Some Naturalists divide the Passerines into five great groups, the first based upon the structure of the feet, the other four on the formation of the bill. Others object to this classification because it is not always possible to assign a place to certain groups because of peculiarities of their beak alone. This distribution is generally followed, however, as it is easy to remember.
As the different members of the great Passerine or Sparrow family are nearly all Perching Birds, it is easier to give them this classification in dividing them into groups, and thus avoid the many Latin names that it is not necessary to remember. In the first group we find the Perching Birds with united toes—the outer toe being nearly as long as the middle one and fast to it. This group includes the Hornbills, the Fly-catchers, the King-fishers, the Bee-eaters, and the Motmots.
The Hornbills are remarkable for their enormous development of beak, which is long, very wide, compressed, and more or less curved and notched, and in some species surmounted by a large helmet-like protuberance. This immense beak is nevertheless very light, being spongy, as in the Toucans. The Hornbills have in some respects the bearing of the Crow; this led Bontius to class them among the Crows, under the name of Indian Crow. They walk with difficulty, and their flight is clumsy, their favorite position being on a perch at the summit of lofty trees. Great flocks of these haunt the forests of the warmer regions of the Old World, especially Africa, India, and the Oceanic Archipelago. They build their nests in the hollows of trees. They are omnivorous. The fruits, seeds, and insects of those regions are their principal food; yet they will not refuse flesh.
In India they are domesticated, their services in destroying rats and mice being valuable. The plumage of the Hornbill is black or grey, of various shades; but there is a species described by Dr. Latham and Dr. Shaw under the name of the Crimson Hornbill, which Mr. Swainson thinks may prove to be a link between Toucans and Hornbills, and thus combine the beauty of plumage of the former with the peculiarity of form of the latter. Their flesh is delicate, especially when fed on aromatic seeds. Many species are described, varying in size, among which the Rhinoceros Hornbill is the most worthy of notice. This bird is so named from the singular protuberance with which its bill is surmounted; this is a smooth horny helmet, curving upwards from the bill, somewhat resembling the horn of the rhinoceros. It is a native of India and the islands of the Indian Ocean.