ourse is discovered by a female. The whole is thus an inter-related
whole, a chain of activities which follow one another in ordered
sequence. Now we have seen that it is neither pugnacious nor vociferous
until the territory is actually occupied; we have seen that the fact of
occupation is the condition under which the instincts of pugnacity and
of song are rendered susceptible to appropriate stimulation; we have
discussed the nature of the stimulus in each case, and we wish to know
the sort of meaning that the song conveys to an individual which is
still in the preliminary stage of seeking a station. In sequential order
we have the following: (1) internal organic changes which lead to
isolation, (2) the appropriate environment which gives rise to an
impulse to remain in it, (3) the occupation of a territory which is the
condition under which the instincts are rendered susceptible to
stimulation, (4) the various stimuli. Each is dependent upon that which
precedes it, and no part can be subtracted without failure of the
biological end in view, neither can the different stages be combined in
different order. So that, in considering the significance of song to an
unestablished male, we are dealing with the situation at a point at
which all the latent activities have not been fully felt, for all that
so far has occurred is the change from sociability to isolation
determined by internal organic changes. The bird has not established a
territory because it has not come into contact with the appropriate
environment, and it is not pugnacious because the condition which
renders its instinct susceptible is absent; and so, as it wanders from
place to place and hears the voices of males here or males there, it
merely behaves in accordance with that part of its nature which
predominates just at that particular moment--the impulse to avoid them.

But given the appropriate environment, given, that is to say, just that
combination of circumstances which might bring into functional activity
all the latent instincts of the intruder, and no matter how vociferous
the occupant of a territory might be, it would not be preserved from
molestation. The advantage of the song, biologically considered, is then
this, that it will often prove just sufficient to preclude males in
search of isolation from coming into contact with the environmental
conditions adequate to supply the stimulus to their latent activities
and to convert them into rivals.

I