54 PHYSICS TODAY | JANUARY 2024
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Sam Van Wassenbergh is a professor
of animal mechanics and Maja Mielke
is a doctoral candidate in the functional
morphology laboratory at the
University of Antwerp in Belgium.
W
hen knocking away pieces of hard woody bark to
fi nd food, digging nesting holes into tree stems, or
making drumming sounds to lure mates or an-
nounce their territories, woodpeckers generally
strike trees with their beaks at speeds of 20 kilo-
meters per hour and can reach rates up to 30 times
per second during drumming. So a sudden deceleration would
exceed the threshold that would render a concussive blow— at
least to a human brain. But to judge from many popular ac-
counts, internet blogs, information panels in zoos, and educa-
tional television programs, the birds’ brains emerge unharmed
thanks to shock- absorption structures in the skull.
Bird enthusiasts may be comforted by the idea that a shock
wave traveling backward from the impacting beak becomes
cushioned before it reaches the brain. And the idea gained
strength in the past decade when computed tomography re-
constructions revealed a zone of spongy bone at the front of a
woodpecker’s brain, as shown in fi gure 1.
That porous zone consists of interconnected bony rods
and plates, which could theoretically be compressed on impact
to reduce the shock to the brain. But although it inspired the
design of new shock- absorbing materials and helmets, the
hypothesis had not been tested. What’s more, several scien-
tists strongly doubted it even earlier. In the 1970s psychiatrist
Philip May and coworkers saw the potential of learning from
anatomical adaptations in woodpeckers to withstand re-
peated blows. Yet in their 1976 Lancet article, they questioned
whether the cranial absorption of shocks was part of those
adaptations. “If the beak absorbed much of its own impact,
the unfortunate bird would have to pound even harder,” the
authors wrote.
It would be maladaptive for a bird to fi rst
build up suffi cient kinetic energy to deliver a
strong hit to a tree by accelerating its head for-
ward, only to lose part of that energy into its
own built- in skull– beak shock absorber. (With
ophthalmologist Ivan Schwab, May was post-
humously awarded the 2006 Ig Nobel Prize in
Ornithology for his work.)
Video evidence
As part of an international research team two
years ago, we looked at three species of wood-
peckers to see whether shock absorption was
really taking place between the beak and the
brain. We recorded high- speed videos of the
birds during pecking. In Europe, those videos
were made in four zoo aviaries with a black
woodpecker (Dryocopus martius) and great spot-
ted woodpecker (Dendrocopos major). In Canada,
recordings were made of two pileated wood-
peckers (Dryocopus pileatus) kept in the labora-
tory. Akin to how video is used in automobile
crash tests, we used consecutive video frames to
track the movement of landmarks on the birds’
heads and then calculated their peak decelera-
tion with impact.
The landmarks for all of them were two
spots on the beak and one on the eye, which we
Why woodpeckers don’t get concussions
Sam Van Wassenbergh and Maja Mielke
Contrary to popular belief, the birds don’t have shock absorbers in their heads.
FIGURE 1. A BLACK WOODPECKER and an x- ray computed tomography
reconstruction of the left half of the skull. The enlarged circle shows the
spongy bone, located at the interface between the beak and the cranium,
that had been hypothesized to serve as a shock absorber.
23 February 2025 10:51:33
JANUARY 2024 | PHYSICS TODAY 55
assumed moves along with the front of the braincase. The pi-
leated woodpecker had an additional landmark, a small white
dot painted on the skin covering the braincase, as shown in
fi gure 2a. We then compared the average deceleration profi les
between the landmarks on the beak and the braincase for more
than 100 pecks.
We consistently found no reduced deceleration of the brain-
case compared with that of the beak, as seen in the results in
fi gure 2b. Hence, between those sites no cushioning occurs by
means of spongy bone compression or any other method. The
woodpecker’s head functions as a stiff hammer—not as a shock
absorber. Furthermore, our biomechanical- model calculations
prove that potential shock absorption within the skull would
have reduced the penetration depth in wood by the beak for a
given head- impact speed. Although such a built- in damper
would slightly reduce the brain’s acceleration, it would never-
theless be a waste of energy: The same work done on the wood
with equally reduced brain accelerations can be achieved if the
bird hits the tree more gently. Consequently, those data
prompted us to conclude that the observed minimization of
cranial shock absorption is a logical, adaptive outcome in birds
that have evolved a wood- pecking lifestyle.
Avoiding injury
But without shock absorption in the skull, how do woodpeck-
ers protect their brains from injury? Our data show that wood-
pecker brains are subjected to decelerations of up to 400 g,
where g is the acceleration due to gravity. That far exceeds the
estimated threshold of 135 g to cause concussions in humans.
As pointed out in 2006 by MIT’s Lorna Gibson, the answer lies
in the mass difference between the brains of woodpeckers and
those of humans. She found that the keys to the birds’ ability
to withstand high decelerations include their small size, which
reduces stress on the brain for a given deceleration; the short
duration of the impact, which increases their toleration of it;
and the orientation of the brain in the skull. The pressure in
the woodpecker’s brain under its own deceleration is propor-
tional to the product of the bird’s deceleration, the mass den-
sity of its brain tissue, and the brain length, or volume/area.
The relevant length is that of the brain in the direction of
impact. The brain of a woodpecker has roughly one seventh
the length of a human’s. And thus the woodpecker’s decelera-
tion threshold for concussions equivalent to the human’s
threshold would be 7 × 135 g, or about 1000 g. The upshot is
that even the hardest hits from our data set— roughly 400 g—
are not as violent as they appear. The birds maintain a consid-
erable margin of safety and still suff er no brain injury, even if
they were to accidentally hit a material stiff er than wood; for a
comparison between human- and woodpecker- brain pressures
in response to the strongest decelerations, see fi gure 2c. On the
other hand, the relationship between brain pressure and length
can explain why no giant woodpeckers exist that can drill holes
much deeper than those drilled by currently living species.
Shock absorption in woodpeckers is a good example of how
hypotheses can spread to become common beliefs even with
no scientifi c evidence supporting them. The combination of
spectacular behavior receiving plenty of popular- media cover-
age and humans focusing on brain- protection adaptations
when it comes to head impacts can be misguiding. The two
factors may be responsible for the mythologizing of how
woodpeckers avoid injury. We hope that our biomechanical
evidence can help change that belief.
We would like to thank our collaborators Erica Ortlieb, Christine Böh-
mer, Robert Shadwick, and Anick Abourachid.
Additional resources
‣ S. Van Wassenbergh et al., “Woodpeckers minimize cranial
absorption of shocks,” Curr. Biol. 32, 3189 (2022).
‣ A. A. Biewener, “Physiology: Woodpecker skulls are not shock
absorbers,” Curr. Biol. 32, R767 (2022).
‣ L. J. Gibson, “Woodpecker pecking: How woodpeckers avoid
brain injury,” J. Zool. 270, 462 (2006).
‣ E. R. Schuppe et al., “Evolutionary and biomechanical basis of
drumming behavior in woodpeckers,” Front. Ecol. Evol. 9, 649146
(2021).
PT
INTRACRANIAL
PRESSURE
(kPa)
100
0
100
1
2
3
4
DECELERATION (g)
0
50
100
150
200
0.01 s
1
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a
b
c
FIGURE 2. IMPACT ANALYSIS. The four tracked landmarks (a) on the beak and near the braincase of a pileated woodpecker. (b) This
representative example shows the deceleration of those landmarks. (c) The results of a brain- cavity pressure simulation show that even
the strongest decelerations analyzed in three species of woodpecker— (left to right) black, pileated, and great spotted— yield pressures
that are lower than those in a human brain with the mildest concussion.
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