Hornbills

Hornbills are birds found in tropical and subtropical Africa, Asia and Melanesia of the family Bucerotidae. They are characterized by a long, down-curved bill which is frequently brightly coloured and sometimes has a horny casque on the upper mandible. Hornbills have a two-lobed kidney. They are the only birds in which the first and second neck vertebrae (the atlas and axis respectively) are fused together; this probably provides a more stable platform for carrying the bill. The family is omnivorous, feeding on fruit and small animals. They are monogamous breeders nesting in natural cavities in trees and sometimes cliffs. A number of mainly insular species of hornbill with small ranges are threatened with extinction, mainly in Southeast Asia.

In the Neotropical realm, toucans occupy the hornbills' ecological niche, an example of convergent evolution. Despite their close appearances, the two groups are not very closely related, with toucans being related to several families of barbet, while hornbills (and their close relatives, the ground hornbills) are allied with the hoopoes and wood-hoopoes.