hornbill

    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, quite like the toucan, 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. In addition, they possess a two-lobed kidney.

       Hornbills are the only birds in which the first two neck vertebrae (the axis and atlas) 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.

Distribution and habitats

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 South Asia to the Philippines and 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 of these species are birds of the more open woodlands and savanna, and some species even occur 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.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 Kalimantan has the same hornbill species as in Sumatra, except the Rangkong Papan (Buceros bicornis).

Description

The brightest colours on most hornbills, like this pair of Knobbed Hornbills, are found on the beaks and bare skin of the face and throat.

Hornbills show considerable variation in size as a family, ranging in size from the Black Dwarf Hornbill (Tockus hartlaubi), at 102 grams (3.6 oz) and 30 cm (1 foot), to the Southern Ground Hornbill (Bucorvus leadbeateri), at up to 6.2 kg (13.6 lbs) and 1.2 m (4 feet).

  Males are always bigger than the females, though the extent to which this is true varies dependent upon species. The extent of sexual dimorphism also varies with body parts, for example the difference in body mass between males and females is between 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, and constructing the nest, as well as 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 serve as a resonator for call.In the Helmeted Hornbill the casque is not hollow but is filled with ivory and is used as a battering ram used 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, although typically offset by bright colours on the bill, or patches of bare coloured skin on the face or wattles. Some species exhibitsexual dichromatism; in the Abyssinian Ground-hornbill, for example, pure blue skin on the face and throat denotes an adult female, and red and blue skin denotes an adult male. The calls of hornbills are loud, and vary distinctly between different species.

Hornbills possess binocular vission, 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.

Female Great Hornbill feeding on figs. Fruit forms a large part of the diet of forest hornbills

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 living species of hornbills are considered to be important seed dispersers

In some instances hornbills defend a fixed territory. Territoriality is related to diet; fruit sources are often patchily distributed and require long distance travel in order to find, thus species that specialise in fruit are less territorial.