138 GUIDE TO THE 
developed bill which sometimes has a casque superadded 
to it, but the latter although bulky is not heavy, because 
beneath the thin outer layer of bone covered with cuticle, 
there is a light bony mesh-work filled with air. Another 
feature of the hornbills is the flat sole of the foot and the 
united toes. Their flight is heavy, and the noise made 
by the wings of a large hornbill in progressing through 
the air resembles the labouring of a steam-engine, and 
can be heard at a great distance, Wallace says, as far as a 
mile off. It is one of the characteristic sounds of the forests 
of the Malayan region where the members of the species 
are numerically abundant. They frequent only the loftiest 
trees, hopping about on the stronger branches in a side- 
wise fashion, gathering the fruit that may be within reach 
of their long bills. It has been said that the Rhinoceros 
Hornbill, one of the birds occasionally represented in this 
divison, cannot long sustain its flight owing to the weight 
of its body, and that it has to rest about every mile, but 
the species Rhytidoceros subrujicollis , also a very large bird, 
may be frequently seen in the Mergui Archipelago, flying 
from island to island, and across bays five or more miles in 
width from headland to headland. 
The hornbill has the curious habit, at the breeding 
season, of building the female into the hollow of a tree 
wherein she makes a nest of her own feathers, deposits 
her eggs, and hatches her young. The male plasters up 
the opening with mud, leaving only sufficient space for 
him to insert his bill and feed the female and nestlings. 
It would appear that in order to feed the imprisoned 
birds, the male throws up from his stomach into his bill 
pellets of food enclosed in envelopes or ‘ gizzard sacs/ as 
Dr, Murie calls them, and which he says, “ proved to be 
