Science

Why woodpeckers don’t mind hitting trees with their faces

Why woodpeckers don't mind hitting trees with their faces
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Watching a woodpecker repeatedly bang its face against a tree, it’s hard not to marvel at how its brain remains intact.

For years, the theory has been that structures in and around a woodpecker’s skull absorb the shock of pecking. “Blogs and bulletin boards in zoos all present this as a fact – that shock absorption occurs in woodpeckers,” he said Sam van Wassenbergh, biologist at the University of Antwerp. Woodpeckers even inspired the technique 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 challenge this long-held belief. They discovered that woodpeckers don’t absorb shock when pecking and are unlikely to get a concussion if they use their head like a hammer. Her work was published in Current Biology on Thursday.

When a woodpecker bangs its beak against a tree, it produces a shock. If something in a woodpecker’s skull absorbed those shocks before they reached the brain—like a car’s airbag absorbs shocks in a crash before they reach a passenger—then a woodpecker’s head would decelerate more slowly than its beak on impact.

Recognition…Van Wassenbergh et al., Current Biology

With this in mind, the researchers analyzed high-speed video of six woodpeckers (three species, two birds each) pounding on a tree. They tracked two spots on each bird’s beak and one spot on its eye to mark the location of its brain. They found that the eye decelerated just as quickly as the beak, and in some cases even faster, meaning the woodpecker—at the very least—didn’t absorb any shock while pecking.

Dr. Van Wassenbergh said that if woodpeckers absorbed some of the shock they were trying to inflict on the tree, “it would be a waste of precious energy for the birds. Woodpeckers have evolved over millions of years to minimize shock absorption.” Maya MielkaBiologist at the University of Antwerp and co-author of the study, added that a woodpecker’s skull, like a hammer, is “really optimized for pecking performance”.

But after one mystery was solved, another emerged: How do woodpecker brains withstand this repeated shock?

To calculate the pressure in the birds’ skulls, the researchers created a computational model based on pecking motion and skull shape and size, and they found that the pressure generated was well below what would cause a concussion in a primate would. In fact, the birds would have to hit a tree twice as fast—or hit wood four times as hard—to suffer a concussion. “We forget that woodpeckers are much smaller than humans,” says Dr. said Van Wassenbergh. “Smaller animals can withstand higher decelerations. Think of a fly that hits a window and then just flies back.”

“Traditionally, when people hypothesized how animals work, most of the time they didn’t even look at the live animal; They would just pull bones out of a drawer,” he said Michael Granatsky who studies evolutionary biomechanics at the New York Institute of Technology and was not involved in the study.

DR. Granatosky regards this work as an example of how much remains to be discovered. “There’s all these things that we think we know and we just don’t know,” he said.

But the results don’t answer all questions about the birds — for example, how a woodpecker maintains such rigidity between its skull and beak when pecking, and what other factors might be involved that might mitigate potential damage to the brain.

“You have to think about the complexity of these systems,” he said RyanFelice, an evolutionary biologist at University College London who was not involved in the study. “It’s not just about bones and muscles, but maybe also the amount of fluid in the brain and blood pressure and even the ability to heal damaged neurons.”

MS. Mielke sees this work as a call to action for scientists in all research areas. “It’s always worth looking at phenomena that we think we already understand, because sometimes surprises can happen,” she said. “Intuition can deceive us.”

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