Species of woodpeckers, such as the golden-fronted woodpecker, drum with their beak to establish their territories and attract mates. The high-speed pecking motion causes a tremendous amount of stressed force on the animal. However, the woodpecker has a specialized beak that helps to prevent physical and neurological trauma by diverting forces away from the brain. Its beak will absorb and divert forces 2-8 times greater than that of the skull.
The beak is comprised of two layers—an interior layer of strong, dense bone, and an exterior layer of flexible tissue matter. While the exterior layer of the upper beak is slightly longer than that of the lower beak, X-ray imaging shows that the interior layer of the lower beak is slightly longer than its upper counterpart.
This diagram represents the uneven lengths of the inner and outer beaks of the golden-fronted woodpecker. Illustration by Allison Miller.
The exterior layer is the first to encounter any impact forces. The flexible tissue allows the upper beak to bear high amounts of stress and reduces the risk of shock by bending and flexing with each vibrational transmittance.
Once forces reach the hard bone, the upper beak intersects with a thin bone surrounding the skull called the hyoid bone (read more here). Forces then travel along the hyoid bone, diverting around the skull and back out through the tongue.
This diagram illustrates the directional influence of forces exerted by the hyoid bone. Illustration by Allison Miller.
As forces continue to travel along the beak, those that have not been diverted by the upper beak encounter the inner-lower beak. Following the path of least resistance, vibrational forces follow the downward slope of the beak’s shape down and away from the cranial space.
This diagram illustrates the diversion of forces by the lower, inner beak. Forces not absorbed by the upper beak and hyoid bone travel through the lower beak, where they are absorbed by a sturdy inner beak. Muscle and tissue in the lower jaw diverts forces downward, away from the brain. Illustration by Allison Miller.
Check out these related strategies that collectively protect the woodpecker’s brain from impact:
“The woodpecker’s beak…is a specialized chisel effective in cutting into a tree; unlike a human-made chisel, the beak is self-sharpening…; the beak, made of elastic material, is relatively large compared to the body. This endoskeletal feature prevents incident mechanical excitations [i.e., the impact] of drumming from directly reaching the brain. [Another shock-absorbing] feature is a hyoid which rigidly supports the tongue. This musculotendinous tissue serves as an attachment site for the muscles around the throat and tongue…[and] encompasses the head…This feature, not seen in other birds, aids the woodpecker in extending its tongue in order to evenly distribute [the impact] from drumming and to reinforce the head—in other words, the hyoid bypasses the vibrations generated from drumming. [Another shock-absorbing] feature, a spongy bone, which is specially located at the contrecoup position from the beak, allows the woodpecker to avoid brain damage (May et al 1976a, 1976b). This bone is relatively dense but spongy compared to other bones…The spongy bone is thought to evenly distribute incident mechanical excitations [the drumming impact] before they reach the brain…Finally, a skull bone with CSF [cerebrospinal fluid] plays…a key role in dissipating mechanical excitations from drumming…[T]he woodpecker has a very narrow space for CSF between the skull bone and brain. This bird therefore has…relatively little CSF, thereby reducing the transmission of the mechanical excitations into the brain through the CSF (May et al 1976a, 1976b, Schwab 2002).” (Yoon and Park 2011:3)