Page:The British Warblers A History with Problems of Their Lives - 5 of 9.djvu/39

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its young to remain in its territory. The instinct is better known, perhaps, in connection with the birds of prey and the Raven; and in some cases it seems to be deferred until the following spring; young Partridges, for example, remain with their parents throughout the winter. Hitherto, I have not been able to trace it amongst the Warblers. Whether it is more prevalent amongst those species that rear two broods, or whether it is limited to those that remain more or less in one particular territory throughout the year, we do not know. A Warbler deserts its territory as soon as the young are reared, but the Moorhen as a rule continues in the same place during the winter months. A migratory species would have nothing to gain by driving away its young, for although it is likely that both old and young return to the same district the following spring, yet it is not probable that the young would lay claim, even if the parents did so, to the identical territory in which they were reared. But the case is different with the Moorhens; they remain in or near their territory throughout the year, and if they allowed the young to remain with them it is unquestionable that, as the sexual instinct arose the following spring, they would have serious rivals in their offspring, by that time fully developed, and in strength equal to themselves. There is much evidence to show that in many cases parental affection is limited to the period in which the young are helpless, and so the natural result of the law of territory would be the banishment of the young; and if in addition the habit was of indirect benefit to a species by preventing interbreeding, or by securing an ample supply of food, then it would be fostered by selection and developed in so far as it was beneficial.

What, then, is the meaning of this law of territory? Why should one male struggle so fiercely with another for a small plot of ground? It is claimed only at the breeding season; it is adhered to in many cases only so long as there is a nest and eggs or young within its limits; it is of such importance to the individual male that it may even lead to