normal routine of existence, and to meet all
exigencies as they arise in their ordinary daily life--whilst free to do
this, their future, as a pair, is nevertheless secure.

Thus far we have considered the territory in its relation to the
discharge of the sexual function. In many of the lower forms of life,
the success or the failure of reproduction, so far as the individual is
concerned, may be said to end with the completion of the sexual act--the
female has but to deposit her eggs in a suitable environment and then
her work is done, because in due course and under normal conditions of
temperature the young hatch out, and from the first are able to fend for
themselves. And so, when we come to consider the question of
reproduction in the higher forms of life, we are apt to focus attention
too much upon the sexual function and too little upon the contributory
factors, the failure of any one of which would mean failure of the
whole. For a bird, success in the attainment of reproduction does not
merely imply the successful discharge of the sexual function; much more
is demanded; it must find somewhere to build its nest and to lay its
eggs, it must shield its young from extremes of temperature and protect
them from enemies, and it must be in a position to supply them with food
at regular intervals. And, consequently, every situation is not equally
favourable for rearing young; there must be a plentiful supply of food
of the right kind in the immediate vicinity of the nest, and it must be
in greatest abundance just at the moment when it is most urgently
needed--that is to say, during the first few weeks after the birth of
the young. Success, therefore, depends upon manifold relationships which
centre in the station, and these relationships vary in intensity with
the conditions of existence.

First, then, let us examine the problem from the point of view of the
food-supply. There are many species whose success in rearing offspring
is largely dependent upon the rapidity with which they can obtain food;
and it makes but little difference which species we choose out of
many--Finch, Bunting, Warbler, or Chat. I shall choose the Buntings, as
their life-history in broad outline conforms to the general type, and,
moreover, their behaviour is fresh in my mind. The young are born in a
very helpless state; they are without covering--fragile organisms,
ill-fitted, one would think, to withstand extremes of temperature, and
wholly inca