THE LOVE DISPLAYS OF BIRDS 217 



perceptibly in brilliancy and persistency after 

 the laying period is over, and the more acute 

 stages of sexual strife are passed. That won- 

 drous, if soberly arrayed, songster the Nightingale 

 loses his sweet music as the young are hatched, 

 and his entrancing voice becomes a disagreeable 

 croak until passion inspires it anew the following 

 season. The singing period of all song-birds is 

 a season of irritation and war. Rival males sing 

 at each other, chase each other from tree to tree, 

 fight fiercely, and sometimes seem so lost in 

 their ecstatic rage as to become oblivious to their 

 own personal safety. Birds have been known 

 actually to die under the violent exertions of 

 song that a rival has inspired. 



The very perceptible amount of individual 

 variation in the song of birds must be men- 

 tioned. This is a very difficult study, for it 

 requires a sensitive musical ear and some train- 

 ing to pursue it ; and yet it forms a most pro- 

 mising and pleasing field of inquiry. Another 

 puzzling question relating to song is the imita- 

 tion of other birds' notes practised by various 

 species. The standard of perfection in song is 

 also by no means a constant or uniform one. 

 We find a considerable range of variation in 

 this as in all other things. This is especially 



