228 WARFARE BETWEEN DIFFERENT SPECIES 



When, for example, a Kestrel approaches its 

 territory, it leaves the tree, bush, or rock upon 

 which it was resting, utters its characteristic 

 cry, and soars rapidly upwards ; then, rising to 

 a considerable height, it swoops down upon the 

 Kestrel, and by alternately stooping at and 

 chasing its opponent, drives it away from the 

 immediate neighbourhood. 



What we have, then, to consider is. Do these 

 battles between different species contribute 

 towards the attainment of the end for which 

 the whole territorial system has been evolved? 



Let us take the individual and see whether 

 we can establish any relation between the 

 hostility it displays towards members of other 

 species and its general disposition to secure 

 a territory. We must remember that a male 

 can have no knowledge of the prospective 

 value of its behaviour, nor is it likely that it 

 has any ulterior purpose in ejecting other males, 

 beyond the pleasure it derives from satisfying 

 its impulse to do so. The proximate end of 

 its behaviour is to attack, nothing more, and 

 this, of course, it can only do just in so far 

 as the intruder evokes the appropriate instinct. 



Now the arguments we shall employ will, 

 on the whole, be similar to those which we 

 made use of in the second chapter, wherein 

 we attempted to ascertain the conditions under 

 which a male becomes intolerant of other 

 males of its own species, and examined more 

 especially the claims of the "territory" as 

 opposed to those of the "female." But here 



