f this interpretation be correct, if we are right in attributing the
withdrawal solely to the fact that the first stage only in the
relational series has been reached, it follows that the effect of song
upon males that have reached subsequent stages in that series must be of
a very different kind. We have dealt with the male when in the
preliminary stage of seeking isolation, we must deal with it now when
eventually it occupies a territory. How does it behave when it hears, as
it is bound to do, the voices of rivals in its neighbourhood? You may
remember that some allusion was made to the fact that an outburst of
song from one individual was followed, not unfrequently, by a similar
outburst on the part of other individuals in the immediate locality. For
example, silence may reign in the reed-bed except for an occasional note
of the Reed-Warbler or Sedge-Warbler. Suddenly, however, a dispute
arises between two individuals, accompanied by a violent outburst of
song, and forthwith other males in the vicinity begin to sing excitedly
and continue doing so for some minutes in a strangely vigorous manner,
the tumult of voices affording a striking contrast to the previous
silence. Spasmodic outbursts of this kind, stimulated by an isolated
utterance, are by no means uncommon. But not only does song stimulate
song; under certain conditions it has the still more remarkable effect
of arousing hostility. The boundary that separates two adjoining
territories is by no means a definite line, but rather a fluid area
wandered over by this owner at one moment, by that at another. Now so
long as the bird is silent while in this area, the probability is that
it will escape detection and remain unmolested; let it however sing--it
often does so--and it will not merely be approached but attacked, and
consequently this area is the scene of much strife. The point to be
noticed here is that the song brings about no withdrawal; it elicits a
response, attracts instead of repelling, and, in short, arouses the
impulse that is always predominant in the nature of the male when
eventually it occupies a territory--the impulse of self-assertiveness.
Therefore it seems clear that the different stages in the process of
reproduction mark the appearance of different conditions, each of which
renders some new impulse susceptible to stimulation, and that the
significance of song depends upon the stage which happens to have been
reached. Hence when we speak of so