Woodpeckers grunt and brace their bodies like athletes to maximize drilling power

Woodpeckers pack a punch, pounding wood with extreme force and experiencing decelerations of up to 400g. Now, researchers reveal in the Journal of Experimental Biology that drilling woodpeckers turn themselves into hammers by bracing their head, neck, abdomen and tail muscles to hold their bodies rigid when they pound on wood, driving each impact with the hip flexor and front neck muscles.

In addition, they discovered that the birds synchronize their breathing with their movements each time they strike wood, like ace tennis stars that grunt noisily to stabilize core muscles when they take a shot. The research team included Nicholas Antonson, Matthew Fuxjager, Stephen Ogunbiyi, Margot Champigneulle and Thomas Roberts (all at Brown University, U.S.) and bird song expert Franz Goller (University of Münster, Germany).

To find out how woodpeckers use their muscles when drilling, the team gently caught eight wild downy woodpeckers and filmed the birds with high-speed video over 3 days, recording when they drilled and tapped on a piece of hardwood.

In addition, the scientists measured electrical signals in the birds’ head, neck, abdomen, tail and leg muscles, to determine when they contracted as the birds pounded with their beaks.

The researchers also recorded the air pressure in a section of the airway of six birds and the amount of air two of them exhaled through their voice boxes, to track their breathing before returning the birds to their homes in the wild.

Piecing together the information, the team realized that the hip flexor and the front neck muscles are essential, propelling the birds forward as they drive their beaks into the wood.

“At the same time, other muscles appear to play supportive roles,” says Antonson, explaining that the birds tipped their heads back and braced with three muscles situated at the base of the skull and back of the neck.

In addition, the birds steadied their bodies with their abdominal muscle, and they also prepared for impact by flexing the tail muscle, before using it to stabilize the hip to anchor the body against the tree at the moment of impact.

Essentially, downy woodpeckers brace their bodies to turn themselves into a hammer to drive their beaks into wood.

But woodpeckers aren’t just one-hit wonders, the birds fine-tune the power of their impacts, depending on whether they are drilling hard or tapping more softly to send a message. The team compared the strength of the muscle contractions as the woodpeckers pecked and found that the front hip flexor muscle contracted harder while the birds were drilling—driving the harder impact—easing off when they tapped more softly.

Finally, the team focused on the woodpeckers’ breathing patterns, noticing that the birds exhaled forcefully, as if grunting, at the instant that the beak struck wood.

“This type of breathing pattern is known to generate greater co-contraction of trunk musculature,” says Antonson, adding that grunting effectively boosts the power of each blow.

The team also realized that the birds perfectly synchronized their breathing with each impact as they tapped more softly at rates of up to 13 strikes per second, inhaling a mini-breath (~40 ms) between each rapid blow.

Woodpeckers use their entire bodies when drilling and tapping like a hammer, from the tip of their beaks to their tails, but unlike tennis players, their grunts are drowned out by the drumming.