BRITISH WARBLERS
about the same time, Professor Goeldi that they reach Switzerland from the middle of April to the middle of May, Count Salvadori that they arrive in Northern Italy during the latter half of April and the beginning of May, and M. Buturlin that Poland is reached towards the end of April. Southern Russia from the middle of April to the middle of May, the Baltic Provinces during the first half of May. Central Russia about the middle of May, and the Province of Kasan towards the end of that month. Here, then, we have a peculiarly contradictory set of facts. Let us see what the variation amounts to. In England, the normal period of arrival is the end of May, or the commencement of June, in Texel the early part of June, but in Germany and Hungary the beginning of May, one month earlier, that is to say, than the normal period in Western Europe; whilst in Switzerland it is the middle of April and in the South of France the commencement of that month, almost two months earlier than the average date of arrival in this country. Assuming that all these dates are approximately correct, we have a variation which is probably unsurpassed by any other migrant—at least it is not approached by those with which I am more especially familiar. Variation in the case of all migratory species must and does occur up to a point. The more southern parts of Europe are, as a rule, the first to witness the return of these heralds of spring, and even the territories in the southern counties of England are, on the average, appropriated somewhat earlier than those in the north. But in all such cases the difference in time may be more conveniently reckoned in days than in weeks, still less in months. As an example, we have the Reed Warbler which arrives in Hungary about April 20th, ten days or so before it may be expected in England, and the Reed Warbler, be it remembered, is closely related to the Marsh Warbler, a fact which makes the variation in the case of the latter species even more significant. There is nothing to account for this extreme variation; there is nothing, so far as we can judge, in the reproductive instincts of the
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