Why Woodpeckers don't get Brain Damage
We often talk, metaphorically, about banging our heads against the wall. Luckily, for most of us, talking about it is as far as it goes. But for some animals, really banging your head against something hard, many times a day, is a fact of life. So why don’t woodpeckers - that are masters at this and do it to attract mates and also open up holes in trees to find insects to eat - get headaches and brain damage? The popular theory, for decades, was that these birds have spongy tissue at the base of the beak that soaks up the shockwave of the beak striking the tree, and this avoids transmitting the force to the brain. Surprisingly, it was such an attractive theory that everyone embraced it but no one actually thought to test it. And, speaking with Chris Smith, that’s where Sam Van Wassenbergh comes in…
Sam - Scientists have hypothesised that woodpeckers have a built-in shock absorber in their head to prevent themselves from getting headaches or injuries in their brain. But this hypothesis has never been tested so far, so that's what we wanted to do.
Chris - What sorts of forces, when a woodpecker is striking a tree, will its tissues, including its brain, encounter then?
Sam - When the beak impacts the tree, you have a strong shock. So the brain will suddenly come to a stop and the tissues will be pushed against each other. Where at the back of the head, they will also be pulled away from the brain case. If the shock is too high, you will get a concussion.
Chris - We see this in human athletes, don't we, and people in the sports field when, they have a sudden deceleration injury of their head. So it seems logical to assume that an animal that is repeatedly banging its head against a tree probably is gonna encounter some of the same problems.
Sam - Absolutely. Yes. If you watch woodpeckers smashing their head against trees, it's a very logical idea to think that they have a benefit from having something that cushions this blow. It's definitely a problem for football players or boxers or any kind of people that experience these strong shocks to their head.
Chris - So how did you address this then?
Sam - Well, we went out to zoos where they have woodpeckers and there are not too many in Europe. We took our high speed cameras so we could film up to 4,000 frames per second. And then we played these videos back frame by frame and tracked different points on the head of the woodpeckers, like we would do with crash test dummies. So comparing these different parts on the head and how they experience the shock.
Chris - How did you get them to hammer on demand? Because other people who've studied woodpeckers, because there was a paper a few years ago, where researchers used an old fashioned typewriter and tapped out a few words and the wood pickers would respond by tapping themselves. Did you just wait for them to tap or did you stimulate the tapping in some way?
Sam - No, we just waited for them to tap and this was not such a big problem. These birds really like to hit their head against the wood.
Chris - So you get these pictures, you analyze frame by frame. What are you comparing with what? So you're just seeing the beak hit the tree and then what do you measure?
Sam - So if there would be any cushioning going on between the beak and the brain case, we would see a difference in the movement profiles of the beak and the brain case. So we compared the deceleration values we got out of our data set. And well the result was that there was no difference between the beak and the brain case. So there was no evidence that there's any shock absorption going on. So it's clear that these woodpeckers are not going for this option to absorb the shock.
Chris - You're saying if they did have some kind of spongy tissue that was there to soak up, like a shock absorber, some of that impact so it wasn't transmitted to the brain, which is what other people have speculated. That you would see the beak changing its position relative to these other structures in your pictures. And you just don't see that. So you're ruling that out.
Sam - Yeah, exactly. There's hardly any movement between the beak and the brain case.
Chris - What do we infer is happening to the brain then under those circumstances?
Sam - Well, the brain certainly experiences shock at this moment, but we calculated that it is not strong enough for birds to get a concussion. Birds are just a lot smaller than humans and they just can withstand higher shocks. It's a law in biomechanics that smaller animals can withstand higher shocks. The birds still have some safety margin before they would get any damage to their brain.
Chris - Has anyone gone inside the head of animals like woodpeckers after they've been pecking to see if there are evidences of brain changes and whether this is just an unfortunate cost of this behavioural aspect? Has anyone done that?
Sam - There has been one study, they found some proteins that are involved in damage repair. They call these the Tau proteins and we also see them in humans after they get concussions and things like that. So there is some evidence that there's damage going on. It Is an issue for these woodpeckers to try to minimize their damage.