Scientists have debunked the popular theory that a woodpecker can repeatedly hit a tree with its beak at high speed without harming its brain.
The researchers analyzed high-speed videos of three woodpecker species — the spotted woodpecker, black woodpecker, and great spotted woodpecker.
They found that their skulls did not act like shock-absorbing helmets, as previously thought, but rather like hard metal hammers.
In fact, their calculations show that any shock absorption will hinder the woodpecker’s ability to peck.
Woodpeckers quickly drill into trees to reach insects deep in the wood with their long tongues.
An international team of researchers analyzed high-speed videos of three woodpecker species. Here is a sequence of frames from a high-speed pecking video of a spotted woodpecker (Dryocopus pileatus).
Photograph of a black woodpecker (Dryocopus martius) taken during a study at the Alpine Zoo in Innbruck, Austria.
HAMMERS OR HELMETS?
Scientists have long wondered how woodpeckers can repeatedly tap their beak on a tree trunk without damaging their brains.
This led to the idea that their skulls should act as shock-absorbing helmets.
But researchers have challenged this notion, saying their heads act more like hard hammers.
The researchers said that even though their skulls don’t act as shock absorbers, violent pecking doesn’t put their brains at risk.
“After analyzing high-speed videos of three species of woodpeckers, we found that woodpeckers do not absorb the shock of hitting a tree,” said study author Sam Van Wassenberg from the University of Antwerp, Belgium.
When a moving head hits a stationary object, the sudden deceleration of the head (“impact deceleration”) causes compression at the site of impact of the brain and expansion at the back, which can damage neurons and cause dysfunction.
Woodpeckers have a spongy bone in the skull, just in front of the beak, that was previously thought to be a shock absorber.
Developers of cushioning materials and tools such as helmets have even used woodpecker morphology as inspiration.
However, the shock absorber theory is “controversial,” Van Wassenberg and colleagues say, because of “the obvious paradox of shock absorption that the woodpecker wants to pass on to the tree.”
“If the beak had absorbed most of its own impact, the unfortunate bird would have had to fight even harder,” they write in their article.
“Therefore, since strong selective pressure probably improved the mallet’s ability during the evolution of woodpeckers, how could a trait that reduces this performance also evolve?”
Highlighted in green is a well-developed area of cancellous bone in the frontal region of the skull, which presumably absorbs shock.
Van Wassenberg and his colleagues studied the slowing down of the blow during pecking in three species of woodpeckers by filming them and reviewing the footage.
They used the data to build biomechanical models, which led them to conclude that any cranial cushioning would be disadvantageous to them.
Also, while their skulls don’t act as shock absorbers, violent pecking doesn’t put their brains at risk, the researchers say.
While the deceleration shock with each peck exceeds the known concussion threshold in monkeys and humans, woodpeckers’ smaller brains can handle it, they argue.
Van Wassenberg said that woodpeckers can damage their brains if they peck metal with full force.
But their habitual tree trunk pecking tends to be well below the concussion threshold, even if their skulls don’t act as protective helmets.
This contradicts the findings 2018 studywho found that woodpecker brains show high levels of an Alzheimer’s disease-causing protein called tau, which is associated with neurodegenerative diseases such as dementia.
High-speed video footage installed at the University of British Columbia to record the pecking of a hairy woodpecker (Dryocopus pileatus)
According to Van Wassenberg, the lack of cushioning doesn’t mean their brains are in danger during “seemingly hard impacts.”
“Even the strongest blows from the more than 100 ticks analyzed should be brain-safe for woodpeckers, as our calculations showed that brain stress is lower than that of concussion sufferers,” he said.
The findings disprove the longstanding theory of shock absorption that has been popularized in the media, books, zoos, etc.
“While filming woodpeckers in zoos, I have seen parents explain to their children that woodpeckers don’t get headaches because they have a shock absorber built into their head,” he said.
“This myth about the ability of woodpeckers to absorb shock has now been dispelled by our findings.”
The new study was published today in the journal Current biology.