ves so to
regulate the distribution of pairs that the maximum number can be
accommodated in the minimum area. This being so, the question arises as
to whether competition for territory is strictly limited to individuals
of the same species, or whether it may not occur also between different
kinds of birds, providing always that similar conditions of existence
are required. First of all I shall relate a number of facts which will
serve to show the nature and extent of the warfare, and I shall then
give the reasons which lead me to believe that the fighting not only
bears some relation to the "territory," but that it is an important
factor in contributing to the attainment of that which for biological
interpretation is the end for which the whole territorial system has
been evolved.

Those who have studied wild life on one of the rocky headlands, which
are so numerous round our coasts, will probably be familiar with the
rivalry that exists between the Raven and certain birds of prey. Where
the Raven finds shelter for its nest, there, too, the Peregrine has its
eyrie--and so it happens that these two species are continually at war.
Now the warfare occurs not only during the season of reproduction but
continues throughout the greater part of the year, and can even be
observed in the late summer or early autumn--the period when we should
expect to find the instinct least susceptible to appropriate
stimulation. But it is of a more determined kind early in the spring,
and it is then that we often witness those remarkable exhibitions of
flight, the skill of which excites our admiration. The Falcon rises
above the Raven, stoops at it, and when it seems no longer possible for
a collision to be avoided, or, one would imagine, for the Raven to
escape destruction, the Raven skilfully turns upon its back and
momentarily faces its opponent, and the Falcon with equal skill changes
its course, passing upwards and away. The attack, however, is soon
repeated, and though no collision may actually take place, yet the fact
that the Raven, when it turns to face its adversary, is obliged to drop
the stick which it carries, is not only an indication of the character
of the struggle, but it shows that a definite end is gained--that the
efforts of the Raven to build in that particular locality are hampered.
But the Falcon is not the only enemy that the Raven has to face;
Buzzards are just as intolerant of the presence of Ravens in their
neighbou