y content to remain in isolation, but so behaves that
isolation is insured. Intolerant of the approach of a stranger,
intolerant even of the approach of the very members of the community
whose companionship was previously welcomed, it not only fights to
maintain the position it has selected, but fights indeed for the
possession of ground already occupied, and, until reproduction is
completed, asserts its individuality and exercises dominion over its
territory. What, then, is the prospective value, biologically
considered, of the changing interest that A displays in B, and to what
will such changes lead? These are the questions to which we will now
direct inquiry.

The annual life-history of a bird is in broad outline conditioned by
two powerful and at first sight opposing impulses--the one to live in
society, the other to live solitary. But, manifestly, a bird cannot be
governed by opposing impulses. It has but one character, within which,
according to the season and the circumstances, different impulses
predominate. But these impulses, no matter how different they may appear
to be, have their respective parts to play in furthering the life of the
individual. Hence they cannot oppose, though they may conflict, if the
resultant behaviour contributes towards survival.

The majority of birds live to-day in constant danger from predatory
species, and that this danger was still greater in bygone ages there can
be but little doubt. A curious mode of behaviour of the Curlew,
Whimbrel, and Godwit demonstrates this, for it must be the outcome of
the necessity for constant watchfulness. Whilst resting with its head
turned back and its beak buried in the feathers of the mantle, the bird
constantly moves the axis of its body, so that an observer, if placed in
a direct line behind it, sees at one moment the right eye and at another
the left. No movement of the feet or of the legs is perceptible, and the
shifting of the body continues whether the eyes are open or closed. This
body movement enables the bird to survey a much larger area of ground
than it would otherwise be capable of doing, and thus adds to its
security. As far as my experience goes, the movement is less evident
amongst the members of a flock than when an individual is resting alone,
or even with a few companions, which may be due to the fact that since
some members are always awake and watchful, a bird of prey would have
more difficulty in approaching a flock unaware