Tuesday, December 29, 2015

Woodpeckers and Concussions

According to an essay in The Federalist,
The average woodpecker hits its beak against a tree at an estimated 15 miles an hour, 20 times per second, about 12,000 times a day. According to physicists, for the bird, that is an equivalent of coming to a complete stop every second from 26,000 miles per hour. This happens every day over the woodpecker’s lifespan. In g-force—the force exerted using mass, weight, acceleration, and gravity—a woodpecker can withstand 1,200 g. Yet the birds do not suffer any head injuries or brain trauma.

In comparison, the average National Football League hit has two players colliding between 100 to 150 g, often experiencing concussions that register when impact reaches 80 to 100 g. How then, is it possible that a tiny bird can withstand ten times the impact as a human...?
Well, Matt Soniak at Mental Floss has an answer to that question. I've borrowed some of it here:
First, a woodpecker’s skull is built to absorb shock and minimize damage. The bone that surrounds the brain is thick and spongy, and loaded with trabeculae, microscopic beam-like bits of bone that form a tightly woven “mesh” for support and protection. On their scans, the scientists found that this spongy bone is unevenly distributed in woodpeckers, and it is concentrated around the forehead and the back of the skull, where it could act as a shock absorber.

Woodpeckers' hyoid bones act as additional support structures. In humans, the horseshoe-shaped hyoid is an attachment site for certain throat and tongue muscles. Woodpeckers’ hyoids do the same job, but they’re much larger and are differently shaped. The ends of the “horseshoe” wrap all the way around the skull and, in some species, even around the eye socket or into the nasal cavity, eventually meeting to form a sort of sling shape. This bizarre-looking bone, the researchers think, acts like a safety harness for the woodpecker’s skull, absorbing shock stress and keeping it from shaking, rattling and rolling with each peck.

Inside the skull, the brain has its own defenses. It’s small and smooth, and is positioned in a tight space with its largest surface pointing towards the front of the skull. It doesn’t move around too much, and when it does collide with the skull, the force is spread out over a larger area. This makes it more resistant to concussions, the researchers say.

A woodpecker’s beak helps prevent trauma, too. The outer tissue layer of its upper beak is longer than the lower beak, creating a kind of overbite, and the bone structure of the lower beak is longer and stronger than the upper one. The researchers think that the uneven build diverts impact stress away from the brain and distributes it to the lower beak and bottom parts of the skull instead.

The woodpecker’s anatomy doesn’t just prevent injuries to the brain, but also its eyes. Other research using high-speed recordings has shown that, in the fraction of a second just before their beaks strike wood, woodpeckers’ thick nictitans—membranes beneath the lower lid of their eyes, sometimes called the “third eyelid”—close over the eyes. This protects them from debris and keeps them in place. They act like seatbelts, says ophthalmologist Ivan Schwab, author of Evolution's Witness: How Eyes Evolved, and they keep the retina from tearing and the eye from popping right out of the skull.

There’s also a behavioral aspect to the damage control. The researchers found that woodpeckers are pretty good at varying the paths of their pecks. By moving their heads and beaks around as they hammer away, they minimize the number of times in a row that the brain and skull make contact at the same point. Older research also showed that the strike trajectories, as much as they vary, are always almost linear. There’s very little, if any, rotation of the head and almost no movement immediately after impact, minimizing twisting force that could cause injury.
Very interesting, but I have a question for Matt. Early on in his piece on woodpecker adaptations he says this:
In an average day, a woodpecker does this [bangs its head against a tree] around 12,000 times, and yet they don’t seem to hurt themselves or be the least bit bothered by it. This is because, after millions of years of this type of behavior, they’ve evolved some specialized headgear to prevent injuries to their heads, brains, and eyes.
My question is how did they survive for millions of years before the requisite anatomical equipment evolved? Imagine primitive human beings coming to think that banging their heads against a brick wall will somehow help them find food. It would seem that they'd all quickly give up the behavior or else go extinct long before they evolved the cranial structures to mitigate the damage they were doing to themselves. That woodpeckers have obviously not gone extinct, that they've evolved all these marvelous adaptations through sheer blind luck, is testimony to the stupefyingly miraculous powers and wonders of Darwinian naturalism. Or God.

Lewis' Woodpecker