gnacious instinct of the male is rendered susceptible to
appropriate stimulation, and the stimulus is supplied by a rival male;
we admit that all the fighting which occurs after pairing has taken
place has nothing to do strictly speaking with gaining a mate, but,
inasmuch as the fact of possession is always liable to be
challenged--and no male can differentiate between a paired and an
unpaired intruder--we contend that it would add to the security of
possession if the pugnacious instinct remained susceptible to
stimulation so long as there were any possibility of challenge from an
unpaired male; and we think that the waste of energy involved in the
struggles between paired birds, and which we grant is purposeless, would
be more than balanced by the added security." This is a possible
explanation and requires consideration. It cannot account for all the
diverse ways in which the sexes are mixed up in the fighting--it cannot,
for instance, explain the fact that an unpaired male will attack either
sex of an adjoining pair indiscriminately--but nevertheless it appears
at first sight to be a reasonable explanation of some of them. We must
remember, however, that fighting continues throughout the whole period
of reproduction. Even after the discharge of the sexual function has
ceased, and the female is engaged in incubation or in tending her young,
the male is still intolerant of intruders; and it is difficult to
believe that, at so late a stage in the process, a female could be any
attraction sexually to an unpaired male. But apart from any theoretical
objection, there remains the fact--namely that there is no evidence
that a male, after having once paired, is liable to be robbed of its
mate. And in support of this fact I have only to state that I have met
with no single instance of failure to obtain and hold a mate when once a
territory had been secured. Bearing in mind then that both sexes
participate in the fighting, and that individuals of the opposite sex
frequently attack one another; that all such conflicts are characterised
by persistent effort, and that they are not limited to just the
particular period when the sexual instinct is dominant but continue
throughout the breeding season; bearing in mind that in at least one
form of this promiscuous warfare the influence of the female can be
definitely excluded, and that, in the remaining forms, the evidence
which is required to link them up with the biological end of secu