Hornbills are to be numbered among the curiosities of nature. They are characterised by the disproportionately large beak. In some species this is nearly a foot in length. The beak has on the upper mandible an excrescence which in some species is nearly as large as the bill itself. The nesting habits are not less curious than the structure of hornbills. The eggs are laid in a cavity of a tree. The hen alone sits. When she has entered the hole she and the cock plaster up the orifice until it is only just large enough to allow the insertion of the hornbill's beak. The cock feeds the sitting hen during the whole period of her voluntary incarceration.
Several species of hornbills dwell in the forests at the foot of the Himalayas, but only one species is likely to be found at elevations above 5000 feet. This is the rufous-necked hornbill.
79. Aceros nepalensis. The rufous-necked hornbill. In this species the casque or excrescence on the upper mandible is very slight. It is a large bird 4 feet long, with a tail of 18 inches and a beak of 8½ inches. The hen is wholly black, save for a little white in the wings and tail. In the cock the head, neck, and lower parts are bright reddish brown. The rest of his plumage is black and white. In both sexes the bill is yellow with chestnut grooves. The naked skin round the eye is blue, and that of the throat is scarlet. The call of this species is a deep hoarse croak.