The iconic sound of a woodpecker drumming against a tree trunk might seem like a simple action, but new research reveals a sophisticated interplay of muscles and breath that allows these birds to perform feats of incredible force. While most studies have focused on how woodpeckers avoid brain injury during repeated impacts, this latest analysis, published in the Journal of Experimental Biology, explores why they are able to hammer at all, uncovering a process remarkably similar to human hammering.
A Full-Body Effort
Woodpeckers can strike hundreds of times per minute with forces 20 to 30 times their body weight. However, this isn’s just a repetitive head motion. “It’s actually a very difficult, skillful behavior that involves the movement of muscles across the body,” explains Nicholas Antonson, a behavioral physiologist at Brown University. Underneath their recognizable “rum-pum-pumming” is a quieter “grunt-grunt-grunting” – the sound of the birds exhaling with each strike, much like a tennis player groaning through a stroke.
Tracking Woodpecker Movement
To understand this complex system, Antonson and his colleagues captured eight wild downy woodpeckers (Dryobates pubescens) from the Brown University campus and surrounding areas. They strategically inserted electrodes into eight different muscles, which measured electrical signals indicating muscle contraction. During 30-minute observation periods, the woodpeckers were observed drilling (used for probing and excavating) and tapping (used for communication), while wearing tiny, custom-fit backpacks recording electrical signals synchronized with high-speed video filmed at 250 frames per second. After a few days of observation and recovery, the birds were released.
Similarities to Human Hammering
The research uncovered a precise choreography of muscle and breath that transforms the bird into a highly efficient hammering machine. Like humans stiffening wrist muscles to minimize energy loss when hammering, the researchers observed a similar stiffening in some of the woodpecker’s neck muscles. Specifically, they found:
- Tail Muscles for Bracing: Birds brace themselves just before a strike using their tail muscles.
- Hip Muscle Power: The power of the strike is primarily determined by a single muscle in the hip.
- Head and Neck Muscle Coordination: Distinct head and neck muscles pull the head back after each beat, contracting before other muscles complete the forward movement, smoothing out the rapid drumming.
The Role of Breath
The researchers also investigated airflow through the syrinx (the bird’s voice box) to determine if woodpeckers hold their breath during impacts or exhale through the movement. Similar to weightlifters, holding breath stabilizes core muscles during a movement—but downy woodpeckers opted for a tennis player’s approach. They can strike and exhale up to 13 times per second, inhaling for a brief 40-millisecond period between each blow. Remarkably, this timing remained consistent across multiple taps.
Implications for Understanding Bird Communication
The study’s findings suggest that drumming may be more akin to singing than previously understood. Songbirds use mini-breaths to support their lengthy tunes. Downy woodpeckers engaging in a similar practice provides insights into the evolution of non-vocal acoustic communication, a domain often overlooked in animal kingdom research.
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.
The research highlights the complexity and elegance of the woodpecker’s hammering, demonstrating that even seemingly simple behaviors involve a sophisticated coordination of muscles and breath. This novel look at woodpecker mechanics provides valuable insights into animal physiology and communication, furthering our understanding of the natural world.
