Sheetal Potdar

While running downhill at full speed, I suddenly felt dizzy – not from exhaustion or lack of oxygen, but from being off balance. I realized it was my head bobbing up and down that was throwing me off. Once I found my bearings, it struck me how difficult it is for the human body to adjust to disturbances in sensory perception due to high-speed motion.

Formula 1 drivers while driving at breakneck speeds are impacted by extreme forces, up to 5-6 times their body weight, especially during braking and cornering. They end up developing massive necks, often nearly as large as their heads, as a result. However, not all of us are racing car drivers who train to strengthen head and neck muscles. For most of us, high-speed motion can cause feelings of nausea, dizziness, discomfort and disorientation.

This problem made me think of woodpeckers, birds that perform high-speed, high-impact movements every day without any apparent harm.

Woodpeckers experience forces of up to 1,200 g with each strike. In contrast, a human can suffer a concussion from head impacts involving 80 to 100 g. In that light, the word “pecking” feels like a misnomer – it hardly captures the sheer intensity of the impact imparted on a piece of wood.

Woodpecker heads: Shock absorbers or sledgehammers?

If you have ever watched a woodpecker in action, you would have noticed how fast their pecking motion is. It appears spectacular even in slow motion, where the intense amount of force they apply on a piece of wood is captured vividly. Their entire head seems to participate in the activity. How can woodpeckers perform such intense, high-speed motion for hours together? 

One idea that has made its way into popular imagination is that woodpeckers have a shock absorption mechanism to protect their heads during pecking. Woodpeckers have a spongy bone in between their beaks and braincases, which for many decades has been believed to perform the function of shock absorption. In fact, the anatomy and morphology of the woodpecker head has inspired the design of safety helmets and shock-absorbing protective gear. 

Yet, the idea that this spongy bone is part of an in-built biological shock absorption system to prevent damage to their brain has limited evidence. In fact, even the idea of a shock absorption mechanism according to some scientists is counter-intuitive. They argue that having a shock absorber would reduce the very force the woodpecker is imparting on the wood, subsequently prompting the bird to strike harder, which could in turn cause even more harm to its head. Biologists argue that evolving such a mechanism could be counter-productive.

In a recent study, biologists took high-resolution videos of three species of woodpeckers to test this hypothesis. They found that the way the woodpecker head decelerates after impact suggests a lack of evidence for any shock absorption mechanism. To understand this better, imagine a fast-moving object, such as the beak of a woodpecker, striking a stationary object, such as a tree trunk. At the moment of impact, the fast-moving object decelerates, i.e., it loses speed instantly. If a shock absorption mechanism were present, the head – being farther from the point of impact – would decelerate more slowly than the tip of the beak, which directly strikes the tree trunk. 

Think of a fast-moving car hitting a barricade: because it is equipped with airbags (shock absorbers), the passengers inside the car decelerate more slowly than the hood, thereby feeling less impact. Similarly, if a shock absorption system existed between the beak and the braincase (or skull) of a woodpecker, then the tip of the beak and the braincase would decelerate at different rates during impact.

In this study, the presence of a shock absorber was tested by measuring the deceleration at two points on the woodpecker’s head – the tip of the beak, and the eyes, which served as a good proxy for the position of the braincase. The researchers found that these two points faced similar rates of deceleration upon impact, suggesting that woodpeckers do not have an in-built shock absorption mechanism. If anything, the entire head of the woodpecker functions as a single, rigid unit.

The researchers also built a biomechanical model to mimic the pecking motion of a woodpecker. When they included a shock absorber in the model, it failed to achieve the force that a woodpecker applies to a piece of wood. This suggests that having a shock absorber robs the woodpecker of the force it generates through the pecking motion. Together, the scientists concluded that woodpecker heads behave more like hammers, and a shock absorption mechanism is unlikely to be involved in protection.

How are woodpeckers avoiding concussions?

Instead, their anatomy provides built-in protection against impact.

The spongy bone in between the beak and the braincase, according to this study, appears to resist force rather than absorb it. In other words, if it were absorbing the force, then it would have deformed, or changed its shape just like a sponge. Instead, it remains as stiff as possible, allowing the woodpecker head to strike as a hammer, thereby resisting the force.

Other adaptations such as a smaller brain, which is tightly packed in the braincase with very little space between the two, also helps woodpeckers withstand the deceleration. Further, there is only a small amount of cerebrospinal fluid – the protective fluid that normally fills the cavity between the skull and brain in most animals. This reduces sloshing and contributes to the rigidity of the head. Furthermore, proteins involved in damage repair are found in higher abundance in the frontal lobes of woodpecker brains, suggesting faster access to repair mechanisms.

Behavioral adaptations, such as selecting the right tree trunk and striking at maximal speeds, also provide a form of preemptive protection. These adaptations allow the woodpecker to transform its head into a hammer, removing any need for an external helmet.

What about us?

Humans, on the other hand, are far less equipped to handle head trauma. Even with protective equipment like padded headgear for boxers and HANS (Head and Neck Support) devices for F1 drivers, concussions remain a significant risk. Our brains are large, surrounded by fluid, and evolutionarily unprepared for repeated acceleration and deceleration. Even seemingly innocuous activities like running downhill, can cause significant discomfort and disorientation.

Woodpeckers, by contrast, are perfectly adapted for their task – executing high-impact pecking for hours at a stretch without any discomfort.