Woodpeckers hit trees with their beaks many times a day. For a long time, people believed their heads worked like soft cushions. But in 2022, scientists filmed woodpeckers with fast cameras. Their heads stopped as suddenly as their beaks.

So the head works like a hard hammer. A soft head would make it hard to make holes. Woodpeckers may be safe because their brains are small.

Woodpeckers hammer trees with their beaks, and it was long believed that their skulls absorbed the shock like a cushion. This idea even inspired designs for helmets. In 2022, Sam Van Wassenbergh and his team in Belgium filmed three species of woodpecker with high-speed cameras. If the head absorbed shock, the area around the eyes should stop more slowly than the beak.

Instead, both stopped almost at the same moment. The researchers explained that a shock-absorbing head would actually weaken pecking, just as a hammer wrapped in rubber cannot drive a nail well. According to their calculations, the birds avoid concussions mainly because their brains are small, which reduces the stress on the brain.

It has long been claimed that a woodpecker's skull acts as a natural shock absorber, an idea that has influenced the design of helmets and protective materials. In 2022, however, Sam Van Wassenbergh and colleagues questioned the logic behind it: a head that absorbed impact would also waste the energy needed to chisel into wood, much as a rubber-coated hammer drives nails poorly. Filming black woodpeckers, pileated woodpeckers, and great spotted woodpeckers at high speed, they compared the deceleration of the beak with that of the eye region and found virtually no difference, meaning the head behaves as a stiff hammer.

Their models suggested that pressure inside the bird's small brain stays below levels associated with concussion in primates. This agrees with Lorna Gibson's 2006 analysis, which attributed the bird's safety to its small brain, the brevity of each impact, and the brain's orientation within the skull. The story has a twist, though. In 2018, a team found deposits, including tau protein, in the brains of eight of ten preserved woodpeckers. Whether this represents harm or adaptation is unknown, the sample was small, and applying primate concussion thresholds to birds may not be valid.