Page:The British Warblers A History with Problems of Their Lives - 6 of 9.djvu/19

 to say that the same male and female never meet—since according to the law of chance a reunion must in some instances take place—but to lay it down as a rule that the same individuals meet again and again in consecutive seasons and are consequently paired for life is a different matter, for there could be no rule of that kind unless some useful purpose were thereby served. Inasmuch, however, as the fact that the sexes arrive at the breeding area separately admits of no dispute, and since there is every reason to believe that a similar condition accompanies their departure to the feeding area, it is evident that they are united for part of the year only, and whatever reunion does occur in the breeding season must be in the nature of a casual meeting, having, as we have already seen, little to recommend it as a conditio sine qua non to the pairing of the stronger individuals. In almost every part of these Islands and probably in almost every part of civilised Europe the breeding stations of most of the migratory species are constantly changing. The timber is felled and the undergrowth cleared in some wood, and the following spring it possesses no attractions for the smaller migrants, since the new growth is insufficient to provide them with shelter. But as the seasons pass by and the growth increases, more and more individuals of various species take up their territories until the whole wood becomes an important breeding station resonant with the song of many migrants. Slowly the bushes entwined with bramble and honeysuckle, which used to afford shelter for innumerable nests, increase in stature, pass into saplings, and ultimately check the growth of vegetation beneath, and correspondingly the number of migrants resorting thereto for the purpose of reproduction decreases, until the wood reverts, so far as they are concerned, to its previous state of destitution. Somehow and somewhere these former inhabitants must obtain territories. Urged by their sexual instinct they will wander from place to place seeking a new home, and find, perchance, a resting place in the same locality or possibly suffer banishment from the immediate