134 RELATION OF SONG TO THE TERRITORY 



passes outside the limits of its accustomed area. 



This aspect of behaviour has aheady been fully 



discussed in connection with the question of 



hostility, and everyone, I imagine, must by 



now be pretty well _ familiar with the facts. 



However, it does not often happen that we 



are given such an aid to interpretation as is 



vouchsafed to us in the altered behaviour of 



the male when it joins the flock, and if, as 



I believe, song and hostility are intimately 



associated, forming part of an inter-related 



whole which, for biological interpretation, has, 



as its end, the attainment of reproduction, it 



is not surprising that circumstances which lead 



to the modification of the one should likewise 



affect the other ; I offer no apology, therefore, 



for adverting to this aspect of behaviour once 



again. 



Now a male may leave its territory for three 

 reasons — to pursue an intruder, to join the flock 

 on neutral ground, or to find the necessary means 

 of subsistence on other feeding grounds. On 

 each of these occasions it hears the song of, and 

 is in close contact with, other males ; and if the 

 relationship of which we are speaking be really 

 exclusive of cross-correlation, its instinct ought 

 to respond with the customary freedom. But 

 what happens ? A male pursues its rival, 

 betraying much emotion and singing extrava- 

 gantly, until the boundary is passed, when 

 emotion subsides and it is silent ; or, it flies to 

 the flock on neutral ground, and, although 

 surrounded by the very males that a short time 



