and the question arises as to whether their origin may not be
traced to such relatedness. So long as we fix our attention solely upon
the magnitude of the distance traversed the suggestion may seem a
fanciful one. Nevertheless, if the battles between males of the same
species _are_ directly related to the occupation of a position suitable
for breeding purposes, if those which occur between males of closely
related forms _can_ be traced to a similar source, if the females take
their share in the defence of the ground that is occupied, if, in short,
the competition is as severe as I believe it to be, and is wholly
responsible for the strife which is prevalent at the commencement of the
breeding season--then such competition must have introduced profound
modifications in the distribution of species; it must have even
influenced the question of the survival of certain forms and the
elimination of others; and since the powers of locomotion of a bird are
so highly developed it must have led to an extension of breeding range,
limited only by unfavourable conditions of existence.

CHAPTER II

THE DISPOSITION TO SECURE A TERRITORY

Those who have studied bird life throughout the year are aware that the
distribution of individuals changes with the changing seasons. During
autumn and winter, food is not so plentiful and can only be found in
certain places, and so, partly by force of circumstances and partly on
account of the gregarious instinct which then comes into functional
activity, different individuals are drawn together and form flocks of
greater or less dimensions, which come and go according to the
prevailing climatic conditions. But with the advent of spring a change
comes over the scene: flocks disperse, family parties break up, summer
migrants begin to arrive, and the hedgerows and plantations are suddenly
quickened into life. The silence of the winter is broken by an outburst
of song from the throats of many different species, and individuals
appear in their old haunts and vie with one another in advertising their
presence by the aid of whatever vocal powers they happen to possess--the
Woodpecker utters its monotonous call from the accustomed oak; the
Missel-Thrush, perched upon the topmost branches of the elm,
persistently repeats its few wild notes; and the Swallow returns to the
barn.

All of this we observe each season, and our thoughts probably travel to
the delicate piece of architecture in the under