Hornbill

The hornbills (Bucerotidae) are a family of bird found in tropical and subtropical Africa, Asia and Melanesia. They are characterized by a long, down-curved bill which is frequently brightly colored and sometimes has a casque on the upper mandible. Both the common English and the scientific name of the family refer to the shape of the bill, 'buceros' being 'cow horn' in Greek. 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 species of hornbill are threatened with extinction, mostly insular species with small ranges. Hornbills show considerable variation in size, ranging from the black dwarf hornbill (Tockus hartlaubi), at 102 grams (3.6 oz) and 30 cm (1 ft) in length, to the great hornbill (Buceros bicornis), at up to 4 kg (8.8 lb) and 1.2 m (3 ft 11 in) in length. Males are always bigger than the females, though the extent to which this is true varies according to species. The extent of sexual dimorphism also varies with body parts. For example, the difference in body mass between males and females is 1–17%, but the variation is 8–30% for bill length and 1–21% in wing length. The most distinctive feature of the hornbills is the heavy bill, supported by powerful neck muscles as well as by the fused vertebrae. The large bill assists in fighting, preening, constructing the nest, and catching prey. A feature unique to the hornbills is the casque, a hollow structure that runs along the upper mandible. In some species it is barely perceptible and appears to serve no function beyond reinforcing the bill. In other species it is quite large, is reinforced with bone, and has openings between the hollow centre, allowing it to serve as a resonator for calls. In the helmeted hornbill the casque is not hollow but is filled with hornbill ivory and is used as a battering ram in dramatic aerial jousts. Aerial casque-butting has also been reported in the great hornbill. The plumage of hornbills is typically black, grey, white, or brown, and is frequently offset by bright colours on the bill, or by patches of bare coloured skin on the face or wattles. Some species exhibit sexual dichromatism, where the coloration of soft parts varies by gender. Hornbills possess binocular vision, although unlike most birds with this type of vision, the bill intrudes on their visual field. This allows them to see their own bill tip and aids in precision handling of food objects with their bill. The eyes are also protected by large eyelashes which act as a sunshade. The Bucerotidae include about 55 living species, though a number of cryptic species may yet be split, as has been suggested for the red-billed hornbill. Their distribution includes Sub-Saharan Africa and the Indian Subcontinent to the Philippines and the Solomon Islands, but no genus is found in both Africa and Asia. Most are arboreal birds, but the large ground hornbills (Bucorvus), as their name implies, are terrestrial birds of open savanna. Of the 24 species found in Africa, 13 are birds of the more open woodlands and savanna, and some occur even in highly arid environments; the remaining species are found in dense forests. This contrasts with Asia, where a single species occurs in open savanna and the remainder are forest species. The Indian subcontinent has 10 species of hornbills, of which 9 are found in India and adjoining countries, while the Sri Lanka grey hornbill is restricted to the island. The most common widespread species in the Indian subcontinent is the Indian grey hornbill.According to the International Union for Conservation of Nature (IUCN), Indonesia has 13 hornbill species: 9 of them exist in Sumatra, and the rest exist in Sumba, Sulawesi, Papua and Kalimantan. Kalimantan has the same hornbill species as Sumatra, except that the great hornbill is not found there.In the Neogene (at least in the late Miocene), hornbills inhabited North Africa and South Europe. Their remains have been found in Morocco and Bulgaria. Hornbills are diurnal, generally travelling in pairs or small family groups. Larger flocks sometimes form outside the breeding season. The largest assemblies of hornbills form at some roosting sites, where as many as 2400 individual birds may be found. Hornbills are omnivorous birds, eating fruit, insects and small animals. They cannot swallow food caught at the tip of the beak as their tongues are too short to manipulate it, so they toss it back to the throat with a jerk of the head. While both open country and forest species are omnivorous, species that specialise in feeding on fruit are generally found in forests, while the more carnivorous species are found in open country. Forest-dwelling species of hornbills are considered to be important seed dispersers.