Every time a woodpecker's beak strikes wood, the brain suffers an apparent catastrophic impact.
"When you see these birds in action, hitting their heads against a tree quite violently, we as humans start wondering how this bird avoids getting headaches or brain damage," says Sam Van Wassenbergh, a researcher at the Belgium's University of Antwerp.
Scientists have previously proposed that the bird's brain is protected from impacts by a cushioned skull, a beak that absorbs some of the force, or a tongue that wraps around the brain.
Van Wassenberg, on the other hand, was not convinced.
"Nobody, in my opinion, has ever explained it very well," he says.
So Van Wassenbergh led a team that set out to solve the problem by filming woodpeckers in action at high speeds.
"We went to four different zoos in Europe with woodpeckers and recorded them at very high frame rates while they pecked," he says.
The videos, which were part of a study published in Current Biology, revealed some remarkable details.
Van Wassenbergh explains that "they close their eyes at the moment they impact the wood" to protect their eyes from splinters.
The videos also revealed that woodpecker beaks frequently become stuck in the wood. They break free almost instantly, thanks to a clever beak design that allows the upper and lower beaks to move independently.
The videos did not show any indication that the woodpecker's brain is cushioned in any way.
"The way we see the head behaving is very rigid, like hitting the wood with a hammer," Van Wassenbergh says.
That is, the organ is subjected to repeated deceleration, which would result in a concussion in a human brain. Even after thousands of impacts in a single day, the woodpecker brain remains unharmed.
According to Van Wassenbergh, this is possible because a woodpecker's brain is protected — not by cushioning, but by its small size and weight.
"A smaller animal can withstand higher decelerations," he explains. "That's a law of biomechanics."
Lorna Gibson, an MIT professor of biomechanical engineering, proposed this idea in 2006. Van Wassenbergh's high-speed video has now confirmed it.
The brain of a woodpecker is approximately 700 times smaller than that of a human. "As a result, even the hardest hits we observed are unlikely to result in a concussion," Van Wassenbergh says.