Casque (anatomy)

In birds, it is an enlargement of the bones of the upper mandible or the skull, either on the front of the face, the top of the head, or both.

The casque has been hypothesized to serve as a visual cue to a bird's sex, state of maturity, or social status; as reinforcement to the beak's structure; or as a resonance chamber, enhancing calls.

[5] In most of these species, the casque is a bony extension of the upper mandible or skull that is covered with a cornified layer of skin.

[7] The structure starts small in youngsters and develops over time, and at maturity is typically larger in males than in females.

[16] Indian grey hornbills casque-butt both in aerial battles, and in clashes between perched and flying birds.

[1] Some theories that have been advanced in the past for cassowary casques – that they provide a "helmet" to protect the birds' heads as they move through the forest, that they serve as a "shovel" during foraging, or that they are used during fights with conspecifics – have now been largely discounted due to a lack of field observations confirming those uses.

Although they are protected by law throughout their range, they are killed at unsustainable rates; between 2011 and 2014, for example, more than 1100 skulls were seized from poachers in Indonesia's Kalimantan region alone.

[2] The veiled chameleon of the arid stretches of southern Saudi Arabia and Yemen has a particularly large casque, which scientists have theorised may be used to collect moisture or store fat.

In the genera Corytophanes and Laemanctus, these modifications are present in both sexes; the thickened bones allow for greater bite strength as there is more area for muscle attachment.