BRITISH WARBLERS
a vanquished male bears at least the impress of reality—though it must be admitted that the quarrels are often of a transitory nature, mere bickerings, a flying at one another followed by a short pursuit and nothing more; yet even so, the end for which the birds are striving is probably attained. The life of the Wood Warbler affords ample evidence of racial warfare, and the Willow Warbler, probably because it is plentiful and inhabits a similar environment, is of all others the one with which its interests seem more frequently to clash. To observe these quarrels it is necessary to keep in close touch with some particular male from the day of its arrival, to learn its daily routine, and at the same time to know something of the habits of the surrounding species; to interpret them is impossible without the initial knowledge thus acquired. Again and again this mutual antipathy between these two species can be observed during the short period in which they are slaves to the reproductive instinct, and I hope I shall not be accused of needless repetition if I suggest that these struggles ensure, to the stronger, reproduction and a full measure of success in the rearing of offspring, and are therefore related to a larger scheme of which they are but the expression points. It is difficult enough to determine by direct observation whether a species is increasing or diminishing in a particular locality, still more difficult to establish any relation between the success of the one and the failure of the other.
Upon the arrival of a female, a considerable change manifests itself in the behaviour of the male. Previous to her appearance on the scene his daily existence was marked with little excitement apart from the quarrels already referred to, but now that is all changed, the sexual instinct asserts itself, and he becomes for a time the slave of the accompanying emotion. The first indication we have of the near approach of conjugation is one which would scarcely seem to portray an increase of excitement, namely, a decrease in the volume of the song. Instead of exercising his vocal
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