‘Sandwich’ microstructure of the toucan’s beak provides lightweight stiffness under pressure

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Toucans are unusual among birds for the sheer size of their beaks. Most species fall into two groups, with either short, wide beaks or long, thin ones. Toucans, by contrast, have a long, wide bill which facilitates variety in feeding and makes up a third of their total body length. Although the beak appears cumbersome, it actually only accounts for about 5% of total body mass – thus the bird’s centre of mass remains in line with the wings and so the beak interferes with normal flight mechanics as little as possible. At the same time, the toucan’s bill provides the huge stiffness necessary to feed on tough nuts and it can withstand considerable force. Studies of the beak’s anatomy show that it has an unusual internal structure: the keratinous outer layer of the beak surrounds a fibrous ‘foam’ which lines the beak and a hollow centre. Together, the keratin (which takes the form of staggered ‘scales’) and the fibres which form the foam (identified as a stiffened, calcium-containing protein) can absorb more energy, and withstand greater force, than the sum of the two materials separately. This ‘sandwiching’ strategy, which is also found in porcupine spines and plant stems, allows the central core to absorb some of the force and prevent the outer shell from buckling while – in the case of the toucan – economising on mass. The beak provides one more example of where researchers and developers can take inspiration from biological systems for the production of improved synthetic materials.

Photo courtesy of Ferdy Christant. Read more about this research here.

Keratinous: Made of keratin, the protein which makes up the most part of hair and nails in vertebrates.

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