vi BUCEROTIDAE 391 
the unwieldy body acting as a great drag, though counterbalanced 
by the pneumaticity, or air-containing nature of the bones, which 
is perhaps greater in Hornbills than in any other birds. On the 
wing a sound is generally produced like that of a steam-engine, 
Fic. §2.—Hornbill. Dichoceros bicornis. Female and young. (From Malay Archipelago.) 
possibly due to the open nature of the quills; but Rhinoplax, 
Berenicornis, Anorhinus, and Anthracoceros malabaricus are said 
to fly noiselessly. In some species the wing-action is regular ; 
in others, rapid strokes alternate with sailing movements on out- 
spread pinions; the head is usually drawn in and the tail depressed; 
while flocks proceed in single file. Individuals alight heavily, and 
