RELATIONSHIPS IN THE ENVIRONMENT 131 



occasion. The question therefore arises as to 

 whether the emotional outburst which we are 

 attributing to the arrival of a female may not 

 after all be due to the presence of an intruding 

 male. It may be so. But although I can recall 

 no single instance in which the presence of an 

 intruder could be definitely excluded, yet I 

 should hesitate to base upon this any broad 

 generalisation. 



When the normal course of the song is not 

 interrupted by the arrival of a female, when, 

 that is to say, the male still pursues the routine 

 to which he has all along been accustomed, 

 and still sings at stated intervals in stated 

 places with a voice that betrays no heightened 

 emotional tone, even though the song may 

 convey some meaning to the delicate perceptual 

 powers of the female, we have nothing to lay 

 hold upon which can be construed as an indica- 

 tion of direct relationship between the song 

 and the presence of the female. 



The partial or complete suspension of the 

 song after pairing has taken place is the most 

 interesting, as it is the most noticeable, feature. 

 Not that it is by any means universal — if it 

 were so, some of the difficulties that beset the 

 path of interpretation would be removed, but 

 it is sufficiently widespread to demand explana- 

 tion. In nearly every case it is, however, 

 only temporary, the period during which the 

 male is silent varying from a few days to a 

 few weeks. The male Grasshopper- Warbler, 

 when it first reaches us, sings persistently, but 



K 



