ng a
headquarters, the male and female are allowed a freedom of movement
which otherwise they would only possess when the construction of the
nest had actually begun; they can seek their food independently, and,
even though paired, they can if necessary continue their winter routine
without risk of separation. This means that the organic condition which
leads to pairing, is free to develop in the female earlier than would be
the case if there were nothing in the external environment to attract
the pair to a particular spot; and the longer the period over which the
process of pairing can be spread, the greater chance will females have
of discovering mates, the less severe will the competition tend to
become, and, consequently, the smaller the percentage of individuals
that fail to obtain suitable partners.

In these ways the territory has been serviceable alike to a number of
species. But much as the questions of mutual discovery and regular
distribution may have influenced the course of its development, there
can, I think, be little doubt that, on the one hand, the supply of the
necessary accommodation for rearing offspring, and on the other, the
necessity for an adequate supply of food in close proximity to the nest,
have been the main determining factors, and have led to a wide
divergence in its function. At the one extreme the function is to insure
a plentiful supply of food for the young; at the other, to insure a
station suitable for rearing offspring. I took the Bunting and the
Guillemot as types of the two extremes. The young of the former species
are born in a very helpless state. They are susceptible to cold and
unable to withstand prolonged exposure, and therefore it is essential
that there should be an ample supply of food, upon which the parents can
draw liberally, in the vicinity of the nest. But the nest is placed in a
variety of situations, and accommodation in this respect may be said to
be unlimited. The young of the latter species are not so susceptible to
exposure, and moreover there is always an abundance of food in the
waters beneath the cliff; but ledges of rock, upon which the egg can be
securely deposited and the young successfully reared, are limited both
in number and extent. The position then is as follows: there are
situations in plenty in which hosts of Buntings can build their nests
but the supply of food is a difficulty, and if the respective areas of
different individuals were insufficien