Why Don't Woodpeckers Get Headaches? How Their Heads Cope

How hard does a woodpecker hit?

A pecking woodpecker swings its head at the wood at several meters per second and stops almost instantly when the bill strikes. Measurements and models suggest decelerations of very roughly 1,000 g, many times what would knock out a person. A busy woodpecker can repeat this thousands of times a day while feeding, digging nest holes and drumming, as described in why do woodpeckers peck wood?

For a long time, that raised an obvious puzzle. If a human footballer or boxer can suffer brain injury from repeated blows, why doesn’t a woodpecker?

The old idea: built-in shock absorbers

The popular answer was that woodpeckers have natural shock absorbers. Writers pointed to the spongy bone in the skull, the slightly flexible bill and the long tongue bones (the hyoid) that wrap around the back of the head, and suggested that together they soaked up the impact like a cycling helmet.

These features are real. Woodpecker skulls do contain plate-like spongy bone concentrated in the forehead and the back of the head, and the hyoid really does loop around the skull. But no one had directly measured whether the head actually absorbs the shock in a living, pecking bird.

What the 2022 study found

A team led by Sam Van Wassenbergh at the University of Antwerp filmed pecking woodpeckers with high-speed cameras, including the black woodpecker of Europe, the North American pileated woodpecker and the great spotted woodpecker. Their results were published in Current Biology in 2022.

The researchers tracked how fast the bill and the eye (a stand-in for the brain) slowed down at each impact. If the head absorbed shock, the eye should have slowed down more gently than the bill. Instead, the head decelerated almost as abruptly as the bill. In other words, the woodpecker’s head behaves like a stiff hammer.

Computer models then showed why this makes sense. A cushioned head would waste much of each blow, so the bird would have to swing harder to chisel the same amount of wood. A stiff head turns more of the energy into useful work on the tree.

So why isn’t the brain damaged?

If the head does not cushion the blows, the brain itself must cope. The leading explanation is size. The forces a brain feels in an impact depend strongly on its mass, and a woodpecker’s brain is tiny, only a few grams even in the largest species. A small brain pressed snugly against the skull experiences much lower stresses than a large human brain sloshing in fluid would at the same deceleration.

Several features help:

The 2022 calculations suggested that during normal pecking, the stress on a woodpecker’s brain stays below thresholds associated with concussion in primates scaled to woodpecker size. Only far harder strikes than the birds normally make would be expected to approach the danger zone.

Do woodpeckers show any brain changes at all?

Probably some. A 2018 study by researchers at Boston University examined preserved brains of woodpeckers from museum collections and found build-ups of tau, a protein associated in humans with brain injury from repeated head impacts, which was not seen in the comparison birds. It is not yet known whether these deposits are harmful in woodpeckers or a normal, perhaps even protective, feature.

That result is a reminder that “woodpeckers never get brain damage” is a stronger claim than the evidence supports. What is clear is that woodpeckers peck all their lives without obvious ill effects.

Other protective tricks

Woodpeckers have several other adaptations that protect them while they hammer:

• A third eyelid, the nictitating membrane, closes just before each strike, shielding the eye from flying chips and possibly helping to hold it in place.
• Slit-like nostrils covered with bristly feathers keep out wood dust.
• A chisel-tipped bill that is kept sharp by use, and strong neck muscles that power each blow.
• Stiff tail feathers that brace the bird against the trunk, so the body takes part of the strain.

The long tongue also helps, though mainly for feeding rather than safety; see how long is a woodpecker’s tongue?

Myths and facts

Myth: the tongue is a seatbelt for the brain. The wrapped-around hyoid is a real and striking structure, but its main job is to let the tongue shoot far out of the bill. Its role in protecting the brain is unproven.

Myth: the skull is a sponge that soaks up every blow. Spongy bone exists, but high-speed measurements show the head does not absorb much shock overall.

Fact: being small is the best protection. At woodpecker size, a stiff head that hits hard is both efficient and safe enough.