Woodpeckers repeatedly whack their heads against trees with a force 10 times that of a concussion-inducing football tackle, yet they seem no worse for the wear. That has inspired some athletic companies to model helmets and neck collars on the head-banging birds. But woodpeckers may not be immune to head trauma after all. A new study shows that a protein whose abnormal buildup is considered a sign of human brain damage also accumulates in woodpecker brains. That raises an intriguing question: Could the newly discovered “tangles” of this protein, tau, be protecting the woodpecker brain from injury?
The idea of concussionless woodpeckers dates back to 1976, when a seminal study that examined sections of the birds’ brains found no evidence of injury. That research spurred “a cascade of papers” on woodpecker biomechanics and their force-resisting adaptations, says George Farah, a neurobiologist at Boston University. Because the old study used an outdated staining method to reveal damage in the brain, he and his colleagues decided to redo the work with 21st century technology.
They asked several museums for woodpecker specimens whose brains they could study. Their final haul: six downy woodpeckers, one yellow-bellied sapsucker, one northern flicker, one pale-billed woodpecker, and one lineated woodpecker. For comparison, they also got five brains from a non–head-banging species, the red-winged blackbird.
After sectioning the brains, the researchers stained them to detect potentially pathogenic deposits like tau, which may play a role in chronic traumatic encephalopathy (CTE) and other neurodegenerative diseases, including Alzheimer’s. Eight of the 10 woodpecker brains came back positive for deposits—but all of the blackbirds’ came back negative. What’s more, the deposits were in the front of the brain, the same place where tau accumulates in people with CTE.
To figure out whether the deposits were in fact tau, the researchers stained all 10 woodpecker brains with a tau-specific antibody. The method didn’t work for seven of the brains. But in the remaining three, two tested positive, the team reports today in the journal PLOS ONE. That shocked Peter Cummings, a neuropathologist at Boston University and one of Farah’s co-authors. “I assumed that woodpeckers didn’t have tau accumulation in their brains, just like everybody in the research world had and the athletic equipment world had,” he says.
But that doesn’t mean the woodpeckers are brain-damaged. “All tau roads in head impact do not lead to CTE,” says Douglas Smith, a neurotrauma researcher at the University of Pennsylvania. In fact, some tau is good because the protein, which exists inside of cells, helps stabilize neurons and keep their shape-retaining structures intact. But head trauma can dislodge the tau, creating deposits that clog up the brain.
It’s not clear how much tau can accumulate in a woodpecker brain before the bird starts behaving abnormally, says Shannon Hackett, an evolutionary biologist at the Field Museum in Chicago, Illinois. (For Hackett, such research is personal: Her son plays ice hockey.) Cummings says that more work is also needed to figure out whether the tau in woodpecker brains is an adaptation for dealing with head trauma, or whether the birds have ways of dissolving excess accumulations of tau. He notes that woodpeckers have neck muscles and cranial bone structures that protect them from the 1200 Gs of force—that is, 1200 times the force of gravity—they sustain while pecking. “Why would those adaptations stop at the brain?”
If they haven’t, woodpecker research could illuminate how other head-banging animals protect themselves from brain trauma—and perhaps inspire new ways to protect vulnerable National Football League players.