Hornbill - Description

Description

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 it to serve as a resonator for calls. 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 exhibit sexual 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 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.