Helmeted Hornbill

On the list of critically endangered birds is the peculiar-looking helmeted hornbill. The bird inhabits the island of Borneo, the Malay Peninsula, and Sumatra. Its helmet-like structure is called a casque, and it’s mostly the bird’s ivory. The casque is also the reason why poachers hunt the hornbills. They carve out the casque into jewelry and art. 

The hornbills use their casques as a shield when fighting each other over territory or against other predators. These casques account for about 11% of the bird’s estimated 3kg weight, and it’s an almost solid structure.