eturns, and after a while repeats the
performance; we on our part mark the extreme limits reached in each
direction, and by continued observation discover that these limits are
seldom exceeded, that definition grows more and more pronounced, and
that by degrees the movements of the bird are confined within a
restricted area. In outline, this is what happens in a host of cases. By
repetition certain performances become stereotyped, certain paths fixed,
and a routine is thus established which becomes increasingly definite as
the season advances.

But while it would be quite untrue to say that this routine is never
departed from, and equally profitless to attempt to find a point beyond
which the bird will under no circumstances wander, yet there is enough
definition and more than enough to answer the purpose for which the
territory has, I believe, been evolved, that is to say the biological
end of reproduction. Again, however, the process of adjustment is a
complex one. Habit plays its part in determining the boundaries in a
rough and ready manner, but the congenital basis, which is to be found
in the behaviour adapted to a particular environment, is an important
factor in the situation. For example, if instead of resting content with
just a bare position sufficient for the purpose of reproduction, the
Guillemot were to hustle its neighbours from adjoining ledges, the
Guillemot as a species would probably disappear; or if instead of
securing an area capable of supplying sufficient food both for itself
and its young, the Chiffchaff were to confine itself to a single tree,
and, after the manner of the Guillemot, trust to spasmodic excursions
into neutral ground for the purpose of obtaining food, the Chiffchaff
as a species would probably not endure. All such adjustments have,
however, been brought about by relationships which have gradually become
interwoven in the tissue of the race.

The intolerance that the male displays towards other individuals,
usually of the same sex, leads to a vast amount of strife. Nowhere in
the animal world are conflicts more frequent, more prolonged, and more
determined than in the sexual life of birds; and though they are
acknowledged to be an important factor in the life of the individual,
yet there is much difference of opinion as to the exact position they
occupy in the drama of bird life. Partly because they frequently happen
to be in evidence, partly because they are numerically inferior,