The Truth About Woodpeckers

The average woodpecker smashes its beak against a hard surface more than 10,000 times a day. Any human who jolted their head like this would likely end up with a concussion. This traumatic brain injury is caused by a blow to the skull. So why doesn’t the constant hammering turn woodpeckers’ brains into mush?

For years, it was assumed that woodpeckers had some kind of cushioning in their heads to protect their brains during pecking. Many scientists suggested that spongy bone in the birds’ skulls absorbed and lessened the shock of each impact (see Myth Buster: Hard Headed). This idea was repeated in scientific articles, in textbooks, and on informative plaques at zoos. Even though the concept “is often presented like a clear-cut fact, there haven’t been any real tests to prove it,” says Sam Van Wassenbergh. He’s a biologist who studies biomechanics, or how living things move, at the University of Antwerp in Belgium.

Woodpeckers smash their beaks against hard surfaces. The average woodpecker does this more than 10,000 times a day. Picture any human hitting their head like this. They would likely end up with a concussion. This traumatic brain injury is caused by a blow to the skull. But woodpeckers are constantly hammering. So why don’t their brains turn into mush? 

For years, scientists assumed that woodpeckers had some kind of cushioning in their heads. It protected their brains during pecking. Many scientists suggested that the birds’ skulls contained spongy bone. They thought it absorbed and lessened the shock of each impact (see Myth Buster: Hard Headed). This idea was repeated in scientific articles and textbooks. It even appeared on signs at zoos. Even though the concept “is often presented like a clear-cut fact, there haven’t been any real tests to prove it,” says Sam Van Wassenbergh. He’s a biologist at the University of Antwerp in Belgium. He studies biomechanics, or how living things move.

When you think about it, says Van Wassenbergh, the shock-absorbing skull idea doesn’t make much sense. A woodpecker drills into wood in search of insects to eat. When the bird’s head accelerates forward, the movement generates kinetic energy. This energy of motion is transferred to the tree when the bird slams its beak against the trunk. If a woodpecker’s skull had cushioning, it would absorb some of this energy and decrease the force of the peck. Why would a bird that survives by pecking evolve to do it less effectively? Van Wassenbergh and his team decided to see what was really going on.

Think about it and the shock-absorbing skull idea doesn’t make much sense, says Van Wassenbergh. A woodpecker drills into wood to find insects to eat. The bird’s head speeds forward, and the movement produces kinetic energy. This energy of motion transfers to the tree when the bird’s beak slams against the trunk. A cushioned skull would absorb some of this energy. That would decrease the force of the peck. Woodpeckers survive by pecking. So why would they evolve to peck less effectively? Van Wassenbergh and his team decided to see what was really happening.

First, the researchers recorded videos of woodpeckers’ heads in motion. To capture this rapid movement, the scientists needed special high-speed cameras. Each peck lasts only a fraction of a second!

Van Wassenbergh’s team recorded videos of six woodpeckers from three species and analyzed the footage. The researchers used a computer to track three points on each bird’s head: one on the skull and two on the beak. The scientists hypothesized that if the birds’ skulls had shock absorbers, the footage would show a “squishing” of the space between the skull and beak—like when a spring compresses. But that didn’t happen. Instead, the birds’ heads moved as one stiff unit, like a hammer.

Next, the team wanted to demonstrate why this adaptation would be helpful to the birds. Using computer models, the scientists simulated woodpecker skulls with and without shock absorbers. Then the researchers compared the force of the pecks. “The pecking performance was greatly reduced in the skull with a shock absorber,” says Maja Mielke, a biologist who worked on the study. With shock absorbers, says Mielke, “the poor birds would need to pound even harder to reach the same results.” For a woodpecker, having a shock-absorbing skull would simply be a waste of energy.

First, the researchers made videos of woodpeckers’ heads in motion. Each peck lasts only a fraction of a second. The scientists used high-speed cameras to record this rapid movement.

Van Wassenbergh’s team chose six woodpeckers from three species. The team recorded and studied videos of the birds. A computer tracked three points on each bird’s head. One was on the skull and two on the beak. The scientists hypothesized what would happen if the birds’ skulls had shock absorbers: In the videos, the space between the skull and beak would appear to squish. It would act like a spring compressing. But that’s not what happened. Instead, the birds’ heads and beaks moved as one stiff unit. They acted like a hammer.

Why would this adaptation help the birds? The team wanted to show that next. So they made computer models of woodpecker skulls with and without shock absorbers. Then the researchers compared the force of the pecks. “The pecking performance was greatly reduced in the skull with a shock absorber,” says Maja Mielke, a biologist who worked on the study. With shock absorbers, “the poor birds would need to pound even harder to reach the same results,” says Mielke. So a shock-absorbing skull wouldn’t help a woodpecker. It would simply waste energy.

If woodpeckers’ skulls don’t absorb shock, then why doesn’t constant pecking damage the birds’ brains? To answer this question, the researchers calculated how harmful the blows from pecking actually are. It turns out the hits aren’t that dangerous because the birds’ brains are so small. “Small masses can tolerate stronger impact forces without being damaged,” says Mielke. “Think about how a housefly can hit a window over and over again without injuries, while a human would suffer quite a bit if they ran into a window at the same speed.” 

Busting this well-known woodpecker myth meant a lot to Van Wassenbergh and his colleagues. They hope their research will help change this widely held belief. “It was surprising to realize that we misunderstood the function of the woodpecker skull for such a long time,” says Mielke. “This experiment just shows that it is still worth having a closer look at things we think we already understand.”

The team concluded that woodpeckers’ skulls don’t absorb shock. So why doesn’t constant pecking damage the birds’ brains? To find out, the researchers calculated the effects of pecking. How harmful are the blows? They found that the hits aren’t that dangerous, because the birds’ brains are so small. “Small masses can tolerate stronger impact forces without being damaged,” says Mielke. “Think about how a housefly can hit a window over and over again without injuries, while a human would suffer quite a bit if they ran into a window at the same speed.” 

So Van Wassenbergh’s team helped bust a well-known woodpecker myth. That means a lot to them. They hope their research will help change this widely held belief. “It was surprising to realize that we misunderstood the function of the woodpecker skull for such a long time,” says Mielke. “This experiment just shows that it is still worth having a closer look at things we think we already understand.”