apidity with which the female
can discover a male fit to breed; for if the course of reproduction is
to flow smoothly, there must be neither undue delay nor waste of energy
incurred in the search--some guidance is therefore necessary, some
control in her external environment. Here the song, or the mechanically
produced sound, comes into play, and assists in the attainment of this
end. Nevertheless if every male were to make use of its powers whether
it were in occupation of a territory or not, if the wandering individual
had an equal chance of attracting a mate, then it would be idle to
attempt to establish any relation between "song" on the one hand, and
"territory" on the other, and impossible to regard the voice as the
medium through which an effectual union of the sexes is procured. But
there is reason to believe that the males utilise their powers of
producing sound only under certain well-defined conditions. For
instance, when they are on their way to the breeding grounds, or moving
from locality to locality in search of isolation, or when they desert
their territories temporarily, as certain of the residents often do,
they are generally silent; but when they are in occupation of their
territories they become vociferous--and this is notoriously the case
during the early hours of the day, which is the period of maximum
activity so far as sexual behaviour is concerned. So that just at the
moment when the sexual impulse of the female is most susceptible to
stimulation, the males are betraying their positions and are thus a
guide to her movements. Nevertheless, even though she may have
discovered a male ready to breed, success is not necessarily assured to
her; for with multitudes of individuals striving to procreate their
kind, it would be surprising if there were no clashing of interests, if
no two females were ever to meet in the same occupied territory.
Competition of this kind is not uncommon, and the final appeal is to the
law of battle, just as an appeal to physical strength sometimes decides
the question of the initial ownership of a territory.

I shall try to make clear the relations of the various parts to the
whole with the assistance of whatever facts I can command. I shall do so
not only for the purposes of the theory, but because one so often finds
the more important features of sexual behaviour regarded as so many
distinct phenomena requiring separate treatment, whereas they are
mutually dependent, and