BRITISH WARBLERS
circumstances, and this shyness continues throughout the whole period of reproduction. If I cut away the undergrowth and make a clear opening so as to be able to observe them at the nest. I find that they have difficulty in overcoming their natural timidity. Only when one stands some distance away can they be persuaded to approach the nest, and this distance requires to be much greater than is necessary in the case of the Reed Warbler. During incubation it is impossible to be too careful in taking up one's position, and even when a post from which observations can be taken has been successfully reached, it is essential that little or no movement should be made if suspicion is not to be aroused. I am inclined to doubt whether the birds really become reconciled to the human presence after the young are hatched, for it will be noticed that they then carry out their duties hurriedly, over anxious apparently to finish the task they have in hand. One of the sexes is more timid than the other, though it is difficult to determine which, but since in the case of the Reed Warbler it is the male that is the more nervous, it is probably the male that lacks courage in this species; all this timidity tends to show that the temperament of the bird is different from that of the Reed Warbler, and it is interesting to note that the greater timidity seems to be correlated with a greater nervous development in other directions. It may here be mentioned that the male, when approaching the nest in order to relieve his mate, sometimes utters a few phrases of his song, and also that the presence of a Red-backed Shrike (Lanius collurio) near the nest seems to cause him much anxiety, which he shows by moving restlessly to and fro and vigorously uttering his scolding note so long as it remains in the vicinity.
There is considerable variation in the length of time that the young of different pairs remain in the nest. Development appears to be more rapid in one case than in another. One nest will be deserted at the end of ten days, whereas another will still be a nursery at the end of fourteen. Ten days is
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