Beak Shape Diverts Impact Forces

a bird with black and white speckled wings, a white body and splotches of red and yellow on its head stands on a wooden stake against a blurry background

Biological Strategy

Golden-fronted woodpecker

AskNature Team

Image: Andy Reago & Chrissy McClarren / Flickr / CC BY - Creative Commons Attribution alone

Manage Impact

An impact is a high force or mechanical shock that happens over a short period of time, such as a hammer hitting a nail rather than a hand pushing slowly against a wall. Because of their speed and force, impacts don’t allow materials to slowly adjust to the force, which can lead to cracks, ruptures, and complete breakage. Therefore, living systems have strategies that can absorb, dissipate, or otherwise survive that force without the need to add large amounts of material. For example, the Toco toucan’s large beak is very lightweight, yet can withstand impacts because it’s made of a composite material with rigid foam inside and layers of a hard, fibrous material outside.

Search this Function

Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

Search this Function

Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

Search this Living System

The beak of the golden-fronted woodpecker protects the brain from trauma by having a shape and material composition that diverts vibrational forces away from the cranial cavity.

[Editor’s Note, 2022: New research from Sam Van Wassenbergh et al. suggests woodpeckers’ “cranial skeleton is used as a stiff hammer to enhance pecking performance, and not as a shock-absorbing system,” and that brains are protected from concussions by their small size. A corresponding update to this page and related pages is pending.]

Species of woodpeckers, such as the golden-fronted woodpecker (Melanerpes aurifrons), 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.

Diagram representing the uneven lengths of the inner and outer beaks of the golden-fronted woodpecker.

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 system of bone, tendon, and muscle surrounding the skull called the hyoid apparatus (read more here). Forces then travel along the hyoid, diverting around the skull and back out through the tongue.

Drawing of a woodpeckers skull with arrows showing forces.

Diagram illustrating the directional influence of forces exerted by the hyoid bone. When the beak strikes a surface, the majority of forces will travel along the upper beak where they will reach the hyoid. Once forces intersect with the hyoid, they will be diverted around the back of the skull and exit through the tongue.

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.

Diagram illustrating the diversion of forces by the lower, inner beak. Forces not absorbed by the upper beak and hyoid will travel through the lower beak where they are absorbed by a sturdy inner beak. Muscle and tissue in the lower jaw will divert forces downward, and away from the brain.

This strategy was contributed by Allison Miller .

Check out these related strategies that collectively protect the woodpecker’s brain from impact:

Last Updated September 3, 2020

References

“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)

Journal article

A mechanical analysis of woodpecker drumming and its application to shock-absorbing systems

Bioinspir. Biomim. | 19/01/2011 | Sang-Hee Yoon, Sungmin Park

embedly preview

Reference

Journal article

Why Do Woodpeckers Resist Head Impact Injury: A Biomechanical Investigation

PLoS ONE | 26/10/2011 | Lizhen Wang, Jason Tak-Man Cheung, Fang Pu, Deyu Li, Ming Zhang, Yubo Fan |

Mark Briffa

embedly preview

AskNature