dvantage from the
additional space over which they exercised dominion, but inasmuch as
many members that were fitted to breed would be precluded from doing
so, the status of the species as a whole would be seriously affected.
The amount of space occupied by each individual is therefore a matter of
urgent importance. A few square feet of rock sufficient for the
immediate purpose of incubation is all that can be allowed if the
species is to maintain its position in the struggle for existence.

Our difficulty in estimating the importance of the various factors that
make for success or failure arises from our inability to see more than a
small part of the scene as it slowly unfolds itself. The peculiar
circumstances under which these cliff-breeding forms dwell does,
however, enable us to picture, on the one hand, the precarious situation
of an individual that was incapable of winning or holding a position at
the accustomed breeding station, and, on the other, the plight of the
species as a whole if each one exercised authority over too large an
area. With the majority of species it is difficult to do this. So many
square miles of suitable breeding ground are inhabited by so few
Reed-Buntings that, even supposing certain members were to establish an
ascendency over too wide an area, it would be impossible to discover by
actual observation whether the race as a whole were being adversely
affected. Competition doubtless varies at different periods and in
different districts according to the numerical standing of the species
in a given locality and according to the numerical standing of others
that require similar conditions of existence; at times it may even be
absent, just as at any moment it may become acute. These examples show
how profoundly the evolution of the breeding territory may have been
influenced by relationships in the inorganic world, and they give some
idea of the intricate nature of the problem with which we have to deal.

I mentioned that the first visible manifestation of the revival of the
sexual instinct was to be found in the movements undertaken by the males
at the commencement of the breeding season. Such movements are
characterised by a definiteness of purpose, whether they involve a
protracted journey of some hundreds of miles or merely embrace a parish
or so in extent, and that purpose is the acquirement of a territory
suitable for rearing offspring. They are thus directly related to the
territory,