When it comes to headbangers, no Black Sabbath fan alive can outdo a woodpecker. Imagine smacking your head into a tree at 15 miles an hour, as frequently as 20 times a second, thousands of times a day, every day. That’s the woodpecker life. Sometimes woodpeckers drill into trees to snack on insects that have bored under the bark. Other times they excavate deep cavities in trees that they nest in. Some species carve cubbyholes in tree trunks to stash acorns. In 2015, an ornithologist filmed a desert woodpecker as it pecked through the skulls of mourning dove chicks to eat their baby brains.
Woodpeckers, despite all this hammering, seem to be fine. Fossils suggest that the birds have been around for 25 million years without concussing themselves to extinction. This has led to the suspicion that the birds don’t suffer head injuries. Woodpeckers might be the closest thing neuropathologists, who are experts in brain trauma, have to a heraldic animal. (Illinois neurosurgeon Julian Bailes, portrayed by Alec Baldwin in the movie “Concussion,” told Forbes he keeps a woodpecker skeleton in his office.)
Yet a new report about woodpecker brain tissue raises the possibility that the birds do suffer some consequences. Maybe the woodpeckers are just fine behaviorally. But they have, to the scientists’ surprise, protein accumulations in their brains that resemble those found in athletes with head trauma.
“No one has actually ever looked at a woodpecker brain to see if it has any neurological issues,” said Peter Cummings, a neuropathologist at Boston University and a self-described “football dad.” Cummings collaborated with two other Boston University scientists: anatomist Don Siwek (who died in December) and neurobiologist George Farah, who performed the lion’s share of the laboratory work.
Farah obtained dead birds from the Harvard Museum of Comparative Zoology and Chicago’s Field Museum. “We were happy to provide the specimens,” said Field Museum evolutionary biologist Ben Marks. The birds were “pickled,” he said, injected with formalin and stored in jars of alcohol for, in some cases, 60 years. “People have looked at brains ever since people have collected birds,” Marks said. But this request was “a little bit different.”
At Boston University, Farah extracted the birds’ brains and sectioned them into paper-thin slices to examine under a microscope. He examined 10 woodpeckers. Five red-winged blackbirds, which do not hammer their heads against trees, provided the control samples.
For each brain slice, Farah stained the tissue with molecules of silver. Silver binds with high specificity to a protein called tau. “Tau is a normal protein in nerve cells,” said Ann McKee, a neuropathologist at Boston University School of Medicine who was not involved with this research.
Tau comes in several types. It typically maintains long, branching structures of nerve cells called axons. But after an injury, tau can change its form and clump up in toxic aggregations. Researchers have found tau in injured humans as well as bears, mice, squirrels and other animals, McKee said.
These tau accumulations are markers of a disease called chronic traumatic encephalopathy, or CTE. CTE, also known as “punch drunk syndrome,” is characterized by aggression, memory loss, confusion and depression, and it can progress to dementia. Autopsies of football players show “overwhelming evidence” that “prolonged exposure to repetitive head impacts” is associated with CTE, McKee said. McKee and her colleagues studied the brains of 111 NFL players. After post-mortem examinations, 110 of the players were diagnosed with CTE.
Tau aggregations are linked to other neurological diseases, too, such as Alzheimer’s. But the protein is not a smoking gun. “It’s not specific for a mechanism of injury, but it’s indicative of something not being right,” Cummings said. There is a wide overlap between what is a normal amount of tau and what is pathological. Tau also accumulates with age.
Farah’s silver stains revealed that none of the red-winged blackbirds, all adults, had tau accumulations. Eight of the 10 woodpeckers did, including a juvenile, the researchers wrote in a report published Friday in the journal PLOS One.
An even more specific chemical stain, which could be used only with three of the bird brains, suggested that the woodpecker accumulations contained the pathological form of tau. The results bore some similarities with human tau staining but were far from identical. “Nevertheless,” McKee said, “it’s an important and provocative finding.”
Cummings and Farah cautioned that it is not possible to conclude these accumulations are toxic. To diagnose CTE in humans, scientists look for accumulations in a specific part of a person’s cerebral cortex.
Woodpecker and human heads are, it should be said, quite different. Human brains slosh more. Our tongues don’t stretch as long as our arms, like woodpecker tongues do, nor do they wrap tightly all the way around our skulls. In 2016, an engineering professor at MIT demonstrated that size matters: Woodpeckers’ small brains make them resilient against deceleration. Human thrill-seekers on amusement park rides experience, at most, an acceleration that is about six times that of the force of gravity, or 6 G. Concussions occur at 90 to 100 G. A woodpecker’s head, when it connects with a tree trunk, decelerates by as much as 1,200 G.
Cummings said it would be a mistake to assume that millions of years of woodpecker adaptation produced physical changes but no cell biology changes. Rather than being signs of trauma, their tau accumulations, after all, might be protective. “It might be a good adaptation,” he said. Or perhaps woodpeckers have some kind of cellular custodians that sweep away excess tau. Humans don’t have that ability — but maybe, Farah said, we could replicate it, if it exists. If this sounds like a lot of speculation — well, they don’t really know what to make of this finding.
We should care about what goes on in woodpecker brains, the authors of the new study said. As you watch 300-pound athletes heave themselves at each other during the Super Bowl on Sunday, consider this: Woodpeckers are helping make football a safer sport. Equipment designers have looked to the birds to inspire protective collars and better helmets. This research suggests woodpeckers have plenty more to teach us about brains, too.