176 Bird Comrades 



sounds, are generated they are simply piped or fluted 

 through a slit, so that birds are whistlers, not singers 

 or vocalists. I repeat, so that my meaning may be per- 

 fectly clear bird music is not produced by means of 

 vocal cords, as is the music of the human throat, but by 

 means of a whistling aperture in the larynx. And that 

 wonderful cleft has been placed there for that specific pur- 

 pose. Properly speaking, therefore, the feathered choralist 

 does not have a voice, but only a wind instrument; 

 albeit a marvelous contrivance it is. 



It will be easy now to see how the bird's tones are 

 capable of a large variety of modulations. The glottis is 

 controlled by a system of muscles that are perfectly obe- 

 dient, within their limits, to the bird's volitions, and thus 

 it may be made to assume a great number of different 

 forms, each giving expression to a different vocal effect. 

 The shape of the glottis is also modified in numerous ways 

 by the movement of the tongue and mandibles. Nor is 

 that all, for the air column pumped up from the lungs 

 may be increased or diminished at will, a very strong 

 current producing a loud tone, and a feeble current a low 

 one. The elongation or contraction of the whole throat 

 will also modify the pneumatic column, and thereby alter 

 the quality of the tones. 



We may go still further in our analysis. Suppose a 

 bird should open his mouth and throat as widely as possi- 

 ble, hold all his lyrical organs steady, and blow his wind- 

 pipe with all the strength his lungs could command, it is 

 obvious that the effect would be a clear, loud, uniform 



