Page:The British Warblers A History with Problems of Their Lives - 5 of 9.djvu/33

 is more vividly coloured than the male, and it is possibly she who defends the territory, attacks all intruders, and exhibits the pugnacity referred to, although it is difficult to make certain of this, since the difference in colouring and size between the sexes is so slight that at a distance it is not very easy to distinguish them. The question we are attempting to answer is what is the cause of the battles, and whether an individual of one sex does really struggle for possession of one of the other sex. When the righting is confined to one sex only, we might be justified, providing there were no evidence to the contrary, in assuming that the opposite sex was the immediate cause. But in the case of the Whitethroat we have a species in which the males are more brightly coloured than the females and struggle amongst themselves, but in which, contrary to expectation, the females also fight with one another. Of what advantage could it be to any species for the males to struggle for the females, and for the females to struggle for the males? This fact of the females fighting is therefore one of some importance, since it points to the existence of some other factor as the true cause of the battles. Among the large number of individuals that annually migrate together, it must sometimes happen that two females settle in the same occupied territory, and under these circumstances what could be more natural than that one should attempt to drive the other away? The ultimate object of such a battle may be said to be the male: this much I concede; but another factor is introduced by the law of territory, with the result that it matters not whether the male possesses any special attractiveness, so long as the more important consideration be fulfilled, namely, that he be the owner of a territory. The question, then, which remains to be answered is to what extent a law of battle does exist amongst the females. I mentioned at the time that in no other species had I seen the females fighting, but I have since been lucky enough to see two more instances. Both sexes of the Moorhen aid in the defence of their territory, as do both sexes of