Bucerotidae – Hornbills

The Phoeniculidae or Hornbills are a family of near passerine birds in the Bucerotiformes order, along with Phoeniculidae (Wood Hoopoes & Scimitarbills) and Upupidae (Hoopoes).

Until recently Ground Hornbills were classed as a separate family (Bucorvidae) of the order Bucerotiformes, with a single genus Bucorvus and two extant species (though possibly including another genus with six extant species). That group is endemic to Sub-Saharan Africa. They are large, with adults around a metre tall. Both species are ground-dwelling, unlike other hornbills, and feed on insects, snakes, other birds, amphibians and even tortoises. They are among the longest-lived of all birds and the larger southern species is possibly the slowest-breeding (triennially) and may be the longest-lived of all birds. It is currently thought that the ground hornbills, along with Tockus and Tropicranus, are almost exclusively carnivorous and lack the gular pouch that allows other, less closely related hornbill genera to store fruit. They are now considered to be a different clade of the one family.

Southern Ground-Hornbill Bucorvus leadbetteri – ©Dubi Shapiro

The Bucerotidae or Hornbills are, as a whole, a family of birds found in tropical and subtropical Africa, Asia and Melanesia. They are characterised by a long, down-curved bill which is frequently brightly coloured 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.

Oriental Pied Hornbill Anthracoceros albirostris – ©Dubi Shapiro

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 their large bills. 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.

Southern Yellow-billed Hornbill Tockus leucomelas – ©Dubi Shapiro

Hornbills show considerable variation in size, ranging from the Ground Hornbills and Black Dwarf Hornbill Tockus hartlaubi, at 102 grams and 30cm. 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 as little as 1% to as much as 17%, but the variation is 8% to 30% for bill length and 1% to 21% in wing length.

Von der Decken’s Hornbill Tockus deckeni – ©Dubi Shapiro

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.

Silvery-cheeked Hornbill Bycanistes brevis – ©Dubi Shapiro

Their plumage 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.

Blyth’s (Papuan) Hornbill Rhyticeros plicatus – Dubi Shapiro

The calls of hornbills are loud and vary distinctly between different species. They 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. They 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 have been recorded.