PICABJAN BIRDS. 91 



Family X. BUCEROTIDJS. HORNBILLS. (Plate XIX.) 



These remarkable looking birds, ranging from Africa and the Indo- [Cases 

 Malayan regions to the Solomon Islands, derive their name from their ' '" 

 immensely developed bill, surmounted in most of the genera by a 

 variously-shaped casque, which is often of large dimensions and gives 

 them a singularly top-heavy appearance. In spite of their size, the bill 

 and casque are not nearly so weighty as one would suppose, being 

 merely a horny shell supported internally by a cellular bony tissue 

 of extreme delicacy. This structure may be seen in the sections of heads 

 exhibited in the Case, that of Dichoceros bicornis (1 190) [PI. XIX. figs, c 

 & d~] illustrating the normal type; while Bucorax abyssinicus (1188) 

 and Rhinoplax vigil (1212) are peculiar, the former in having the casque 

 open anteriorly, the latter in having the anterior wall solid and the 

 posterior part nearly filled up with parallel bony columns. The bones 

 of the skeleton are also unusually pneumatic. The edges of the 

 mandibles are generally roughly serrated, and the eyelid is furnished 

 witli strong lashes. The feet have broad soles, the second, third, and 

 fourth toes being partially united. Though often prolonged for 

 considerable distances, the flight is heavy, slow, and extremely noisy, 

 the sound, which has been likened to the rushing of an express train, 

 being probably caused by the air passing between the open bases of 

 the quills at each beat of the wings. 



The nesting-habits of these birds are peculiar, and of extreme interest. 

 After the eggs have been laid in the hollow of a tree, the female 

 commences to incubate, arid the male (sometimes assisted by his mate) 

 closes up the entrance to the nest with a very hard clay-like substance, 

 leaving only a small slit through which the female can protrude her bill 

 and receive the fruits he brings her. If the male is killed, other males 

 are said to take his place and provide the female with food. The object 

 in closing in the female is no doubt to protect her from the attacks of 

 monkeys and other enemies. 



The female is said to remain imprisoned until the young are fully 

 fledged, and in some species at least the wings and tail are shed and 

 renewed during this period, the moulting of these feathers being no 

 doubt a welcome relief to the bird in its cramped and stuffy cell. The 

 adjacent table-case, containing the nesting-site of one of the smaller 

 African Hornbills (Lophoceros melanoleucus) (1204) illustrates all these 

 interesting facts. 



The numerous species are divided into two subfamilies, Bucoracinte 

 and Bucerotina ; the former including only two very large African 

 species of Ground-Hornbills characterised by their long legs, which are 

 well-adapted for walking. The Abyssinian Ground-Hornbill (Bucoru.K 



