The ultimate strength of woodpecker's cranial bone was found to be markedly higher than that of the lark. In contrast, there was no significant difference between the two birds in the ultimate strengths of their beaks. More plate-like spongy bone was present in the cranial bone of the woodpecker, while the cranium of the lark contained more rod-like structures. It appears that the mechanical properties and microstructure are closely linked. The larger number of plate-like structures, greater thickness and numbers of trabeculae, and the closer spacing between individual trabeculae in the woodpecker cranial bone would tend to resist deformation during pecking, which would decrease the stress on the brain. Conversely, the greater quantity of rod-like structures and thinner trabeculae of the woodpecker's beak would lead to greater deformation during impact. As the impact load is absorbed and distributed primarily by the beak, its transmission to the brain would be decreased. Together these parameters combine to produce quite similar ultimate strengths of the beaks of the woodpecker and the lark.
It was concluded that, compared with the lark, the cranial bone of the woodpecker achieves a higher ultimate strength and resistance to impact injury as a result of its unique microstructure, including more plate-like trabecular bone, greater thickness, greater numbers and closer spacing of trabeculae, and a higher proportion of bone mineral. These distinctive mechanical and structural properties, and compositions, of the cranial and beak bones of the woodpecker provide excellent resistance to head impact injury at a high speed and deceleration. Such information may perhaps inspire the design and optimization of protective headgear for humans.
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Science in China Press