yet in no single instance did I hear the true song uttered on the feeding ground, although the moment a male returned to its territory its monotonous croak could be heard, uttered moreover with that persistence which is so marked a feature of all song or of the sounds that correspond to it.
Thus it will be seen that, even after the internal organic changes have taken place, the instinct of song is not susceptible to stimulation at all times and under all circumstances, but only at certain specified times and under special circumstances which can be observed to correspond with the occupation of the territory.
In many species each male singles out within its territory some prominent position to which it resorts with growing frequency. This position is an important feature of the territory, and exercises a dominating influence on the life of the bird. I have referred to it as the "headquarters," and it may be a solitary tree or bush, an outstanding mound or mole hillock, a gatepost or a railing—anything in fact that supplies a convenient resting place so long as it fulfils one condition, namely that the bird when it is there is conspicuous. It need not, however, be a tree or a mound or indeed anything upon which the bird can perch, for there is reason to think that the soaring flight undertaken at this season by so many males, since it is generally accompanied by the specific sexual sound,
