Why woodpeckers don’t mind hitting trees with their faces

Watching a woodpecker repeatedly smash its face against a tree, it’s hard not to wonder how its brain remains intact.

For years, the prevailing theory has been that the structures in and around a woodpecker’s skull absorb the shocks created during pecking. “Blogs and information boards in zoos all present this as a fact – that shock absorption happens in woodpeckers,” said Sam Van Wassenbergh, a biologist at the University of Antwerp. The spikes have even inspired the engineering of shock-absorbing materials and equipment, such as football helmets.

But now, after analyzing high-speed images of spikes in action, Dr. Van Wassenbergh and his colleagues are challenging that long-held belief. They found that woodpeckers don’t absorb shock during pecking, and they probably don’t get a concussion from using their head like a hammer. Their work was published Thursday in Current Biology.

When a woodpecker slams its beak against a tree, it generates a shock. If something in a woodpecker’s skull absorbed those shocks before they reached the brain – the same way a car’s airbag absorbs shocks in an accident before they reach a passenger – then, upon impact, a woodpecker’s head would decelerate more slowly than its beak.

Credit…Van Wassenbergh et al., Current Biology

With that in mind, the researchers analyzed high-speed videos of six woodpeckers (three species, two birds each) pounding a tree. They tracked two dots on each bird’s beak and a dot on its eye to mark the location of its brain. They found that the eye decelerated at the same rate as the beak and, in a few cases, even faster, which meant – at the very least – that the peak did not absorb any shock during pecking.

Dr Van Wassenbergh said if the woodpeckers absorbed some of the shock they were trying to transmit to the tree, ‘it would be a waste of precious energy for the birds. The picks have undergone millions of years of evolution to minimize shock absorption. Maja Mielke, a biologist at the University of Antwerp and co-author of the study, added that, like a hammerhead, a woodpecker’s skull is “really optimized for pecking performance”.

But once one mystery is solved, another emerges: how does the woodpecker brain resist this repeated shock?

To calculate the pressure in the birds’ skulls, the researchers created a computer model based on the pecking motion and the shape and size of the skull, and they found that the pressure created was far below what would cause a concussion. in a primate. In fact, birds would have to hit a tree at twice their current speed – or hit wood four times harder – to suffer a concussion. “We forget that woodpeckers are considerably smaller than humans,” said Dr Van Wassenbergh. “Small animals can withstand greater decelerations. Think of a fly that hits a window and then comes back. »

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

Dr. Granatosky considers this work an example of how much there is yet to discover. “There are all these things that we think we know, and we just don’t know,” he said.

But the results don’t answer all the questions about birds – for example, how a woodpecker maintains such rigidity 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 was not involved 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.”

Ms. 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 already understand, because sometimes there can be surprises,” she said. “Intuition can deceive us.”

Sharing is caring!

Leave a Reply

Your email address will not be published.