REED WARBLER
spring are almost invariably males. I have met with one instance only in this district of a female arriving before a male. In reference to this. Gätke writes in his "Birds of Heligoland" as follows: "In the spring in the case of all species the most handsome old birds are invariably the first to hasten back to the old homes as the heralds of reawakening life; these are soon followed by the old females, whose numbers increase, while those of the males decline, and the migration is brought to a close by the younger birds." It must not be understood from this that the migration of the males is completed before that of the female commences, but that the migration of the sexes overlaps, males continuing to arrive with females. It is important that this should be clear, because there seems to be an impression that the times of migration of the sexes are distinct, that the males arrive, and that after a pause the females follow. For instance, the late Professor Newton, referring to this peculiarity, says: "It has been ascertained by repeated observation that in the spring movement of most species of the Northern Hemisphere the cock birds are always in the van of the advancing army, and that they appear some days, or perhaps weeks, before the hens." And he then proceeds to give this explanation: "It is not difficult to imagine that, in the course of a journey prolonged through some 50° or 60° of latitude the stronger individuals should outstrip the weaker by a very perceptible distance, and it can hardly be doubted that in most species the males are stouter, as they are bigger, than the females." Had he known that the migration of the sexes overlaps, that a few males arrive, forerunners of the advancing army, but that afterwards males and females arrive intermingled, it is probable that his interpretation would have been modified. And even if it be granted that the males are the stronger, this cannot account for their outstripping the females by a week, ten days, or still less by a fortnight in a journey of perhaps 1,500 miles. To expect them to accomplish such a distance in from four to five days is surely not estimating their
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