BRITISH WARBLERS
and in fact appears to be a favourite material. If the branches of the honeysuckle are examined, it will be noticed that the bark of itself peels off and splits up into long soft strands. The female consequently has little difficulty in tearing off the smaller shreds, with which she forms the foundation of the nest; and so much does it resemble decayed grasses that it is often a difficult matter to distinguish it. Honeysuckle abounds in many places resorted to by the Willow Warbler, and its bark is easily collected. It formed the foundation of all three nests constructed by the first female in No. 2 territory, and also of those in the adjoining territories. In fact it is constantly used both by this species and the Chiff-chaff. What particular merit can there be in its use? Why should it be preferred to dead grass? The use of it cannot be of "selection" value, for bark is not obtained more easily than decayed grass; the weaving of it into the foundation of the nest cannot make for stability, and an individual that persistently ignored the use of it would be in no worse a position, since other material in abundance is always close at hand. No doubt an earlier generation would have regarded the habit as an intelligent modification transmitted from parent to offspring, but such a view cannot now be entertained, and the behaviour of the birds does not admit of an appeal to tradition. It is just one of those details which so readily escape our attention on account of their triviality. We ask ourselves how comes it that this material should be used by different individuals and so frequently, call to our aid known laws and theories which in other directions successfully explain certain facts, apply them one by one, and finally lay them aside as unsound or insufficient, humiliated by the vastness of that which we deemed unimportant. The interior part of the nest is formed of the decayed stems of finer grass, intermingled with moss and dead leaves, the lining being usually feathers, but the third nest of the first female in No. 2 territory contained no feathers. All the nests that have come under my notice were situated on the ground, and, where possible, a sloping bank seems to be pre-
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