Woodpeckers spend all day hammering their head on tree trunks, using their beak to make holes and digging insects out of those holes for a meal. The birds’ distinctive drumming and drilling had led researchers to hypothesize that the bone between woodpeckers’ beak and braincase must absorb shocks to protect their brain from concussions. But a new study suggests that their head and beak act like a stiff hammer for optimal pecking performance rather a shock-absorbing system to cushion the brain.
“What this bird has to do during the entire day is dig holes into the wood. It’s very important that this business be very efficient,” explains Sam Van Wassenbergh, an evolutionary biomechanicist at the University of Antwerp in Belgium, who led the new study. If the woodpecker absorbs some of the energy it directs at the tree, then less energy is imparted to the tree trunk, and it has to peck even harder to make holes. “So the more you think about it, the less it made sense that there was any shock absorption going on,” Van Wassenbergh says. “But it had to be tested.”
So how do woodpeckers avoid concussions? The researchers used simulations to calculate the impact on the brains of the birds and compared it with thresholds for concussion-causing forces in humans. For people, an impact of about 135 g’s produces a concussion. But woodpeckers are much smaller. The length of their brain is about one seventh that of a human, which means that they can withstand forces that are seven times higher, Van Wassenbergh explains. Based on the models, the forces woodpeckers’ brain sustains are below the danger threshold by a factor of two. So “they could hit the tree at higher speeds and still not suffer a concussion,” he says. “The key is that the head of the woodpecker is just much smaller than that of a human.”
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