Hornbill

The casque

The hornbill’s most distinctive feature is the casque — a hollow or foam-filled projection atop the bill, which varies from a small ridge to an enormous structure larger than the bill itself. The great hornbill’s casque is bright yellow and gold; the rhinoceros hornbill’s curves dramatically upward in an orange-and-red crescent.

The casque’s function is debated: amplification of calls, display for mate selection, and as a jousting weapon in males fighting over territory have all been proposed. In the helmeted hornbill, the casque is solid ivory-like keratin — tragically making it a target for illegal trade comparable to elephant ivory.

The sealed nest

Most hornbills practice one of the most extraordinary nesting behaviors in birds: the female enters a tree cavity, and both birds seal the entrance with mud, droppings, and food — leaving only a narrow slit through which the male passes food. The female remains sealed inside, incubating and raising chicks, for up to 4 months. She molts her flight feathers during this period, becoming completely flightless.

The male feeds the family throughout — a demanding commitment for large species. If the male is killed, the female and chicks usually die.

Frugivores and seed dispersers

Most hornbills are primarily frugivorous, and many tropical forests depend on hornbills as long-distance seed dispersers. A single great hornbill may carry and deposit seeds kilometers from the parent tree. Forests where hornbills have been hunted out show reduced regeneration of many tree species.