BRITISH WARBLERS 



that she is sometimes attacked by the owner of that territory. 

 But if she is followed by the male with whom she has paired, 

 it almost always leads to a struggle. Considerable dis- 

 turbance may also be caused by two pairs whose territories 

 adjoin attacking one another. It is difficult to say with 

 any degree of certainty what is the cause of such battles, 

 though it sometimes seems to me possible to trace the origin 

 to some female, recently arrived, not confining herself to 

 the boundaries of the territory in which she has settled. 

 But whatever it may be, the conflicts, when they do occur, 

 are very fierce, the males and females attacking one another 

 respectively. That Peregrine Falcons (Falco peregrinus) and 

 Eavens (Corvus cor ax) will not allow another pair to breed 

 in proximity to them is well known; and from the accounts 

 of other observers the same law appears to be in operation 

 in the case of the Bed-necked Phalarope (Phalaropus hyper- 

 boreus), Waders, e.g., Puff (Machetes pugnax), and the Black 

 Grouse (Tetrao tetrix). I have not yet had sufficient oppor- 

 tunity of studying the cliff-breeding sea birds to enable me 

 to bring forward any direct evidence from their lives, but 

 from what I have seen little doubt remains in my mind. 

 that " acquisition of breeding territory " has exercised and 

 is exercising a considerable influence on their life-history. 

 How far this law extends it is impossible to say ; the evidence 

 is sufficient to show that it holds good with many species, 

 and I shall not be surprised to learn that it is a vera causa 

 of the battles so common between the males of many species 

 of mammals and low T er vertebrates. 



In the life-history of the Whitethroat I have described 

 a struggle between the females, and the attitude of the male 

 in whose territory the battle was taking place, and I then 

 suggested that the struggle seemed to be one of some import- 

 ance to this theory. The females of some species are more 

 brightly coloured than the males, and in such cases it is they, 

 and not the males, that are pugnacious and fight with one 

 another. This is so with the Phalaropes. The female Moor- 



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