RELATIONSHIPS IN THE ENVIRONMENT 133 



under similar circumstances, a deterioration so 

 marked that we learn by experience to regard 

 it as a certain indication of the arrival of a 

 mate. 



Thus it becomes clear that there are certain 

 specific factors in the external environment with 

 which the instinct can be definitely related, 

 and in the order of their importance they are 

 (1) the territory as a whole ; (2) the headquarters ; 

 (3) an intruding male ; (4) the female. 



To what extent are these relationships inter- 

 related ? Are they all mutually dependent upon 

 one another, or is there one which conditions the 

 remainder ? 



In the first place it is evident that if a male 

 were not to establish a territory, no opportunity 

 would be afforded for making use of any special 

 post or for acquiring a habit in relation to it, 

 and so without further consideration we may 

 say that the connection between the song and 

 the headquarters, whatever it may be, is 

 primarily dependent upon the establishment of 

 a territory. 



Next, we have the fact that the distant voice, 

 or still more so the presence, of another male 

 has an exciting influence and evokes a corre- 

 sponding reply. Here we have a direct relation- 

 ship, and one which at first sight appears to 

 be exclusive of cross-correlation. But is it really 

 so ; does no circumstance arise under which even 

 the proximity of a rival fails to evoke response ? 

 The reply is not doubtful. Such a circumstance 

 does arise — when a male for one reason or another 



