Hidden beneath all their rum-pum-pumming, woodpeckers are quietly grunt-grunt-grunting.

The birds exhale each time they strike their beaks against tree bark. The sound is similar to a tennis player’s grunt while hitting a ball. Woodpeckers match those exhales to their muscle movements. And that keeps them pecking at a surprisingly steady rate.

The finding comes from a November 6 study in Journal of Experimental Biology.

Woodpeckers are famous for hammering away at trees really fast and really hard. They strike wood hundreds of times per minute at forces 20 to 30 times their body weight. Until now, most research has focused on how woodpeckers do this without hurting their heads. The new research simply asked: How do woodpeckers do this at all?

No easy task

Pecking might look like a simple back-and-forth motion. But “it’s actually a very difficult, skillful behavior,” says Nicholas Antonson. It involves “the movement of muscles across the body,” he says. Antonson studies animal behavior at Brown University in Providence, R.I.

He was part of a team that used a special kind of net to gently capture eight wild downy woodpeckers (Dryobates pubescens). They collected these birds from the Brown campus and surrounding area.

To learn about the birds’ movements, the scientists inserted electrodes into their muscles. Those devices picked up small electrical signals as the birds’ muscles contracted, or shortened. Each bird wore a tiny backpack that recorded the electrode data. At the same time, a camera captured high-speed video of the birds’ movements.

The researchers watched the woodpeckers for a half hour at a time. They saw the birds drill, a behavior used to poke and dig. They also observed the birds tapping to communicate. After a few days, the scientists released the birds back into the wild.

Hammering away

A close look at the electrode and video data showed that woodpeckers’ muscles and breathing work in harmony. This allows the birds’ heads to move like hammers.

When humans use a hammer, muscles in the back of their wrist stiffen. That cuts how much energy is lost when they hit something. The researchers saw a comparable stiffening in some of the woodpeckers’ neck muscles. It’s amazing, Antonson says, “just how similar it is to the way we hammer.”

Other muscles played special roles in the pecking motion. Before they struck, the birds seemed to steady themselves with their tail muscles. The power of the strike itself came from a single muscle in the hip.

Distinct head and neck muscles helped pull back the head after each beat. These muscles activated before others completed their forward movement. The overlapping contractions may help smooth out the peckers’ back-and-forth motions during a rapid drum solo.

The team also looked at the woodpeckers’ breathing to see if they exerted effort more like weightlifters or tennis players. Heavy weightlifters hold their breath when flexing. Tennis players, meanwhile, exhale through big movements.

Downy woodpeckers, it turned out, take after tennis players. They can jab and exhale as many as 13 times per second. Between each blow, the birds take an inhale that lasts just 40 milliseconds. That’s 10 times faster than some humans blink! The movement’s timing stayed remarkably consistent over multiple taps, Antonson reports.

Bird’s-eye view

Songbirds are known to take mini breaths while singing. Woodpeckers doing the same thing suggests their pecking, when done socially, might be more like singing than experts had thought, says Daniel Tobiansky. He wasn’t involved in the new study. He studies bird brains and behavior at Providence College in Rhode Island.

Nonvocal communication, such as pecking, often gets overlooked in animal research, Tobiansky says. Finding a similarity between bird drumming and singing might help scientists learn how these behaviors evolved.