MARSH WARBLERS
fluff out the feathers both on her breast and flanks. All these antics are the special accompaniments of the sexual instinct, and we can well imagine that it would be during this short period—that is to say, previous to the actual discharge of the sexual function—that the instinct would reach its maximum development. Nor is it unreasonable to suppose that after each discharge there should be a lessening in the intensity of the instinct accompanied by a decrease of the motor reactions; observation at least seems to show that this really is the case.
Whether the female first selects a position for her nest and then goes in search of material is difficult to determine, but judging by her behaviour this does not appear to be her method of procedure. For this is what occurs: she tears off dead material of some kind, and flies from place to place holding it in her bill. Making her way into some thicket, she reappears, having left therein the material she was carrying. For a time she is then lost to view, but presently comes again into sight in the same vicinity carrying a further supply of dead grass. This time, however, she wanders about in uncertainty, and finally deposits it in an entirely different situation, albeit only a few yards away. This spirit of uncertainty ultimately deserts her; a position is found suitable to her requirements, and forthwith she sets about her task in earnest, going repeatedly in search of material, and upon returning therewith fixing it rapidly; thus the nest gradually begins to assume some shape. Regarding the psychology of the bird's behaviour it is perhaps wise to say but little. Is the whole situation a conscious one, and, if so, how far conscious? Does the bird, that is to say, reflect upon the possibilities of this position or of that, ultimately come to a decision, and forthwith commence to build? Or is the mental process an altogether more simple affair, congenital rather than individual, having its origin in some internal impulse called forth by the sight of the requisite situation? Personally I am inclined to the latter view. It is true that in
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