growth, or to the hole
excavated with such skill in the tree trunk; to the beautifully shaped
eggs; to the parent birds carrying out their work with devoted zeal--in
fact, to the whole series of events which complete the sexual life of
the individual; and the attachment of a particular bird to a particular
spot is readily accounted for in terms of one or other of the emotions
which centre round the human home.

But if this behaviour is to be understood aright; if, that is to say,
the exact position it occupies in the drama of bird life is to be
properly determined, and its biological significance estimated at its
true value, it is above all things necessary to refrain from appealing
to any one of the emotions which we are accustomed to associate with
ourselves, unless our ground for doing so is more than ordinarily
secure. I shall try to show that, in the case of many species, the male
inherits a disposition to secure a territory; or, inasmuch as the word
"secure" carries with it too much prospective meaning, a disposition to
remain in a particular place when the appropriate time arrives.

If the part which the breeding territory plays in the sexual life of
birds is the important one I believe it to be, it follows that the
necessary physiological condition must arise at an early stage in the
cycle of events which follow one another in ordered sequence and make
towards the goal of reproduction, and that the behaviour to which it
leads must be one of the earliest visible manifestations of the seasonal
development of the sexual instinct. When does this seasonal development
occur? For how long does the instinct lie dormant? In some species there
is evidence of this first step in the process of reproduction early in
February; there is reason to believe that in others the latter part of
January is the period of revival; and the possibility must not be
overlooked of still earlier awakenings, marked with little definiteness,
though nevertheless of sufficient strength to call into functional
activity the primary impulse in the sexual cycle. Here, then, we meet
with a difficulty so far as direct observation is concerned, for the
duration of the period of dormancy and the precise date of revival vary
in different species; and, if accurate information is to be obtained,
the study of the series of events which culminate in the attainment of
reproduction ought certainly to begin the moment behaviour is
influenced by the internal cha