Page:The British Warblers A History with Problems of Their Lives - 5 of 9.djvu/38

 of the strength of the species? And if territory is an essential to reproduction, and the final appeal for territory is to the strength of the individual male through the law of battle, of what use could it be for females to arrive before males? On the other hand, if the first step towards reproduction is to find an unpaired male in possession of a territory, what would be the position of a female that, from one cause or another, was late in arriving at the breeding grounds? The balance between these extremes, that is to say, between a too early and too late arrival, must have been gradually adjusted to suit the needs of different species.

The second observation is that which has reference to the banishment of the young by the parents. It is well known, in the case of many species, that the parents drive away their offspring as soon as they are able to take care of themselves; and the reasons generally given for this behaviour are, firstly that the supply of food would not be sufficient to maintain both old and young, and secondly, that interbreeding would thus be prevented. While it is no doubt true that both these ends will ultimately be attained, yet neither one nor the other can be the motive force which impels the parent birds to act in so arbitrary a manner, for each would imply an amount of forethought of which no bird is capable. Must we then regard the habit as a chance variation, which, having once arisen at some early stage in the history of bird life, was perpetuated, owing to its having been of some direct benefit to those species possessing it? Or is it not possible that it is linked with some other mode of behaviour? The latter appears to me to be the more probable alternative, and it is by no means unlikely that it has its origin in, or rather is an extension of, the law of territory. As in so many cases, an interpretation is rendered the more difficult by the fact that the habit is not a universal one, but seems to be confined to certain species only. The Moorhen treats its young, when they are able to find food for themselves, with scant affection, pursuing and pecking them unmercifully, and the Stonechat will not allow