BRITISH WARBLERS
namely, why, in the case of two such closely allied forms living in a similar environment, one should arrive at its breeding ground so much in advance of the other.
The law of breeding territory forms as important a part in the life-history of this bird, at this particular season, as it does in that of so many others. Similar conflicts occur, similar petty struggles; in fact, the whole routine of the life of the male, previous to and after the arrival of the female, may be said to be almost identical with that of the male Chiff-chaff. Inasmuch, however, as this law seems to be one of some importance in the life of many species of birds, and possibly other vertebrates, I shall describe minutely any details that have come under my notice bearing upon the question, no matter how small or perhaps even trivial they may seem, and no matter how similar to those in the life of the Chiff-chaff or any other species already dealt with. In order to observe the behaviour of the birds during this period, it is as well to select some wooded bank inhabited by a number of males and divided into a number of adjoining territories. For such territories are never very large—although they vary considerably in extent, being perhaps twenty-five, forty, or sixty yards in length—and consequently it is by no means impossible to keep three adjoining areas under observation at the same time, which is an advantage and often an assistance in enabling one to interpret the actions of the different inhabitants. Moreover, where possible, the same wooded bank or plantation should be selected for two or three years in succession, since by this means alone is it possible to discover through actual observation whether the same males return to the same territories year after year; and besides, by so doing, one commences each season with a considerable and important knowledge of the previous life-history of the various inhabitants of that particular locality. As to whether the same males do return to the same territories we know very little. There are certain authenticated facts which show that birds do sometimes revisit their birthplace, and, in the case of the
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