BRITISH WARBLERS
the fact of the bird flying from place to place, and even making initial attempts at construction, we seem to be presented with evidence of conscious deliberation. Hence some may affirm that she carries in her imagination a mental image of the nest she is about to construct, and thus decides in advance as to the relative merits of the various situations. But a young bird is capable of constructing a nest antecedent to experience, and manifestly has no mental image before it, and cannot well make use therefore of any such complicated process of reasoning. Is it then necessary to demand such a power for the adults?
The nest is placed in various situations—in perpendicular osiers, amongst common nettles (Urtica dioica), cow parsnip (Heracleum sphondylium), meadow-sweet (Spiræa ulmaria), wormwood (Artemisia absinthium), dogwood (Cornus sanguinea), tall grass, and not infrequently in young ash plants. In giving the results of his long experience with these birds in Oxfordshire. Mr. Warde Fowler writes as follows: [1][2]"But here I may remark that it is not every kind of osier willow that suits our bird; I have never found the nest in any but the Salix triandra, which sends up pliant perpendicular shoots quite close to each other. The other osier to be found in all withy beds (S. viminalis) is in every way less suitable. If the osiers in the favourite breeding place have been cut, and the season is late, the birds will be in serious difficulties, and will search for suitable sites in hedges and ditches, and have recourse to nettles, wild parsnip, or even beans, as we have seen. Here, of course, they run far greater risks than in the dense vegetation of the osier-bed, where I have hardly ever known a nest destroyed or even discovered by the ploughboys who are constantly about the spot. The difficulties met with by my birds during the last few years lead me strongly to believe, apart from other evidence, that the Marsh Warbler is not, and cannot be, a more abundant bird than we
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