Woodpeckers operate at an extreme level, boring through solid wood with forces more than 30 times their own weight and drilling up to 13 times a second. How do they never miss a beat while head banging so hard?
It turns out that the birds tense up their entire body to smash through wood, letting out short, explosive grunts with each strike, report Brown University biologist Nicholas Antonson and his colleagues in the Journal of Experimental Biology. “Woodpeckers really are nature’s hammer in a sense,” Antonson says.
To study how the birds tap, the researchers first humanely captured eight wild Downy Woodpeckers and carefully inserted electrodes into their muscles in the laboratory. The electrodes fed into a tiny, fitted backpack that recorded electrical signals from contracting muscles as the birds pecked. They also checked whether the woodpeckers held their breath during exertion (like weight lifters tend to do) or exhaled (like tennis players) while striking the wood by examining airflow through the birds’ air sacs—small, balloonlike structures that help them breathe in and out. By matching these measurements with high-speed videos, the scientists tracked the woodpeckers’ taps down to every four milliseconds.
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Instead of using a single muscle to control the action, woodpeckers activated “every muscle from the head to the tail,” Antonson says. The birds used their powerful hip flexors to push forward, clenched their tail and abs to prepare for the strike, and stiffened the back of their head and neck on contact—similar to the way you might stiffen the back of your wrist when you hammer a nail. They then engaged a different set of hip and neck muscles to draw back.
The birds also perfectly paired their pecks with sharp exhalations “as another means of stabilizing their core muscles and powering through those strikes,” Antonson explains. “To be able to breathe out 13 times per second and inhale on the order of 40 milliseconds is really impressive.” Songbirds, which aren’t closely related to woodpeckers, are the only other birds known to so precisely time their breaths, which they do as they sing.
“Pecking is a full-body exercise,” says University of Alabama biologist Nicole Ackermans, who studies brain damage in woodpeckers and head-butting sheep. Coordinating “micro breaths” with muscle clenching and creating “this hammerlike structure in their whole body is such a unique approach,” she adds.