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A male Downy woodpecker.

A variety of evolutionary adaptations allow woodpeckers to drill their beaks into trees at a force of 1,200 to 1,400 g’s thousands of times per day without any apparent brain damage or other adverse effects.

But, until now, the brains of woodpeckers had never been examined for evidence of neurological damage, so the actual consequences of this repetitive impact have remained unknown.

A trio of researchers from Boston University are now investigating how woodpeckers’ brains handle the stress and prevent damage.

The researchers used bird brains from collections at the Field Museum and Harvard Museum of Natural History – 10 of which were Downy woodpecker specimens and five were red-winged blackbirds used as a control group. Some of the specimens were originally collected in the 1960s and have been well preserved in the museum for 50 years.

The team was specifically looking to see if the bird brains contained any buildup of tau – a protein associated with brain damage and neurodegenerative diseases in humans.

Tau proteins can actually be helpful in stabilizing brain cells, but an excess amount of tau buildup can disrupt neurons from communicating with one another, according to the researchers.

"When the brain is damaged, tau collects and disrupts nerve function -- cognitive, emotional, and motor function can be compromised," said Peter Cummings, study author.

Tau buildup has been linked to Alzheimer’s and chronic traumatic encephalopathy (CTE), among other neurodegenerative diseases. More recently, athletes involved in soccer, hockey and football have become the focus of CTE research, as it is believed repetitive hits to the head and concussions can lead to tau buildup, and eventually CTE.

A major study published in July 2017, also from Boston University, found that 110 of 111 former NFL players analyzed had evidence of CTE. Unfortunately, the disease can typically only be diagnosed post-mortem.

But the skulls of woodpeckers endure a force that is 14 times more than the amount of force known to cause concussions in humans – and the animals can peck at trees more than 10,000 times a day. The birds have even been used as inspiration in designing innovative safety gear for athletes.

For the study, published in PLOS ONE, the researchers removed thin slices of brain tissue from the bird specimens and stained them with silver ions to highlight the presence of tau proteins.

The results showed that eight of the 10 woodpeckers had an accumulation of tau proteins, while none of the red-winged blackbirds in the control group had any observable buildup.

“The anatomic locations and staining patterns of the lesions identified in the brains of woodpeckers shares some similarities to human CTE,” wrote the study authors.

Tau buildup can sometimes occur in humans as part of the normal aging process, but the researchers ruled out that this could be a factor for the woodpeckers. One of the woodpeckers examined was a juvenile, and still showed the full spectrum of tau accumulations seen in the adult population. Additionally, all the control birds were adults, and showed no evidence of build-up.

Despite the evidence of tau buildup in the woodpeckers, the researchers still note that it may not necessarily be a sign of brain damage in the birds like it would be in humans.

"The earliest woodpeckers date back 25 million years -- these birds have been around for a long time," said Cummings. "If pecking was going to cause brain injury, why would you still see this behavior? Why would evolutionary adaptations stop at the brain? There's possibility that the tau in woodpeckers is a protective adaptation and maybe not pathological at all."

Some of the woodpecker adaptations that are believed to better handle the intense daily impact include thick neck muscles and sharp beaks with upper and lower components that can move independently of each other. The birds’ brains are also tightly situated within their skill, which limits any bouncing or movement.

“The continued study of the response of the woodpeckers’ brain to pecking is necessary to assure current head protection technology based on the woodpecker model is providing adequate protection in athletes. Our findings also suggest the woodpecker may be a suitable animal model for the further study of CTE,” the authors conclude.

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