Description
The Great Hornbill is a large bird, 95–130 cm (37–51 in) long, with a 152 cm (60 in) wingspan and a weight of 2.15–4 kg (4.7-8.8 lbs). It is the heaviest, but not the longest, Asian hornbill. The most prominent feature of the hornbill is the bright yellow and black casque on top of its massive bill. The casque appears U-shaped when viewed from the front and the top is concave with two ridges along the sides that form points in the front, a reference to which is made in the Latin species epithet bicornis. The casque is hollow and serves no known purpose although they are believed to be the result of sexual selection. Male hornbills have been known to indulge in aerial casque butting, with birds striking each other in flight. Females are smaller than males and have bluish-white instead of red eyes although the orbital skin is pinkish. Like other hornbills, they have prominent "eyelashes". The back of the casque is reddish in females while the underside of the front and back of the casque is black in males. The male spreads the preen gland secretion which is yellow onto the primaries and bill to give them the bright yellow colour. The commissure of the beak is black and has a serrated and worn edge with age. The wing beats are heavy and the sound produced by birds in flight can be heard from a distance. The sound produced has been likened to the puffing of a steam locomotive starting up. The flight involves stiff flaps followed by glides with the fingers splayed and upcurled. They are sometimes known to fly at great height over forests.
The species was formerly broken into subspecies cavatus from the Western Ghats, nominate form from the sub-Himalayan forests is sometimes named as subspecies homrai. The subspecies from Sumatra has sometimes been considered as cristatus. The variation across populations is mainly in size, with Himalayan birds being larger than the those from further south and the species is now usually considered monotypic.
Like other members of the hornbill family, they have highly pneumatized bones, with hollow air cavities extending to the tips of their wing bones. This anatomical feature was noted by Richard Owen who dissected a specimen at the Zoological Society of London that died in 1833.
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