DARTFORD WARBLER
stimulus to the emotional manifestation in the male was supplied directly by them. Let us examine these emotional scenes more closely. Sexual no doubt they are in origin, in so far as the sexual instinct is the source of all this behaviour, but the instinct more immediately aroused is clearly that of pugnacity. There is a deal of quarrelling and sometimes much fighting. The males follow one another closely from bush to bush, and meeting upon the top of some holly or fir tree or prominent gorse bush, utter their scolding note, warble, or sing, with their feathers in the meantime tightly compressed. And when the scene becomes more animated, both males, at different moments or perhaps together, expand one wing and hold it momentarily fully expanded, or expand both wings alternately with great deliberation. The expansion of one wing can be frequently witnessed and may occur whilst the birds are on the ground hopping round and about one another. At any moment, too, their emotions may increase in intensity until the situation becomes one of active hostility. Thereupon they fly at one another often amongst the thick heather, and one can hear the snapping of bills and observe scenes which are customarily associated with hostility. What relation can these activities bear to the female if the males that take part in them are paired and have each their respective mates? I have even observed a male desert the company of his female, when another male was close at hand, and become an actor in such a scene, so that we cannot regard the presence of an unpaired male as an essential condition of the situation, if, that is to say, my observations are correct. In the absence of sufficient data, one is forced to bring to bear upon the problem knowledge derived from other species. And knowing the part that the struggle for territory plays in the lives of so many different species, we are justified, I think, in believing that it is responsible for the manifestations which we witness.
I mentioned the expansion of one wing or the alternate expansion of both wings in the case of the male during periods
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