Seeing how a woodpecker repeatedly crashes its face against a tree, it’s hard not to wonder how its brain stays intact.
For years, the predominant theory has been that structures in and around a woodpecker’s skull absorb the shocks created during pecking. “Zoo blogs and information panels present this as a fact: shock absorption is occurring in woodpeckers,” said Sam Van Wassenbergh, a biologist at the University of Antwerp. The picots have even inspired the engineering of shock-absorbing materials and equipment, such as football helmets.
But now, after analyzing high-speed images of woodpeckers in action, Dr. Van Wassenbergh and his colleagues are challenging this long-held belief. They found that woodpeckers do not absorb blows during pecking and are probably not shocked by using their head as hammers. His work was published Thursday in Current Biology.
When a woodpecker hits its beak against a tree, it generates a shock. If something in a woodpecker’s skull was absorbing these shocks before reaching the brain, as a car’s airbag absorbs shocks in an accident before they reach a passenger, then, on impact, the head of a woodpecker would slow down more slowly compared to its beak.
Experimental settings for capturing high speed video. Credit … Van Wassenbergh et al., Current Biology
With this in mind, the researchers analyzed high-speed videos of six woodpeckers (three species, two birds each) climbing a tree. They tracked two dots in each bird’s beak and a dot in their eye to mark the location of their brain. They found that the eye slowed at the same rate as the beak and, in a couple of cases, even faster, which meant that at least the woodpecker did not absorb any shock during the beak.
Dr. Van Wassenbergh said that if woodpeckers absorb some of the shock they were trying to give the tree, “it would be a waste of precious energy for birds. Woodpeckers have undergone millions of years of evolution to minimize the shock absorption “. Maja Mielke, a biologist at the University of Antwerp and co-author of the study, added that, like a hammer, a woodpecker’s skull is “really optimized for pecking performance.”
But with one mystery solved, another emerged: how do the brains of the woodpeckers resist this repeated shock?
To calculate the pressure in the skulls of birds, the researchers created a computational model based on tingling movement and the shape and size of the skull, and found that the pressure created was well below what would cause a concussion in a primate. In fact, birds would have to hit a tree at twice its current speed (or hit the wood four times stiffer) to withstand a concussion. “We forget that woodpeckers are considerably smaller than humans,” Dr. Van Wassenbergh said. “Smaller animals can withstand higher decelerations. Think of a fly hitting a window and then flying again.”
“Traditionally, when people hypothesized how animals work, they often did not even look at the animal alive; they would just pull bones out of a drawer, ”said Michael Granatosky, who studies evolutionary biomechanics at the New York Institute of Technology and did not participate in the study.
Dr. Granatosky sees this work as an example of how much remains to be discovered. “There are all these things we think we know, and we just don’t know,” he said.
But the findings do not answer all the questions about birds, for example, how a woodpecker maintains so much stiffness between its skull and beak during pecking and what other factors may be involved that could mitigate possible brain damage.
“You have to think about the complexity of these systems,” said Ryan Felice, an evolutionary biologist at University College London who did not participate in the study. “It’s not just bones and muscles, but maybe the amount of fluid in the brain and blood pressure, and even the ability to heal damaged neurons.”
Mrs. Mielke sees this work as a call to action for scientists in any field of research. “It’s always worth looking at phenomena that we think we’re already understanding, because sometimes there can be surprises,” he said. “Intuition can deceive us.”