STRUCTURE OF BIRDS 



hornbill manages to balance on its head, with a 

 deceptive appearance of great weight, is somewhat 

 of a problem to naturalists, though we have seen 

 it suggested that it may serve as a resonator to 

 increase the power of the voice, the characteristic 

 note of these birds being between the bray of an 

 ass and the shriek of an engine whistle. How far 

 the form of the bill affects the voice is an interest- 

 ing question ; and it is stated that some birds, the 

 cuckoo for example, will sing without opening 

 the beak at all. 



In other cases sounds are made by the beak 

 alone, notably in the stork, which clatters its two 

 mandibles together like a pair of castanets. 



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