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 disturbance 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 Ravens (Corvus corax) 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 hyperboreus). Waders, e.g., Ruff (Machetes pugnax), and the Black Grouse (Tetrao tetrix). I have not yet had sufficient opportunity 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 lower 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 importance 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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