214 Habit and Instinct. 



this is heard for the roost part in the pairing season 

 indicates its association with the mating instinct and 

 the emotional condition appropriate to the season of 

 courtship. In this season life is at high tide; there is 

 an unusual expenditure of energy; and some of this 

 energy finds vent in the joyous stream of song. If this 

 be not an expression of emotion, we must give up all 

 attempts at subjective — or, as Clifford termed it, ejective — 

 interpretation of observable activities. But if, as we have 

 been led to infer, expression is for external reference, and 

 has suggestive value, the conclusion is irresistible that 

 the male bird sings for his mate, and that the biological 

 value of song is to call forth an answering emotion on his 

 part. 



We here open up the question of sexual selection, 

 which is associated with the revered name of Charles 

 Darwin; and it may be well to state his views on this 

 subject in his own words. " Most male birds," he says 

 in his summary,* " are highly pugnacious during the 

 breeding season, and some possess weapons adapted for 

 fighting with their rivals. But the most pugnacious and 

 the best-armed males rarely or never depend for success 

 solely on their power to drive away or kill their rivals, 

 but have special means for charming the female. With 

 some it is the power of song or of giving forth strange 

 cries, or instrumental music, and the males in conse- 

 quence differ from the females in their vocal organs, or in 

 the structure of certain feathers. From the curiously 

 diversified means for producing various sounds, we gain a 

 high idea of the importance of this means of courtship. 

 Many birds endeavour to charm the females by love-dances 

 or antics, performed on the ground or in the air, and 



* " Descent of Man," vol. ii. part ii. chap. xvi. pp. 250-256. 2Qd 

 edit., 1888. 



