240 WARFARE BETWEEN DIFFERENT SPECIES 



requires for its functioning a stimulus of an 

 appropriate kind, yet it is also true that the 

 condition which will render it responsive must 

 be present. What we have then to consider is 

 whether the phenomena which we have explored 

 give us any clue as to the particular nature of 

 that condition. In the first place, we have the 

 general fact that the hostility is not confined to 

 a few species belonging to a few families, but 

 that it is of wide application — birds of prey, 

 Warblers, Woodpeckers, all supply us with 

 evidence which serves to show, in greater or 

 less degree, its nature and extent. Next, we 

 found that the hostility was peculiar to a 

 certain season — and that one the season of 

 reproduction. And if the question were asked : 

 What condition would then be most likely to 

 render the instinct susceptible, the answer that 

 would most certainly be given would be — ^the 

 presence of a female. And in reply to a 

 further question as to the particular nature of 

 the stimulus to which the instinct would 

 respond, we should be told — the presence of 

 another male of the same species. Now the 

 possible influence of the female on the course 

 of the male's behaviour was the subject of 

 inquiry in the second chapter, wherein we 

 endeavoured to explain the hostility between 

 males of the same species, and we came to 

 the conclusion that it was not alone sufficient 

 to account for the facts disclosed. Still 

 less likely, therefore, is it that her presence 

 can bear any direct relation to the hostility 



