If humans were covered in feathers, could we flap our arms and fly?
What if I told you that it would take up to fifty pounds of chest muscles just to flap
your arms hard enough to lift yourself off the ground?
Let's look at bird muscles and see just how much strength it takes to fly!
Birds are missing a lot of body parts that we have, like teeth, a big brain, and a big
stomach, because flight is difficult.
Every ounce they add to their body is an ounce they have to lift into the air.
But one thing that birds have LOTS of is muscle mass.
The average bird only has 175 muscles, compared to a human's 600 muscles.
But the two biggest muscles, the pectoralis majors and the supracoracoideus muscles, the
chest muscles, are a significant fraction of the entire bird's weight.
In Mallard ducks these muscles are about 7% of body mass.
So a 150 pound human would have pectoral muscles that weigh ten and a half pounds.
In Mourning doves it's 16% of body mass, or 24 pound pectorals.
And hummingbirds have chest muscles that are 30% of their total body mass, or 50 pounds
on a human.
These muscles are so amazingly huge and strong that the bird needs reinforced rigid bones
to avoid breaking its own wings while flapping.
These muscles are so big that birds have a support structure just to let them connect
to the bird.
It's called a keel, and it's like taking this bone and extending it outwards in a fan shape.
The bone needs all this extra surface just so the huge pectoral muscles can attach.
And speaking of incredible adaptations, bird have one other trick built into their pectoral
muscles.
I'll show you with my own arms.
Birds need to push a lot of air down and back in order to fly.
And to apply all that force they have huge pectoralis major muscles Once their wing is
down, though, they need to lift their wing back up.
In humans, we have a small muscle to do that.
It's called a deltoid, it's right here.
Birds have a fairly large muscle called the supracoracoideus muscle to do the same thing.
But it's also located here on the front.
Behind the pectoralis major muscle but in front of their organs and stuff.
So if muscles only pull, how does the supracoracoideus muscle lift the wing?
It's got a pulley, a tendon that reaches up over the shoulder and connects to the wing
bones in the back, which lets them pull that wing up again.
One more thing about bird muscles?
Birds have tiny muscles on each feather.
Each feather follicle has tiny muscles that connect to other feather follicles.
By pulling with these muscles, the bird can adjust groups or even individual feathers.
This gives the bird very fine control over their shape, which controls how they fly.
This complex control is used for social expression and displays, but its primary use is to keep
the bird up in the air.
I think we can see that birds have put a lot of effort into their muscles.
The large pectoral muscles that make up a huge fraction of every bird's weight.
The complex pulley that reaches over their shoulder and lets them lift their own wing
muscles.
Or the complex network of tiny muscles that let them control their own feathers.
And at this point, I think we know the answer to the original question.
Because flight is not just about having feathers.
Humans are not strong enough to fly, even with feathers.
They're not strong enough to lift themselves up into the air using just their pectoral
muscles.
Because flight is all about replacing your organs and your teeth and your big brain and
replacing it all with muscle mass, just so you can lift yourself into the sky.
It's one of the many compromises that enable flight.
Thanks for bulking up your knowledge about birds.
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