Toucan beaks are built lightweight and strong thanks to a rigid foamy inside and layers of fibrous keratin tile outside.
"The Toucan's beak measures one-third the length of the bird but accounts for a mere one twentieth of its weight (Acta Mater. 2005, 53, 5281). Using electron microscopy, the researchers found that the exterior of the beak is made up of overlapping tiles of keratin, the sulfur-containing fibrous protein that makes up hair, fingernails, and horn. The interior of the beak is constructed of a rigid foam made of a network of calcium-rich bony fibers connected by membranes. The membranes are similar in composition to keratin. Meyers was surprised by the beak's ability to absorb high-energy impacts." (no author 2005:26)
"The toucan beak, which comprises one third of the length of the bird and yet only about 1/20th of its mass, has outstanding stiffness. The structure of a Toco toucan (Ramphastos toco) beak was found to be a sandwich composite with an exterior of keratin and a fibrous network of closed cells made of calcium-rich proteins. The keratin layer is comprised of superposed hexagonal scales (50 µm diameter and 1 µm thickness) glued together. Its tensile strength is about 50 MPa and Young’s modulus is 1.4 GPa. Micro and nanoindentation hardness measurements corroborate these values. The keratin shell exhibits a strain-rate sensitivity with a transition from slippage of the scales due to release of the organic glue, at a low strain rate (5 · 10-5/s) to fracture of the scales at a higher strain rate (1.5 · 10-3/s). The closed-cell foam is comprised of fibers having a Young’s modulus twice as high as the keratin shells due to their higher calcium content. The compressive response of the foam was modeled by the Gibson–Ashby constitutive equations for open and closed-cell foam. There is a synergistic effect between foam and shell evidenced by experiments and analysis establishing the separate responses of shell, foam, and foam + shell. The stability analysis developed by Karam and Gibson, assuming an idealized circular cross section, was applied to the beak. It shows that the foam stabilizes the deformation of the beak by providing an elastic foundation which increases its Brazier and buckling load under flexure loading." (Seki et al. 2005:5281)
Learn more about this functional adaptation.
- 2005. Science Concentrates: Secrets of toucan beak revealed. Chem. Eng. News. 83(50):
- Seki Y; Schneider MS; Meyers MA. 2005. Structure and mechanical behavior of a toucan beak. Acta Materialia. 53(20): 5281-5296.
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