s than it would have in
approaching a single individual. With the greatest ease a Sparrow-Hawk
can pick up a Thrush as it feeds on the meadow by itself, but if it
attempts to seize one of a flock, the chances are that its approach is
signalled and that its prey escapes. And not only do the different
members give warning one to another of the approach of danger, but they
also combine to harass or even to drive away an enemy. So that there can
be no doubt that the gregarious instinct is serviceable in promoting the
welfare of the race, and has, as its end, the preservation of the
individual in order that it may take its share at the appropriate time
in procreating its kind.

In winter, then, the individual loses its individuality and is
subordinated to the welfare of the community, whilst in spring it
regains its individuality, and all its inherited instincts which then
come into operation lead to its isolation from the flock. The impulse to
seek isolation is dependent upon internal organic conditions which are
peculiar to a certain season; whereas the gregarious impulse depends
upon internal organic conditions which inhere at all times, though its
functioning is inhibited by the functioning of the former impulse. The
evidence which leads to this conclusion is to be found in the fact that
a male often deserts its territory temporarily and joins the flock,
where it remains at peace with its companions--an aspect of behaviour
which we have discussed on various occasions. The former impulse becomes
dominant in the spring owing to its innately superior strength; the
latter becomes dominant in the autumn because the organic condition
which determines the functioning of the former then subsides. The
impulse to seek the appropriate breeding ground and to dwell there would
seem to be the strongest of all the impulses save one--the sexual.
When, however, I speak of the sexual, I refer to the actual discharge of
the sexual function, which is the consummation of the whole process. But
the territory and all that appertains to it is part of that process--the
search for the breeding ground, the dwelling there, and the intolerance
of intrusion are but different stages, each one of which must have an
impulse peculiar to it; and since the completion of the sexual act can
only be successfully accomplished providing that success is attained at
every stage, the probability is that, of the impulses concerned, one is
neither more powerful nor