They bang their beaks on the wood, which can be heard from afar. The brain of the woodpecker is said to be protected from excessive vibrations by a kind of shock absorber effect. However, this common assumption has now been refuted by a study: According to the analyzes the shocks are not cushioned – the birds’ heads hit like a stiff hammer. Dampening would also be counterproductive, because then the hits would be less powerful. Nevertheless, the woodpecker’s brain does not seem to be threatened with damage: due to its comparatively small size, it is not critically shaken, the researchers explain.
A comparatively light blow is often enough to give us a headache. However, if the brain is shaken even more severely, it is known that life-threatening damage to the sensitive nerve tissue can occur. But the woodpecker seems to get along well with it: the famous birds constantly ram their beaks into the hard wood to get food or to build nesting holes. People have been wondering for a long time how they manage to do this without harm. The common explanation for this was that the blows in the birds’ heads were cushioned – as if a crash helmet were protecting them. From a scientific point of view, however, this was only an assumption. Certain anatomical features have been associated with a shock absorber function. But the alleged shock-absorbing effect of the punch itself has not been properly documented.
Alleged attenuation on the trail
The researchers led by Sam Van Wassenbergh from the University of Antwerp have now closed this gap. First, they accurately captured the dynamics of the head as it flapped in three woodpecker species using high-speed imaging. Using anatomical clues on the skull, they were able to see the extent to which there were shock-absorbing effects. But the analyzes now showed that they don’t exist at all. There were hardly any delays in movement of the skull structures, as would be expected with a shock absorber effect. Instead, the woodpecker’s head hits the wood stiffly like a hammer, the scientists conclude.
The team also ran biomechanical model simulations of the birds’ flapping behavior. They made it clear that a shock-absorbing effect would even be nonsensical. Because it would impair exactly what is required: impact force. If there were a shock absorber system, the woodpeckers would have to hammer much harder to achieve their typical impact strength. The scientists explain that the protective effect would then be nullified again.
Apparently no cushioning needed
But how do birds escape a concussion? As the further investigations of the scientists showed, a protective function is apparently not necessary at all. A force comparable to that of a woodpecker would actually cause damage to the human brain, but the relatively small birds have different physical effects than ours: the lower mass means less strain on the brain. The researchers’ calculations show that the vibrations in the woodpecker remain well below the level that causes damage to us.
“The lack of shock absorption does not mean that the woodpecker brains are in danger in the seemingly violent impacts,” concludes Van Wassenbergh. “Even the strongest shocks from the more than 100 analyzed blows should not be dangerous for the woodpeckers’ brains, since our calculations showed that the brain is less stressed than in people who suffer a concussion.” From an evolutionary point of view, the results can also explain why there are no woodpeckers with much larger heads and neck muscles. Such animals could hit even harder, but then there would actually be a risk of concussion, the researchers say.
The results thus refute the long-held story of shock absorption in woodpeckers, which has been widely shared in science and in the public sphere. “While filming woodpeckers in zoos, I’ve seen parents explain to their children that woodpeckers don’t get headaches because they have a shock absorber in their heads,” says Van Wassenbergh. As has now been shown, this initially plausible explanation is not correct.
Source: Cell Press, Article: Current Biology, doi: 10.1016/j.cub.2022.05.052
Video: Slow-motion clips of high-speed video of head impact in three woodpecker species.
© Current Biology/Van Wassenbergh et al.