Scales, sutures and porosity help the birds hammer without going stupid
Damage control is in the details. Tiny structures in a woodpecker’s beak help the bird hammer furiously without turning its brain to mush.
The birds can strike a tree 100 to 300 times a minute, decelerating each time with a jolt around a thousand times stronger than the pull of gravity. The structure of woodpeckers’ heads has already inspired designs for shock absorbers. And now Lakiesha Williams and colleagues at Mississippi State University have found damage-control measures in the beak itself, they report May 7 in the Journal of the Royal Society Interface.
The outside layer of the beak of a red-bellied woodpecker (Melanerpes carolinus) consists of tiny scales of the protein keratin. The woodpecker’s scales are thinner, more elongated and appear in greater numbers than scales covering the beaks of toucans, the researchers found. Woodpecker keratin scales maximize the friction of rubbing against each other and thereby dissipate energy from an impact.
Also, the grains of keratin making up the scales border each other with wavy sutures. Long, wavy sutures can resist a compressing force, and woodpecker sutures are at least three times as wavy as toucans’ and chickens’ sutures.
The innermost layer of a woodpecker beak, the bone, is less porous than beak bones in chickens and toucans. That lower porosity helps create the difference in beak layers that guides the shockwave toward a safe path through the head.
Editor's Note: This article was updated June 11, 2014, to correct the porosity of woodpecker beaks relative to those of chickens and toucans.
N. Lee et al. Hierarchical multiscale structure-property relationships of the red-bellied woodpecker (Melanerpes carolinus) beak. Journal of the Royal Society Interface. Published May 7, 2014. doi: 10.1098/rsif.2014.0274.
S-H. Yoon and S. Park. A mechanical analysis of woodpecker drumming and its application to shock-absorbing systems. Bioinspiration & Biomimetics. Vol. 6, January 17, 2011, p. 016003. doi: 10.1088/1748-3182/6/1/016003.
R. Cheung. Insects covered in tough stuff. Science News Online, April 12, 2012.