Page:The British Warblers A History with Problems of Their Lives - 5 of 9.djvu/19

 growth of the reeds from year to year in the second week of May in this country is slight, and does not appear to me to be sufficient to influence their movements. Moreover, it is not possible for a species in a foreign land to be cognisant of the state of growth of the reeds in these islands. If it can be shown that there is any relation between the two, an explanation must be sought in some peculiar climatic conditions which, while delaying the departure of the migrants, would at the same time retard the growth of the reeds. In Hungary I found these birds plentiful in the year 1905 on April 26th, and there is little doubt that they had already been there some time. On the other hand. I have no records of their arrival in this county earlier than May 1st. In the year referred to, the growth of the reeds in Hungary was undoubtedly in advance of the growth in this country. So that before we attempt to understand this question of migration, we must be in a position to decide whether, on the average, the same individuals migrate to the same country year after year. There are some grounds for believing that they do so, for it is clear that those individuals that reach Hungary about April 20th must have commenced their journey some time before those that reach this country during the first week in May.

Both males and females arrive throughout May and part of June, even as late as the 21st of the latter month. But it is by no means unlikely that some of the individuals are not "arrivals" in the sense of having only completed their journey that particular day. Indeed, it is impossible to distinguish between a male moving from pool to pool seeking territory, or similarly a female in search of a male, and a true arrival, that is to say, a bird that has only comparatively recently commenced to travel from its winter home. These later arrivals may not, therefore, be migrants in the narrower use of the term, but only individuals unsuccessful so far as reproduction is concerned. Yet it is well-nigh impossible to decide this by actual observation. Their plumage has no