Watching a woodpecker repeatedly banging its face against a tree trunk, it’s hard not to wonder how its brain remains so intact.
For many years, the prevailing theory was that the structures in and around the woodpecker’s skull absorb the shocks generated during pecking. “Blogs and bulletin boards at zoos all show this as true – that shock absorption is happening in woodpeckers,” says Sam Van Wassenbergh, a biologist at the University of Antwerp. Woodpeckers even inspired ‘s technique shock absorbing material and equipment, such as football helmets.
But now, after analyzing high-speed footage of woodpeckers in action, Dr Van Wassenbergh and colleagues are challenging long-held beliefs. They found that woodpeckers do not absorb shocks during pecking, and that they are able to avoid shocks when using their heads like hammers. Their work has been published in Current biology on Thursday.
When a woodpecker hits a tree with its beak, it creates a shock. If something in the woodpecker’s skull absorbs these shocks before they reach the brain – the way a car’s airbag absorbs shocks in a crash before they reach the passenger – on impact, the woodpecker’s head will decelerate more slowly than its beak.
With this in mind, the researchers analyzed high-speed video of six woodpeckers (three species, two of each) slamming into a tree. They tracked two points on each bird’s beak and one point on their eyes to mark where their brains were. They found that the eye decelerates at the same rate as the beak and, in some cases, even faster, which means that – at least – the woodpecker doesn’t absorb any shock in surgical process.
Dr. Van Wassenbergh said that if woodpeckers absorb some of the shock they are trying to transmit to the tree, “it would be a waste of precious energy for the birds. Woodpeckers have undergone millions of years of evolution to minimize shock absorption.” Maja MielkeA biologist at the University of Antwerp and a co-author of the study, added that like a hammer, the woodpecker’s skull is “really optimized for pecking performance”.
But with one mystery solved comes another: How does a woodpecker’s brain withstand that repeated shock?
To calculate the pressure in the skulls of the birds, the researchers created a computational model based on pecking movements and the shape and size of the skull, and they found that the pressure generated was low. far more than what can cause tremors in a primate. In fact, the birds would have to hit a tree at twice their current speed – or hit hard wood four times as much – to withstand the concussion. “We forget that woodpeckers are significantly smaller than humans,” says Dr. Van Wassenbergh. “Smaller animals can tolerate higher deceleration. Think of a fly hitting a window and then flying back again.”
“Traditionally, when people hypothesize about how animals work, they’ve never even looked at live animals; they’ll just pull the bones out of the drawer,” Michael Granatosky who studies evolutionary biomechanics at the New York Institute of Technology and was not involved in the study.
Dr. Granatosky sees this work as an example of how much remains to be discovered. “There are all sorts of things we think we know, and we don’t,” he said.
But the findings don’t answer all avian questions – for example, how does a woodpecker maintain such stiffness between its skull and beak while pecking, and what other factors are involved? Other factors that may be involved may minimize possible brain damage.
“You have to think about the complexity of these systems,” says Ryan Felice, an evolutionary biologist at University College London, who was not involved in the study. “It’s not just bones and muscles, but possibly brain fluid levels and blood pressure, and even the ability to heal damaged nerve cells.”
Ms. Mielke sees the work as a call to action for scientists in any field of research. “It is always valuable to look at phenomena that we believe we understand, because sometimes, there can be surprises,” she said. “Intuition can deceive us.”