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New understanding of how woodpeckers hammer trees

woodpeckers
High-speed video frames show a Pileated Woodpecker pecking on wood. Researchers from Belgium, France, Canada, and Germany took videos of six individual woodpeckers from three species to study how the birds hammer on trees without causing brain damage. Image credit: Erica Ortlieb and Robert Shadwick/University of British Columbia

One of the great pleasures of winter is listening for drumming woodpeckers. Their loud tattoos ringing out on a frigid, otherwise silent northern landscape fill me with hope that winter will eventually come to an end even as I marvel at the adaptations that allow these splendid birds to slam their faces into solid wood.

Natural selection would obviously favor physiological and morphological modifications protecting woodpeckers from concussions and long-term brain damage. But natural selection must also favor adaptations making their percussive pecks as loud as possible and their hammering as powerful as possible to dig out insects deep in the wood and excavate nesting and roosting cavities. The need for both protection and power would seem to be diametrically opposed.

Traditionally, people have been more focused on under- standing adaptations that protect woodpecker brains than those that make them such mighty hammerers. Indeed, some engineers have incorporated elements of woodpecker anatomy into football helmet designs. One of the most-read articles on BirdWatchingDaily.com, written by the late Eldon Greij in 2013, is titled “Why woodpeckers can hammer without getting headaches,” an overview of the ways scientists have speculated that woodpecker anatomy protects the brain.

But how well-protected is a woodpecker’s brain? In a follow-up column in 2021, “Understanding potential brain damage in woodpeckers,” Greij looked at a 2018 study out of Boston University medical school in which researchers examined woodpecker and blackbird brain tissue for the protein associated with chronic traumatic encephalopathy (CTE) in football players who had suffered repetitive traumatic brain injuries. They found that eight of the 10 woodpeckers examined tested positive for that protein, hyperphosphorylated tau, which is also implicated in some other non- reversible, degenerative conditions in humans, such as dementia, Alzheimer’s disease, and Parkinson’s disease. None of the 10 Red-winged Blackbird brains examined showed evidence of that protein. Might woodpeckers have developed a biochemical mechanism to counteract the effects of it?

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Now, a brand-new study published in Current Biology shows, via extraordinary slow-motion photography, that the woodpecker bill and skull are designed to work as a single unit, a “stiff hammer to enhance pecking performance, and not as a shock-absorbing system to protect the brain.” Looking at specific markers, the study established that the bill and head stopped at exactly the same moment, both experiencing the same force of impact. Speculation that something between the bill and cranium serves as a shock absorber doesn’t hold up.

After my son was in a motorcycle accident, I examined his helmet. The outer shell was cracked, but the inside cushioning had protected his head against injury, unlike his unprotected body. It may be that, as Greij wrote in his 2013 article, much of the protection for a woodpecker’s brain is due to what lies beneath the skull, possibly involving neck muscles, some part of the exceptionally well-developed hyoid apparatus that supports the long tongue by wrapping around the skull, and reduced space in the cranium to decrease the chance of the brain “sloshing around,” exactly as a helmet must fit snugly to protect an athlete or cyclist against head injuries.

This image is a reconstruction of a Black Woodpecker skull from a CT scan. A well-developed zone of spongy bone at the frontal region of the skull, which is hypothesized to absorb shocks, is highlighted in green. Image credit: Christine Böhmer (Christian-Albrechts-Universität zu Kiel) and Anick Abourachid (Muséum National D’Histoire Naturelle)

We have no way of asking woodpeckers how they feel after drumming, so asking why they don’t get headaches may be based on a faulty assumption. We do know that they can have fairly long lives: a banded Pileated Woodpecker is known to have survived at least 12 years, 11 months, and two banded Hairy Woodpeckers have lived over 15 years. How woodpeckers not just survive but apparently thrive with the same protein in their brains related to life-shortening conditions in humans is an important question for both ornithologists and medical researchers.

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The new study, establishing just how exquisitely designed for powerful hammering a woodpecker’s body is, accomplishes what the best scientific research does: it leaves us with more new questions and avenues for research than simple answers. And this study does something more. Watching the researchers’ slow-motion video of a Pileated Woodpecker striking wood, recorded at 1,600 frames per second and shown at 30 frames per second, is as amazing and delightful as it is enlightening.

Watch a video from the woodpecker study

Slow-motion clips of high-speed videos of head impact during pecking by Great Spotted, Pileated, and Black Woodpeckers. The video illustrates the anatomical landmarks that were tracked in the kinematic analysis. Credit: Current Biology/Van Wassenbergh et al

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Laura Erickson

Laura Erickson

Laura Erickson is the 2014 recipient of the American Birding Association’s highest honor, the Roger Tory Peterson Award. She has written many books about birds and hosts the long-running radio program and podcast “For the Birds.” Her column  “Attracting Birds,” about attracting, feeding, sheltering, and understanding the birds in your backyard, appears in every issue of BirdWatching. “Snow Bird,” her first article in the magazine, appeared in December 2003. It described the migration and winter habits of the American Robin.

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