BRITISH WARBLERS
calls forth unusual energy and effort on the part of an insectivorous species; otherwise it must succumb. And doubtless it is this great activity which enables the Chiff-chaff in the latter part of March to discover sufficient insect life to prevent such an undue lowering of its vitality as might render it less able to withstand the cold inclement weather so common at that season of the year. Nevertheless, if we regard the relative positions of the two species, we must conclude that the greater strength of the Willow Warbler, which enables it with more certainty to secure a breeding territory, is of higher importance than the activity of the Chiff-chaff, since the former bird is more plentiful and more generally distributed than the latter.
There seems to be some connection between the song—or the sounds that answer to song—and the territory. The actual song is in the case of many species so remarkable and beautiful that it at once arrests our attention, and we naturally ask ourselves the meaning of it, whence it originated, or how it developed. To these questions no satisfactory answer has yet been forthcoming. Just why a Blackcap can produce such very beautiful notes and a Grasshopper Warbler such peculiar and monotonous ones is as great a mystery to-day as ever, and I do not pretend to be able to throw any light on the mysterious aspect of it, but only to indicate one direction in which it may be of some use. We must dismiss from our minds all ideas of aesthetic value, for it is clear that if there be any utility attached to the various cries, those which may sound to our ears harsh or even repulsive must, if uttered under similar conditions and at a similar season, be of equal importance to those which delight us with their beauty. The males of the summer migrants reach their destination many days before the females, take possession of their territories, and there remain singing incessantly during the first few hours of daylight, and in a lesser degree throughout the remainder of the day. The males of some of the resident species, the Chaffinch for instance, take possession of their territories very early in the year, and
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