Scientists have debunked a popular theory that the woodpecker can repeatedly strike a tree with its beak at high speed without causing brain damage to itself.
Researchers analyzed high-speed video of three species of woodpecker – crested woodpecker, black woodpecker and great spotted woodpecker.
They found that their skulls do not act like shock-absorbing helmets as previously thought, but rather like stiff metal hammers.
In fact, their calculations show that any shock absorption would affect the woodpeckers’ ability to peck.
Woodpeckers quickly burrow into trees to use their long tongues to extract insects from deep within the wood.
An international team of researchers analyzed high-speed video footage of three woodpecker species. Here is an image sequence from a high speed video showing the Helmeted Woodpecker (Dryocopuspileatus) being pecked.
Photo of a Black Woodpecker (Dryocopus martius) taken in the study room of Alpenzoo Innsbruck, Austria
HAMMERS OR HELMETS?
Scientists have long wondered how woodpeckers can repeatedly bang their beaks against tree trunks without damaging their brains.
This led to the notion that their skulls should act like shock-absorbing helmets.
But researchers have refuted that notion, saying their heads appear more like stiff hammers.
Although their skulls don’t act as shock absorbers, the angry pecking doesn’t endanger their brains, the researchers said.
“By analyzing high-speed video of three woodpecker species, we found that woodpeckers do not absorb the shock of impact with the tree,” said study author Sam Van Wassenbergh of the University of Antwerp, Belgium.
When a moving head impacts a stationary object, the head’s sudden deceleration (an “impact deceleration”) causes compression at the impact site of the brain and expansion at the back, which can damage neurons and cause dysfunction.
Woodpeckers have a spongy bone in their skull, just in front of their beak, previously identified as a shock absorber.
Engineers of shock absorbing materials and tools like helmets have even used the morphology of woodpeckers as a source of inspiration.
However, the shock absorber theory is “controversial,” say Van Wassenbergh and his colleagues, due to an “apparent paradox of absorbing the shock the woodpecker wants to apply to the tree.”
“If the beak had absorbed much of its own impact, the unfortunate bird would have to strike even harder,” their paper said.
“Since strong selective pressure has likely enhanced batting performance through woodpecker evolution, how can a trait that decreases that performance have evolved as well?”
The well-developed zone of cancellous bones at the front of the skull, which is believed to absorb shock, is highlighted in green
Van Wassenbergh and colleagues studied the impact delays during pecking in the three woodpecker species by filming them and looking back at the footage.
They used the data to build biomechanical models, leading them to conclude that any shock absorption of the skull would be detrimental to them.
Even though their skulls don’t act as shock absorbers, the angry pecking doesn’t endanger their brains, the researchers say.
While the deceleration shock with each pick exceeds the known threshold for concussion in monkeys and humans, the woodpeckers’ smaller brains can withstand it, they claim.
Van Wassenbergh said woodpeckers could risk brain damage if they pecked at metal with full force.
But their usual log pecking is generally well below the threshold to inflict concussion, even if their skull doesn’t act as a hard hat.
This contrasts with the findings of a 2018 study that found woodpecker brains to have high levels of an Alzheimer’s-causing protein called tau, which has been linked to neurodegenerative diseases like dementia.
High-speed video recording facility at the University of British Columbia to record pecking by the Helmeted Woodpecker (Dryocopuspileatus).
According to Van Wassenbergh, the lack of shock absorption doesn’t mean her brain is in danger during what appear to be violent shocks.
“Even the strongest shocks from the more than 100 picks analyzed should still be safe for the woodpecker’s brain, as our calculations have shown that the brain load is lower than that of people who suffer a concussion,” he said.
The results refute the long-held theory of shock absorption popularized in the media, books, zoos and more.
“While filming the woodpeckers in zoos, I’ve seen parents explain to their children that woodpeckers don’t get headaches because they have shock absorbers built into their heads,” he said.
“This shock absorption myth in woodpeckers is now shattered by our results.”
The new study was published today in the journal Current Biology.
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