BRITISH WARBLERS
is spread over some considerable time; males continue to arrive up to the latter end of May and perhaps even later than this, but it is impossible to say whether all such males are true arrivals or simply individuals that so far have failed to secure a territory. It is evident that in the case of all the more common migratory species, certain individuals will be compelled to wander about in search of territories, and their difficulties in finding them will be great or small according to the environment which they are accustomed to inhabit. The Garden Warbler can no more escape these difficulties than other members of the genus. And so when we think we observe fresh arrivals appropriating territories in the latter part of May we may well be mistaken; what we really observe being nothing but a process of re-arrangement brought about by some change in the available territories of the district. A new breeding ground is often supplied by the clearing away of young trees or the felling of timber in some wood, and the first to take advantage of it will probably be the young males of the surrounding districts, thereby temporarily reducing the severity of the struggle in the immediate neighbourhood. Such re-arrangements I have observed taking place; on the one hand the gradual appropriation of every available space of ground, and, on the other, the gradual desertion of territories as they became unsuited to the requirements of the birds.
The localities inhabited by the bird are similar to those in which we are accustomed to find the Blackcap common. Large or small woods, coppices, osier beds, wooded banks, gardens, or even the outskirts of the forest, afford the necessary shelter; and it would be difficult to point to any one particular type of woodland for which a partiality is shown. The relative number of individuals which visit any one particular locality year by year is subject to some variation; in one season the birds may be plentiful everywhere, in another only moderately so, whilst in a third scarce, a peculiarity which is shared with other migrants. Of the
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