Hidden beneath all their rum-pum-pumming, woodpeckers are quietly grunt-grunt-grunting.
The birds exhale with each strike, much like a tennis pro groaning through a stroke. Elaborate coordination between those breaths and muscles across the body keep their hammering at a perfectly consistent rate, researchers report November 6 in Journal of Experimental Biology.
Research into the extraordinary capabilities of woodpeckers — who can strike hundreds of times per minute at forces 20 to 30 times their body weight — has largely focused on how they’re able to percuss without getting concussed. The new analysis simply asks how, at all?
While pecking might look like a simple back-and-forth head motion, “it’s actually a very difficult, skillful behavior that involves the movement of muscles across the body,” says Nicholas Antonson, a behavioral physiologist at Brown University.
Antonson and his colleagues humanely captured eight wild downy woodpeckers (Dryobates pubescens) from the Brown campus and surrounding area. They carefully inserted electrodes into eight different muscles, which measure electrical signals that indicate a muscle’s contraction. Then, for a half hour at a time, the researchers observed the woodpeckers as they drilled (a behavior used to probe and excavate) and tapped (a behavior used to communicate). Each bird wore a tiny custom-fit backpack to record the electrical signals, which the team synced with high-speed video taken at 250 frames per second. After a few days of observation and recovery, the birds were released.
The analysis revealed a complex choreography of muscle and breath that turns the bird into the equivalent of a hammer. When humans use a hammer, the muscles in the back of their wrist stiffen to reduce energy loss at impact; the researchers observed a similar stiffening in some of the woodpecker’s neck muscles. “It’s crazy just how similar it is to the way we hammer,” Antonson says.
Other muscles played distinct roles throughout the striking motion. In the moments preceding, the birds appeared to brace themselves with their tail muscles, whereas the power of the strike itself was largely determined by the activation of a single muscle in the hip. Distinct head and neck muscles help to pull back the head after each beat, activating before other muscles completed their forward movement. The overlapping contractions may help smooth out the peckers’ back-and-forth movements during a rapid drum solo.
The team also looked at airflow through the syrinx — akin to a voice box — to determine whether woodpeckers hold their breath upon a strike, like a weightlifter might, or exhale through the movement, more like a tennis player. Both strategies help stabilize core muscles during a movement — but downy woodpeckers take after tennis players. They can strike and exhale as many as 13 times per second, indulging in a 40-millisecond inhale between each blow. The movement’s timing stayed remarkably consistent over multiple taps, says Antonson.
Songbirds take mini breaths to support their lengthy tunes. That woodpeckers do the same “is suggestive that [tapping] might be more akin to singing than we had realized,” says Daniel Tobiansky, a behavioral neuroscientist who studies birds at Providence College and was not involved in the study. Nonvocal acoustic communication is often overlooked in research of the animal kingdom, he says, and connections like these provide insights into how it may have evolved.
Having taken a “look under the hood” at downy woodpeckers, Antonson plans to continue exploring the mechanics of extreme behaviors performed by other species, to see what insights they might serve up.