When you watch a woodpecker repeatedly bang its face against a tree, it’s hard not to wonder how its brain stays intact.
For years, the prevailing theory has been that structures in and around a woodpecker’s skull absorb the shocks generated during pecking. “Blogs and information panels in zoos present all this as fact – that shock absorption occurs in woodpeckers,” said Sam Van Wassenbergh, a biologist at the University of Antwerp. Woodpeckers have even inspired the development of shock-absorbing materials and equipment, such as football helmets.
But now, after analyzing high-speed footage of woodpeckers in action, Dr. Van Wassenbergh and colleagues this long-held belief. They found that woodpeckers don’t absorb shock when pecking, and they are unlikely to get concussions from using their heads as hammers. Their work was published Thursday in Current Biology.
When a woodpecker hits a tree with its beak, it causes a shock. If something in a woodpecker’s skull absorbs these shocks before they reach the brain – as a car’s airbag absorbs shocks in an accident before reaching a passenger – then a woodpecker’s head would decelerate more slowly in a crash compared to its beak.
With this in mind, the researchers analyzed high-speed videos of six woodpeckers (three species, two birds each) hammering into a tree. They traced two points on each bird’s beak and one point on its eye to mark the location of its brain. They found that the eye slowed down at the same rate as the beak and in a few cases even faster, meaning that — at the very least — the woodpecker didn’t absorb any shock while pecking.
dr. Van Wassenbergh said that if woodpeckers absorbed some of the shock they were trying to deliver to the tree, “it would be a waste of precious energy for the birds. Woodpeckers have undergone millions of years of evolution to minimize shock absorption. ” Maja Mielke, a biologist at the University of Antwerp and a co-author of the study, added that a woodpecker’s skull is “really optimized for pecking performance,” much like a hammer.
But as one mystery was solved, another emerged: How do woodpecker brains withstand that repeated shock?
To calculate the pressure in the birds’ skulls, the researchers created a computer model based on pecking movements and skull shape and size, and they found that the pressure created was much lower than what would cause a concussion in a primate. In fact, the birds would have to hit a tree at twice their current speed — or hit wood four times as hard — to sustain a concussion. “We forget that woodpeckers are significantly smaller than humans,” said Dr. Van Wassenbergh. “Smaller animals can handle higher delays. Think of a fly hitting a window and then just flying back.”
“Traditionally, when people came up with hypotheses about how animals function, they often never even looked at the living animal; they would just pull bones out of a drawer,” said Michael Granatosky, who studies evolutionary biomechanics at the New York Institute of Technology and was not involved in the study.
dr. Granatosky considers this work an example of how much remains to be discovered. “There’s all these things that we think we know, and we just don’t know,” he said.
But the findings don’t answer all questions about the birds — for example, how a woodpecker maintains such stiffness between its skull and beak while pecking, and what other factors may play a role that may reduce potential brain damage.
“You have to think about the complexity of these systems,” said Ryan Felice, an evolutionary biologist at University College London who was not involved in the study. “It’s not just bones and muscles, but maybe the amount of fluid in the brain and blood pressure, and even the ability to heal damaged neurons.”
Ms. Mielke sees this work as a call to action for scientists in every field of research. “It’s always worth looking at phenomena that we think we already understand, because sometimes there can be surprises,” she said. “Intuition can fool us.”