OO BiCKNELL on the Singing of Birds. [January 



sons, song is not discontinued until tlie niovilt is completed and 

 fat has begun to develop. This species thus illustrates decadence 

 of vocal vigor during activity of the moult, and complete cessation 

 of song with the adipose condition supervening. Other similar 

 evidence could also be adduced. 



But I do not forget that our evidence is fragmentary and uncer- 

 tain. Whether disuse of the vocal organs directly results from 

 the physical condition with which we find it associated, or from 

 some collateral cause, we are ignorant. But it is certainly easy 

 to understand how excessive fatness might result in reduced emo- 

 tional sensibility or indisposition to vocal effort, or how a devel- 

 opment of adipose tissue about the vocal organs might interfere 

 with their free action. Bird-fanciers recognize the injurious 

 effect of over-feeding on the vocal power of cage birds. 



Song, as an immediate result, appears to be the outcome of 

 emotion or excitement, and reaches its highest expression, with 

 its highest use. during the mental and physical excitement of the 

 breeding season. Ever}' one who has been an observer of birds 

 must believe them to possess high cerebral sensibility. The in- 

 fluence of almost impalpable meteorological changes on the sing- 

 ing of birds cannot fail to have been remarked, and the eftect of 

 tlecided weather changes must often have been apparent even to 

 the most unobservant. While with many species the habit of 

 supplementary song, if I may so term the habit of singing in the 

 autumn, is firmly established, with others it is inconstant and 

 greatly dependent on favorable conditions of weather. The sup- 

 plementary song-period is thus often of uncertain duration, and it 

 even happens with certain species that it is confined to a few days, 

 or, as it sometimes appears, even to one. 



Instances of the effect of mental excitement on the singing of 

 birds are constants before us.. Birds suddenly disturbed or start- 

 led from their letreats, or abruptly ceasing from a headlong chase 

 after or flight from a companion, often break forth with sudden 

 song, sometimes even at a time when the species is ordinarily 

 silent. So, too, the excited repetition of an alarm note not infre- 

 quently leads up to a sudden burst of song. 



This brings us to the consideration of a habit possessed by some 

 of our birds of singing while on the wing. With some species 

 singing during flight is but an ordinary occurrence, as in the case 

 of the Bobolink, which continually overflows with melody during 



