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Beak design absorbs high-energy impacts: toco toucan

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Toucan / Valerie Abbo.. / LicenseCC-by-nc-nd - Attribution Non-commercial No Derivatives

Toucan beaks are built lightweight and strong thanks to a rigid foamy inside and layers of fibrous keratin tile outside.

BIOMIMICRY TAXONOMY
Summary
The structure of the toucan beak teaches us principles of composite material design for light-weight strength and stiffness. Despite its large size (a third of the length of the bird) and considerable strength, the toucan beak comprises only one twentieth the bird’s mass. While the large strong beak is useful in foraging, defense and attracting mates, its low density is essential for the toucan to retain its ability to fly. The beak’s solid outer shell sandwiches within it a closed-cell, foam-like structure made of struts which, together with thin protein membranes, enclose variably shaped air spaces. The solid shell layer is built of overlapping, hexagonally-shaped thin plates of keratin protein held together by an organic glue. The internal closed-cell structural support is comprised of keratin fibers with greater mineralization, by calcium and other salts, than in either the membranes or the solid shell layers to increase hardness. The closed cell structure offers a more complex energy absorption capacity and resistance to compression than the bending deformation typical of open celled structures. The rotational deformation of cell walls, stretching of membranes, and the internal gas pressure all contribute to those features. There is a synergistic effect of the shell layer and foam-like interior elements that together gives it greater strength than the sum of the strengths of those individual parts. Material designs inspired by the structure of the toucan beak could offer the properties of low weight with high stiffness and strength, as well as good energy absorption capacity and insulation value, such as could be useful in developing crash resistance in vehicles without compromising fuel economy.
Excerpt
"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)
About the inspiring organism
Med_tocotoucan Toco Toucan
Ramphastos toco Statius Muller, 1776

Habitat(s): Forest, Grassland
Natural History Information:
SOURCE AND ADDITIONAL INFORMATION FOR NATURAL HISTORY INFORMATION

Animal Diversity Web external link
 
Lorri R. Marek
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Habitat

Ramphastos toco occupies the canopy layer of the tropical rainforest. It avoids dense rainforests,preferring more open habitats, such as woodlands, river forests, plantations, and palm grooves. It is commonly observed near human dwellings and it is abundant throughout its range.

Physical Description

Ramphastos toco is the largest member of its family, which comprises 37 species. It is 25 inches long. The appearance of R. toco is very colorful. Males and females are alike in color and there is no sexual dimorphism (Hanzak and Formanek, 1977). The most outstanding feature of this species of bird is its bill, which is enormous and brightly colored. The bill may be up to 71/2 inches long and is constructed of a honeycomb of bony material. The huge golden-yellow bill looks heavy, but it actually weighs little because it contains many air pockets. The tongue of R. toco is long, narrow, and singularly frayed on each side. This narrow tongue resembles a feather. Each eye is surrounded by an area of bare skin that is usually a brightly-colored orange. The plumage is black except for the white throat. The legs are strong and rather short with large scales. The claws are used for grasping branches. To enable it to grasp the branch, the toucan has two toes point forward and two backward. The tail tends to be long and nearly square. No geographic variation has been reported (Whitfield, 1998).

Behavior

Ramphastos toco is a very noisy member of the jungle society. The bird lives in small communities equivalent to several families. It actively travels in small noisy flocks of half a dozen birds. For only short distances, Ramphastos toco flies gracefully. The bird beats its wings several times and glides. It is more agile in the trees, where it can hop from one branch to another. As with other brightly-colored forest birds, R. toco can hardly be seen, especially when it sits quietly, because its broken patterns harmonize with its surroundings. Its vibrant splashes of color are regarded as a flower or fruit to the eye that notices it. Although the bird's coloring has significant concealing value, R. toco often makes its presence known by its noisy chatter. It has a loud monotonous call that can be heard a half mile away in the jungle (Austin, 1983). This bird is a very playful animal and enjoys a variety of games. One of the favorites is a form of beak wrestling. During the nuptial display, both partners play a game which consists of tossing fruit to each other. After their ritual berry tossing, the birds mate and the female lays her eggs in a nest. Both parents actively take part in caring for the offspring (Skutch, 1996). Although the specific functions of the bill are poorly understood, it may play an important part in the courtship display. As a defensive weapon, the bill serves more as a frightening instrument than as a fighting tool. The bill provides little protection against predators. To escape predation, R. toco hides in a hollow tree. Another interesting behavior of R. toco is the way in which it sleeps. When the bird sleeps, it turns its head so that its long bill rests on its back and the tail is folded over its head. The bird becomes a ball of feathers. Five or six adults may sleep in a single hole, folding their tails over their backs to save space in crowded quarters (Austin, 1983).


Learn more at EOL.org
Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Threat Categories LONG_LC IUCN Red List Status: Least Concern

Bioinspired products and application ideas

Application Ideas: The structure of the toucan's beak could serve as the inspiration for automotive panels that could protect passengers in crashes and could also be used for ultralight aircraft components.

Industrial Sector(s) interested in this strategy: Automotive, aircraft

Experts
Meyers Group
Marc A. Meyers
Department of Mechanical and Aerospace Engineering, University of California San Diego
References
2005. Science Concentrates: Secrets of toucan beak revealed. Chem. Eng. News. 83(50):
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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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Comments

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Sherry
over 5 years ago
Here's a news article about the research: http://www.jacobsschool.ucsd.edu/news_events/releases/release.sfe?id=417
It has some helpful illustrations. Thanks to Michael Alston for sending this link.
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