The former evokes the normal reply, that is to say the bird, if silent, is liable to utter a corresponding reply; the latter arouses hostility into which is infused much feeling tone, the bird sings hurriedly while in pursuit of its rival, and, which is more remarkable still, even in the midst of an encounter. Both the normal reply and the emotional song must be similar in origin—different aspects of the same situation—and both are clearly related to the other male.
The arrival of a female may also be followed by an emotional outburst which can be heard at intervals for some days; on the other hand, the song may continue as before or, for a time, entirely cease.
To take the emotional outburst first. This would appear to be susceptible of explanation on the hypothesis that the voice contributes to a more effective pairing situation; an hypothesis which admittedly, at first sight, gains some support from the fact that a second or a third male is frequently present. But, in truth, the presence of a second male makes the situation, so far as the relationship between the song and the female is concerned, all the more perplexing; for, as we have already seen, the instinct of pugnacity, when aroused by the appearance of an intruder, is also liable to be accompanied by a similarly extravagant song. On each occasion the vocal effort is infused with much feelling tone, and it would be impossible to point to any one feature which is peculiar to only one
