WHY DON'T WOODPECKERS GET CONCUSSIONS LIKE WE DO???

Wood is tough stuff, which is why we use it hold up houses and trees use it to hold up themselves. 

If you've ever swung an axe against a tree, you know that chipping away wood takes a lot of force. 

NOW IMAGINE CHIPPING AWAY THAT WOOD WITH YOUR FACE

That's what it's like to be a woodpecker. Hammering away a tree, 20 times a second, 10,000 times a day. The force of a peck is like headbutting a tree at full sprint, which you should not try at home.... 

So why don't woodpeckers get concussions?

They say it's not the fall which kills you, it's the sudden stop at the end. Anyone who has watched a crash test video knows that when the car stops moving, the bodies inside it don't. This is basically the inside of your head right before you get a concussion. 

The human skull is surprisingly strong and flexible, but the delicate brain in the middle is reminiscent of jello floating in liquid. A rapid deceleration can cause your brain to hit the inside of your skull and damage your neurons and other cells, this is called a concussion.  If nerves are damaged in the right area then you can lose consciousness but you don't have to be knocked out to get a concussion. Even smaller impacts can cause lasting damage. Chronic traumatic encephalopathy (CTE)  is a brain disease caused by repeated impacts which can lead to complicated symptoms. When doctors did autopsies on former professional football players (NFL) they saw brains which looked wasted away from years of repeated impacts that weren't "technically" concussions. 

It's a big problem. Some scientists are wondering if we can learn anything from the humble woodpecker. 

Woodpeckers are built for headbanging. Spongy skull bones, even special eye lids which close just before impact, but their real anti headache secretes are deeper inside. Woodpeckers will often hammer trees to look for food. Once they have found this food they will use their long tongue like a spear to catch the unsuspecting insects. The woodpeckers tongue is typically around 3 times the length of their beak, so where do they keep it when it is not being used? As it turns out, there is a bony support inside the woodpeckers skull called the Hyoid. We have a Hyoid too, but ours just sits underneath our tongue, but in a woodpecker it goes out the back of its mouth all the way around its skull and between its eyes. Scientists believe that this bone and muscle wrapper may act as a seat belt and absorb some of the shock when a birds head decelerates. 

One of the basic equations in physics is that force is equal to mass times acceleration or deceleration (F=ma). What really matters for impact injuries is how much area that force is being applied to, or why you should lie on a bed of nails and not do a headstand on one. From the side the human brain is basically a semi-circle orientated in such a way that impact from the forward/backward axis focuses the force on a small area. In contrast, a woodpeckers brain is oriented differently, so forward/backward forces are distributed evenly over a larger area. In addition, the woodpeckers brain is packed more tightly in their skulls and so they do not slosh around like the human brain does.

g-force is our measure of relative acceleration. We typically feel 1 g, the standard acceleration of gravity on earth. The g-force a body can survive depends a lot on how long that body is being exposed to the g-force. If you love roller coasters, you have probably experienced several seconds of 5 g's and walked away smiling. Race car drivers have survived crashes with over 200 g's but only because that deceleration was limited to a few milliseconds.  It takes less than 1 millisecond for a woodpeckers head to move from full speed to stopped. In that  amount of time, our brains could take 300 g's before concussion. However, woodpecker brains can withstand more than 4000 g's before concussion.  

So this brings us to our final and most important reason why woodpeckers don't get concussions

J.B.S Haldane wrote in a 1926 essay on being the right size that you can drop a mouse down a thousand yard mine shaft and it will be shocked but walk away. Drop a human down the same mine shaft and its bones will be broken. Drop a horse down the mine shaft and it will splash. 

As an animal, or an animals brain, gets smaller the volume and mass will drop by the cube but the surface area goes down by the square. So a woodpecker brain might have much much less skull area to absorb impact than we do but it is significantly lighter. 

So the main reason why woodpeckers don't get concussion is because they are small!