Contrary to popular belief, woodpeckers do not possess a natural "shock absorber" in their heads.
Woodpeckers often strike trees at speeds of up to 20 kilometers per hour when searching for food, carving nesting holes, or drumming to attract mates and claim territory.
During drumming, they may strike at frequencies of up to 30 times per second. Such rapid deceleration would exceed the threshold for concussions in humans. Many stories, blogs, zoo exhibits, and educational programs have propagated the idea that woodpecker skulls have built-in shock-absorbing structures to protect their brains from damage during high-speed impacts.
Enthusiasts might find comfort in the idea that impact waves traveling from the beak to the brain are cushioned. Over the last decade, with advancements in CT scan reconstruction, researchers have discovered a spongy skeleton structure in the front of the woodpecker's brain. This finding seemed to support the hypothesis that the structure absorbs shock before it reaches the brain.
This porous area, composed of interconnected skeleton rods and plates, was theorized to compress upon impact, reducing forces on the brain. While this theory inspired designs for new shock-absorbing materials and helmets, it had not been thoroughly tested. Additionally, some scientists had expressed skepticism even earlier.
In the 1970s, psychiatrist Philip May and ophthalmologist Ivan Schwab explored the adaptations enabling woodpeckers to withstand repeated impacts, earning an Ig Nobel Prize in 2006 for their work. However, their 1976 paper in The Lancet questioned whether the skull's shock absorption contributed to this resilience. They suggested that if the beak absorbed most of the impact, the bird might need to strike harder to achieve the same effect.
If a bird must accelerate its head forward to gain sufficient kinetic energy for powerful strikes but loses part of that energy to a "built-in" shock absorber, such a mechanism could be evolutionarily disadvantageous.
Why Don’t Woodpeckers Get Concussions?
Video by Be Smart
Investigating the Evidence
Two years ago, an international research team studied three woodpecker species to verify whether a cushioning effect existed between the beak and the brain. High-speed videos recorded the birds' pecking behaviors at four European zoo aviaries, focusing on black woodpeckers and great spotted woodpeckers.
In Canada, two North American black woodpeckers were observed in a laboratory setting. Using video frame analysis, the researchers tracked marked points on the birds’ heads and calculated peak deceleration during strikes, employing a method similar to that used in car crash tests.
Markers included two points on the beak and one on the eye, assumed to move in sync with the skull's front. In some cases, an additional small white marker was applied to the skin over the skull, as seen in the accompanying visuals. Over 100 pecking events were analyzed, comparing deceleration curves for the beak and skull.
The data consistently showed no reduction in skull deceleration compared to the beak, indicating no cushioning effect from spongy skeletons or other mechanisms. The woodpecker's head functions more like a solid hammer than a shock absorber. Biomechanical modeling further confirmed that any potential cushioning within the skull would reduce the beak’s effectiveness at penetrating wood.
Although minimal internal shock absorption might slightly decrease brain deceleration, it would still waste energy. If a bird were to strike less forcefully, it could achieve the same results without expending unnecessary energy. Thus, minimizing cranial shock absorption appears to be an adaptive evolutionary outcome for birds that rely on pecking behaviors.
How Woodpeckers Avoid Injury
If the skull lacks a shock absorption mechanism, how do woodpeckers protect their brains? Data reveals that woodpeckers endure deceleration forces of up to 400 g (gravitational acceleration), well beyond the estimated human concussion threshold of 135 g. In 2006, MIT researcher Lorna Gibson noted that the key lies in the woodpecker’s small size. Smaller brain masses reduce the pressure experienced during deceleration. The brief duration of each strike further enhances their resilience. Additionally, the precise positioning of the brain within the skull minimizes stress during impacts.
The pressure experienced by the brain depends on factors such as deceleration speed, brain tissue density, and brain length (or volume-to-surface-area ratio). In woodpeckers, brain length along the impact direction is approximately one-seventh that of humans. Thus, the concussion threshold for woodpeckers is about seven times higher, roughly 1,000 g. This means even the most intense impacts recorded, around 400 g, fall well within safe limits. The considerable safety margin ensures woodpeckers avoid brain damage even if they accidentally strike harder surfaces than wood. Moreover, the relationship between brain pressure and brain length explains why no giant woodpeckers exist that could carve deeper holes than current species.
Debunking a Widely Accepted Myth
The widespread belief in woodpecker shock absorbers exemplifies how unverified scientific hypotheses can gain traction. Public fascination with the mechanics of head protection and extensive media coverage have likely contributed to the myth's persistence. By providing biomechanical evidence, this research aims to shift perspectives on how woodpeckers truly avoid injury.
