Page:The British Warblers A History with Problems of Their Lives - 6 of 9.djvu/15

 description, and therefore the prefix "Willow" which has been applied to it, and which may seem somewhat trivial, is in reality expressive of a characteristic, though but a small one, of the species.

In the order of migration the bird must be placed between the Chiff-chaff and Wood Warbler, since it arrives considerably later than the former species and somewhat earlier than the latter. As in the case of the Chiff-chaff, the date of arrival varies year by year—at least in the west Midlands where my records have been kept—the earliest record I have being March 30th, and the latest April 16th. On the average the first males may be expected towards the latter end of the first week in April, but all the males do not arrive on the same day or during the same week, the migration extending over some days. Neither do they all arrive before the females, but the majority do so; the first females, however, are usually later by a week or more in reaching the breeding grounds than the first males. Meteorological conditions no doubt influence the migration and are a cause of erratic movement. Insect life is scarce in cold springs, and in exceptional weather almost entirely absent for a time, and upon insects these birds entirely depend for sustenance at this season of the year. When, therefore, we find the smaller and more delicate-looking Chiff-chaff a fortnight earlier still at this critical period, we naturally seek an explanation. What difference there can be in the constitution of the Chiff-chaff that enables it to face such inhospitable conditions so much earlier we do not know, and yet there must be some reason, some advantage to be gained by its doing so. Can it be that the restless activity, so prominent a feature of its behaviour, enables it to find a living even under the most adverse conditions? It may be so, for in studying the two species the Willow Warbler certainly appears to be less active and rather more sluggish in its movements. But although this may be a reasonable explanation of the one being able to exist under more trying conditions than the other, yet it leaves the main difficulty unsolved,