Woodpeckers can pound trees as many as 12,000 times a day – hunting bugs, building nests and seducing mates. They apparently do this without a splitting headache or brain damage because their head acts like an absorbent helmet, thanks in part to spongy bone material between the beak and the braincase, was the thought. But according to new research published in Current Biologythe opposite is true: a woodpecker skull is actually very stiff.
Logical too, writes the international team of scientists. If the head were to absorb a lot of energy, it would also be less efficient at carving wood, just as a rubber mallet gives less impact than a metal one. Those pieces of spongy bone are meant to prevent the skull from breaking, not to cushion shock, they suspect.
Using a high-speed camera, they filmed six woodpeckers of three different species, including the great spotted woodpecker, as they hacked into pieces of wood. They then measured how much points on the beak and around the eyes move toward each other during a blow. It turns out that the skull does not or hardly spring back.
The filming was also quite a tour, e-mails Sam Van Wassenbergh of the University of Antwerp, first author of the study. The birds may have been in an aviary, but take a look at the sharp images from the side with a sensitive high-speed camera, while you don’t know when they will pound. “All in all, a videographer’s nightmare.”
Harder works better
And that brain damage? To see which blows the brain actually receives, the scientists reproduced woodpecker heads in detail in the computer, partly on the basis of their measurements. These models first confirmed that a stiffer skull chops pieces more efficiently than a shock-absorbing one. In addition, it was calculated that woodpeckers remain well below the threshold for concussions even without special damping, partly due to the relatively limited size of their brains.
The researchers used available knowledge about the susceptibility to concussion in primates. In reality, it’s likely that woodpeckers’ brains are even better equipped for harder blows. For example, their skull contains relatively little brain fluid, so that the brain sloshes back and forth less.
Moreover, a scientific study from 2018, published in the trade journal Plos One, that woodpecker brains contain many so-called tau proteins. In the human brain this indicates damage, but it is possible that the proteins in the birds protect brain cells as a preventive measure.
A convincing study, says Lorna Gibson, who has done a lot of research on woodpecker heads as a professor of materials science at the Massachusetts Institute of Technology. The results match what you would intuitively expect, she emails: with a shock-absorbing skull, woodpeckers would simply be less good at what they do.