Belgian researchers have disproved the popular hypothesis that the structure of the woodpecker’s skull absorbs shocks to the tree trunk. On the contrary, the woodpecker’s head has evolved to increase pecking efficiency rather than protect the brain. In doing so, the size and shape of the cranium provide the intracranial pressure at which the woodpecker’s brain is safe.
Scientists have long wondered how woodpeckers don’t get a concussion when they bang their heads against a tree trunk. Researchers believed that their skull structure must somehow cushion the impact. This hypothesis remained paradoxical, because any absorption or dissipation of kinetic energy from the head by the skull would probably impair the bird’s ability to chisel wood, so it would be unlikely to appear in the evolutionary process.
Now scientists from the University of Antwerp (Belgium) have refuted this assumption and shown that woodpeckers’ heads look more like hard hammers than protective helmets. The results of the study are published in the journal Current Biology.
The authors analyzed high-speed video recordings of woodpeckers of three species (Dendrocopos major, Dryocopus pileatus and Dryocopus martius) hammering the bark of trees. Scientists have quantified the deceleration of impact during pecking for the first time and developed biomechanical models of the skulls of these birds. The results showed that the head of woodpeckers was optimized for pecking efficiency and not at all for brain protection, as any cushioning of the skull would be extremely unprofitable and energy-consuming for them.
The question then arose as to why such dynamic pecking did not harm the woodpeckers’ brains. If a human or a monkey had been in the bird’s place, concussion would have been assured. Scientists then conducted numerical simulations of how the size and shape of the cranium affects intracranial pressure.
It turned out that the pressure kept the woodpecker’s brain safe even with severe blows, because the force on it was lower than what would cause a concussion in primates. However, these birds can still suffer cranial trauma – for example, if they mistakenly start pounding metal with all their might.
The findings refute the popular hypothesis about cranial shock absorption. If it were true, the evolutionary process would probably have produced woodpeckers with much larger heads and strong neck muscles. But in this case, their brains and skulls would have reached such a size that strikes would have become unsafe.
The results have some practical implications, too, as engineers have previously used the anatomy of the woodpecker cranial skeleton as a source of inspiration in designing shock-absorbing materials and helmets. Given that woodpecker anatomy minimizes shock absorption, this may not be the best idea.