During mating season, male hornbills reportedly use their casqued bills
for spectacular head-on collisions in mid-air.
A month or more before mating, the male hornbill begins courting the female by bringing her food. When ready to lay her eggs, the female will enter a nest hole high in a hollow tree. The pair will then spend two or three days plastering up the hole with the female’s clay-like droppings — she on the inside, he on the outside — using the sides of their bills as trowels.
The female will remain enclosed for three months as the male delivers food to her and then to the chicks through a small finger hole. She will go through a complete molt of her flight feathers while ensconced in the nest; once the nestlings have gotten their first feathers, she will break out of the chamber and join her mate in provisioning food for their young.
Hornbills appear to pair for life, bonding together to defend a territory against other members of their species. This helps to ensure adequate food supply as well as “exclusive rights” to nesting sites.