to create all these new
cells.
At the bottom of the feather all the cells are undifferentiated skin cells, but they
quickly start to differentiate and form the overall shape of the feather.
So just as my fingers are all separate, this is how the different barbs would form.
My hand is actually very similar to a downy feather.
It's a lot of different barbs and they are all connected at the bottom.
Once the feather has formed that differentiated feather shape out of skin cells, the skin
cells go through a process called cornification.
Each of the skin cells will produce a keratin skeleton inside of themselves and it makes
them very, very strong.
It's made of protein.
Once that skeleton is complete, they get rid of all their organelles and the nucleus, which
means that the cell is dead.
All that's left behind is that strong skeleton of protein.
I should mention at this point that this delicate work is all happening outside the bird, right
on the skin surface.
So to protect the process from dirt and bacteria, the whole feather is inside a protective cylinder
also made of keratin.
You can see these cylinders on birds sometimes.
They look like little white lines.
It's a new feather under construction.
These are called pin feathers because they look like pins, or blood feathers because
there is still some blood circulating inside of them as the cells finish their growth.
Inside the tube, the feather is organizing.
Here is a cross-section of what is happening.
The center is just supporting cells providing a frame for the feather cells to stay in place.
You can also see the blood vessels in here.
On the outside is the protective waxy cylinder.
The feather, in red, has several barbs, and these little lines are barbules, the smallest
parts of the feather.
Using different cellular directions the bird can form different feathers.
This is a downy feather, with long barbs that are barely connected at the end.
But the bird can also print flight feathers, semiplume feathers, or bristles.
It's all the same process, just different instructions.
As the feather is printed, color is added.
Let's talk about black, because that is a black pigment.
It's the same pigment that you might find in your own hair.
In this case, this is a silver pheasant feather.
You can see that as the feather was growing, pigment cells were added into the feather.
So everywhere you see a black line, that's somewhere that a pigment cell was added.
Everywhere that you don't see a black line, that's somewhere where it was not.
In some birds this happens at a constant rate.
Like the crow.
There were lots of pigment-producing cells jumping in the whole time its feathers were
growing, leading to even, black feathers.
Or if you look at the toucan, there are lots of pigment cells jumping in on its back feathers,
but none in its front feathers.
Where it gets really wild is where there are patterns on a single feather.
Take this feather, this is a silver pheasant feather.
Most of the feather is white, so no pigment cells were put there.
But then there are thin black lines.
So the pigment producing area was very thin and it moved around the follicle.
What about this one?
This is a Great Argus Pheasant Feather.
As the feather was growing, there were small amounts of pigment being put all over the
feather, small amounts of melanin, but then certain groups of cells would jump in and
produce a black spot.
Isn't it amazing that cells can coordinate together to make a big pattern like this,
even though they are so small?
One more feather.
This is a Kookaburra tail feather, and you can see that as the feather was growing, cells
were turning on and off, leading to these large stripes.
Then to make the white tip at the end, cells were turned off, except for when the times
when it was making a band.
We are still learning exactly how this process works, so there will be new discoveries about
how feathers form.
And that's just melanin.
There are many other pigments that could be included.
It turns out that red, yellow, orange, black, and brown are all pigments in the feather.
But blue, green, and white are really different.
Here is one video you can watch on the subject, and we will have a guest video in a few weeks
that teaches some advanced lessons on these types of color.
This process is amazing and complex, but it's happening all the time.
Bird feathers are replacing themselves regularly.
Old ones fall out, new ones grow in.
It's why birds are able to have a covering which is so light and delicate.
If you would like to grow your knowledge about birds, subscribe!
And take a microscopic look at these other videos to learn more.
Thanks for stopping by this week to learn what makes Life awesome!