VI 



BUCEROTIDAE 



191 



the unwieldy body acting as a great drag, though counterbalanced 

 by the pneuniaticity, or air-containing nature of the bones, which 

 is perhaps greater in Horul^ills than in any other birds. On the 

 wing a sound is generally produced like that of a steam-engine. 



Fig. S2. Hornljill. Dichoceros hicornis. Female and young. {Yrora Malay Archijjelago.) 



possiljly 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 



