The woodpecker is like a hammer, constantly beating hard trees. It not only finds food by woodpecking, but also relies on it to dig holes in the trunk to build a nest, but also relies on it to communicate and demonstrate with each other. Woodpecking is one of the most important activities of woodpeckers. It can peck 12000 times a day, with a frequency of 20 times per second. The deceleration force of each impact is 1200 times that of gravity, which is equivalent to hitting the wall at a speed of 25 kilometers per hour. If humans act like woodpeckers, there is no doubt that they will lead to a series of fatal consequences, such as concussion, brain injury, retinal hemorrhage and retinal detachment. How do woodpeckers avoid these?
The woodpecker’s brain is relatively small, and the surface area of small objects is relatively large. The pressure exerted on it is easy to disperse, so it is not as prone to concussion as the human brain. When the woodpecker pecks wood, the knocking direction is very vertical, which can avoid meningeal tear and concussion caused by the torque caused by shaking.
Woodpeckers have also evolved a series of devices to protect the brain and eyes from impact. Its skull is very thick, but there are many small gaps in the bone, a bit like a sponge, which can reduce the vibration. There is a membrane on the surface of the brain called pia mater, and there is a membrane called arachnoid outside it. There is a cavity between the two membranes called subarachnoid cavity. The human subarachnoid space is filled with cerebrospinal fluid. But the woodpecker’s subarachnoid space is very narrow and there is almost no cerebrospinal fluid, which weakens the fluid transmission of shock waves.
Woodpeckers have cartilage at the bottom of their jaws to cushion impact. Its lower jaw is connected with the skull by a powerful muscle. Before the impact, this muscle contracts rapidly and also acts as a buffer, allowing the impact force to pass to the bottom and rear of the skull and bypass the brain.
The eye structure of woodpeckers is also very clever. The high-speed camera shows that the blink film of the woodpecker’s eyes will close quickly at the moment before the impact, which not only prevents the wood chips splashed by the impact from damaging the eyes, but also wraps the eyes like a safety belt to prevent the eyes from jumping out. The choroid in its eyes fills the gap with a mucopolysaccharide, which can act as a buffer. There is a comb membrane like a comb on the eyelids of birds, which may also play a shockproof role, because once it is congested, it can temporarily increase intraocular pressure and protect the lens and retina.
The most wonderful thing is the woodpecker’s tongue. Its tongue is very long. It grows from the back of the upper jaw, passes through the right nostril, forks into two, then goes around the upper and rear of the skull, passes through both sides of the neck and the lower jaw, and forms another tongue in the mouth. Such a tongue is like a rubber band, which can shoot 10 cm out of the beak. Obviously, the main purpose of this long tongue is to hook insects out of the hole, but if the tongue shrinks before each woodpecking, it can absorb the impact force and is also a good buffer device.
Darwin repeatedly lamented the cleverness of the woodpecker’s body structure in the origin of species. He wrote: “can we give a more moving example of this adaptability when the woodpecker climbs trees and catches insects from the cracks in the bark?” but the woodpecker’s body structure is even more exquisite than that envisaged by Darwin. Biologists’ study of such body structure is not funny at all, nor is it purely out of academic curiosity, nor is it of no practical value.
The body structure of woodpecker is the result of long-term evolution under the action of natural selection. It is an experiment done by nature for millions of years. Studying how it skillfully avoids the body damage caused by impact is not without inspiration for improving the protective equipment to prevent human brain damage.