Hornbills 501 



largely greenish. They are forest-haunting birds, usually seen solitary or in 

 pairs, perching on the higher trees and feeding on insects, which they capture 

 on the wing. Their nesting habits so far as known are similar to those of Bee- 

 eaters in general. 



THE HORNBILLS 



(Family Bucerotida) 



It is hardly necessary to state that the Hornbills comprise a very remark- 

 able and strongly marked group of birds, the members of which are not likely 

 to be confounded by even the casual observer with any other group, unless 

 perhaps the Toucans; but as the latter are exclusively Mexican to South American, 

 while the Hornbills are confined to the Old World, the possibility of such con- 

 fusion is reduced to a minimum. Curiously enough these great birds, with 

 such grotesquely enormous bills, appear to find their closest relationship with 

 the graceful little Hoopoes; so closely, in fact, are they related that Gadow 

 would only accord them subfamily rank under the Upupidce; but the differences 

 in structure, appearance, and life habits are so very marked that they seem 

 entitled at least to full family rank, and many systematists have placed them 

 still higher. Their resemblance to the Toucans is brought about by the some- 

 what similarly appearing large bills, but this likeness is quite superficial, and 

 there is really no close relationship between them. 



Structure. The Hornbills are mostly birds of large size, several exceeding 

 four feet in length, and few falling under two feet. They are chiefly remark- 

 able for the large, often very large, bill which is surmounted in many species 

 by a casque, which may itself be so large as to appear like a second bill above 

 the other, while in other forms it is quite rudimentary or even reduced to a mere 

 keel. The bill and casque, in all but one of the Hornbills, is hollow with quite 

 thin walls and supported inside by a cancellated bony structure. In the Solid- 

 casqued Hornbill (Rhinoplax), as the name implies, the whole of the anterior 

 wall is solid. In a majority of forms the casque is closed, the exception being 

 in the Ground Hornbills (Bucorax), in which it is more or less open in front, 

 giving them a very peculiar appearance. Structurally the Hornbills have the 

 palate of the bridged (desmognathous) type, no basipterygoid processes or caeca, 

 while the breast-bone is broad behind and provided with two notches as in the 

 Hoopoes; the whole skeleton is unusually pneumatic. Among other more or 

 less important characters it may be mentioned that they have well-developed 

 eyelashes, a feature not common among birds, usually large, powerful wings, 

 and a tail of ten feathers, the central pair of feathers being in some cases much 

 longer than the others. The wings are further peculiar in that the under coverts 

 do not cover the basal parts of the quills, and it has been suggested that it is 

 the air rushing between the bases of the quills that produces the loud sound 

 heard when they are in flight, a noise that has been likened to a railway train 

 at a little distance. 



