What is one thing that being a high profile athlete and me walking into a door head first (true story!) have in common?

The likelihood of a concussion is high from the aforementioned activity.

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This is probably not the way you expected this post to begin..." I thought it was going to be about woodpeckers!" It is young padawan, it is. "Why am I reading a post about woodpeckers?" Well I would imagine for the same reason I am writing one, the question posted in the title is interesting.

So I brought up concussions for a reason, we all know that our brains are sensitive, mushy, and do not tolerate a physical beating well. When we do subject them to a beating, well... we end up concussed. However there are some animals out there whose whole lives revolve around repeated force being exerted by their heads! For example... the woodpecker:

Image Source

The woodpecker is a fascinating bird, it pecks against trees upwards of 1200 times per day to search for insects to eat, and attract mates. Trees are not comprised of a soft pillow like material (duh!) so the wood pecker has to exert some force to dig its beak into one. Quite a lot of force actually... up to 1500 x g. [1] By contrast, the force on you from a car crash with a vehicle traveling 70 mph (into a stationary object), usually generates somewhere around 100 x g.[2] So that wood pecker is really exerting some force... WITH ITS HEAD! There is a great gif that puts this force into perspective for you:

SLAM!

How in heck does that bird still have a functioning brain after spending day after day exerting that crazy amount of force on its head?!

For the answer to this we turn to an old article from way way back in yesteryear... or you know... 2011. The article was published in the journal PLoS One, and was titled "Why Do Woodpeckers Resist Head Impact Injury: A Biomechanical Investigation."

In this article (one which I am sure many of you will think is a prime example of "why the heck are we funding this shit?") researchers sought to understand what is it about the woodpeckers head that allowed it to withstand such crazy amounts of force. They justify the research with the logic that we could use the information to better design protections for our own heads if we knew of efficient ways to disperse the forces. Mechanisms which nature already seems to have down in the heads of these birds.

This particular article wasn't even the first to study this phenomenon, in fact there were many! [4], [5], [6]. In these and other works authors researched and identified mechanisms by which they thought the woodpecker could withstand the force. These ideas were about things like the shape of the birds beak, and small amount of cerebrospinal fluid, in tandem with a small brain (the smaller amount of fluid allows the brain to make more contact with the skull, leading to it moving around less and suffering less damage) helped the bird tolerate the forces. Additionally, it was published that the woodpecker likely pecks in a straight line motion which helps protect against concussions, as it is thought that rotational forces rather than ones in a straight line cause concussions [7].

Despite the work previously done and ideas drawn, the authors of the article we discuss today felt that some things were left out, for instance, whether the 3-Dimensional movements of the birds heads helped off set the forces, and whether the composition of the bone of the beak played a role in helping to allow the bird to avoid injury.

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So What Did They Do?

The authors utilized high speed cameras to monitor the 3-dimensional movements of the heads of great spotted woodpeckers during the pecking process, while the force was measured using a separate sensor where the sensor was set as the peckable object for the bird which was in a cage. In addition to this they tried to better understand the composition of the beaks and some other bones in the woodpeckers heads through use of micro-computed tomography and scanning electron microscopy (both allow for good resolution of small things, like composition of these bones!).

First... Pecking Motion

One would assume that the bird pecks in a straight line right?

What we are looking at here is the motion that the birds head makes from the perspective of several planes, you can orient your self using the box in (a) and think about what this head motion would look like. What you should take away from this is that when the woodpecker is pecking at something soft (Foam, in the diagram above) it does move in a straight line. However when it pecks against something hard (the sensor, or its cage) the pecking movement is curved.

Uh oh, but....but... people said the woodpecker uses a straight line pecking motion to avoid brain injury... well so much for that hypothesis (shakes fist angrily at the sky and gods of science for striking down that hypothesis).

What About The Structure of Their Bones?

Here we are looking at the structure of the cranial bone of two different birds: the great spotted woodpecker (a) and the Eurasian hoopoe (b)...

Heres the hoopoe in case you are curious

The Eurasian hoopoe was selected for comparison because it doesn't peck at hard objects like trees, but rather insects in the soil, so its bone structure wouldn't need to defend against the crazy g forces that the woodpecker's bones do. Which is what these images show, the cranial bone of the woodpecker is tightly packed, dense, thick, tough... wow! While the hoopoe's cranial bone was spongy like a baby's bottom. The dense cranial bone of the woodpecker is actually in plate like structures with spongy bone in between, while the hoopoe's cranial bone is just all sorts of spongy.

What Do The Forces Look Like In The Woodpecker's Beak During A Peck?

Woodpeckers beaks are shaped such that the lower beak is a bit longer than the upper part of the beak, as it turns out this is for a good reason:

You can see that the forces that are placed on the bird from the peck are primarily on the bottom part of the beak. In addition to this, there is another bone that is attached to the bottom part of the beak which wraps around the back of their skulls called the hyoid bone:

Interestingly this bone also disperses a bunch of the force from the peck. So the longer bottom part of the beak takes the brunt of the force, then the hyoid bone helps distribute the force around the skull, sort of like a seat belt does for you, distributing force across your body during a car crash.

So What Did We Learn?

• Woodpeckers peck hard! 1500 x g
• Woodpeckers don't avoid concussive forces by pecking in a straight line as was once thought.
• Woodpeckers do put the brunt of the force on the bottom of their beaks
• Woodpeckers hoyid bone distributes more of of the forces across their entire skull like a birdy head seat belt.
• The organization of dense uneven spongy bone in the woodpeckers skull helps absorb the shocks.
• These adaptations working together are what allow the woodpecker to not knock itself into a concussion as it pecks.

I had a lot more fun writing about this then I thought I would at first! I don't know if you enjoyed reading about it (I hope you did) but this was pretty interesting for me!

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Sources

1. http://www.audubon.org/news/how-woodpecker-bangs-without-brain-damage
2. https://www.wired.com/2011/04/crashing-into-wall/
3. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0026490
4. https://www.ncbi.nlm.nih.gov/pubmed/58330
5. http://www.tandfonline.com/doi/abs/10.1080/00306525.1999.9639746
6. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2006.00166.x/abstract
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4090913/
8. https://www.microphotonics.com/how-does-a-microct-scanner-work/
9. https://en.wikipedia.org/wiki/Scanning_electron_microscope

All Non Cited Images Are From Pixabay.com And Are Available Under Creative Commons Licenses

Any Gifs Are From Giphy.com and Are Also Available for Use Under Creative Commons Licences

Images from figures in PLoS One articles are available for reuse under a Creative Commons license.

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