242 WARFARE BETWEEN DIFFERENT SPECIES 



behaviour of the migrant, that lacks the " will 

 to fight " when on migration but is pugnacious 

 when it has secured a territory, shows it ; the 

 behaviour of the resident, which temporarily 

 joins the flock and is there sociable, shows it ; 

 and it is shown also by the determination with 

 which both opponents fight when the question 

 of ownership of a station is in dispute. And of 

 all the facts we have reviewed, this is perhaps 

 the most important in relation to our present 

 subject, for it demonstrates that the change 

 from sociability to hostility is not merely an 

 incident of the sexual season, not merely an 

 indirect result of the functioning of the general 

 disposition which leads to the establishment of a 

 territory, but that it is intimately associated 

 with the whole process, and that the particular 

 part of the bird's nature which is concerned is so 

 nicely balanced that it will respond under one 

 condition and one only. 



Thus we are led to the only conclusion 

 which seems consistent with the facts, namely 

 that there is a relationship between the 

 "territory" and the hostility. 



If we are satisfied that all this warfare is not 

 merely an expression of an instinct which is 

 serviceable in another direction, what part does 

 it play in the whole scheme of reproduction ? 



The young of many birds are delicate at 

 birth and unable to withstand exposure to cold, 

 and in the previous chapter we came to the con- 

 clusion that the territory was serviceable in that 



