less for the young. If, then, there were nothing to
prevent this happening, many of the birds in that marsh would have no
chance of rearing their young successfully. Hence, if the territory is
adequately to serve the purpose for which we believe it has been
evolved, some provision must have been included in the system to meet
the difficulty.

There are three ways by which this may have been
accomplished--indirectly, by increasing the size of the area occupied by
each individual, and thereby reducing the relative number of each
species; or directly, by rendering the fighting instinct of the bird
susceptible to stimulation by individuals of other species; or,
possibly, by a combination of the two. There were four pairs of
Reed-Buntings in the marsh, and their territories covered the whole of
it. But inasmuch as other insectivorous birds were established there
also, and found sufficient food to maintain both themselves and their
families, it is clear that the area these Reed-Buntings occupied was in
excess of that which they would have required if they had been the sole
inhabitants. And such often appears to be the case. Many a Warbler
allocates to itself a space of ground more than sufficient to supply it
with all that it needs; so, too, does the Finch, or the Pipit, or the
Falcon--if we take no account of kindred species. Thus there is reason
to believe that, by limiting the number of individuals in a given
locality, this apparently wasteful expanse of territory is serviceable
in that it provides against the pressure of the bird population upon the
available means of support becoming too great. But though a reduction in
the numerical standing of the different species would certainly follow
from any increase in the area occupied by the respective individuals,
and with even greater certainty would place them in a more secure
position as regards their supply of food, yet, when we remember how
large a number are dependent upon a supply of insect life for their
young, we can understand that it would not alone be a sufficient
safeguard against the dangers attendant upon overcrowding. It is here, I
believe, that we shall find the true explanation of the hostility; it
roughly insures that the number of pairs in any given area does not
exceed the available means of support, and indeed it is difficult to
imagine how such uniformity of distribution as would free the young from
the risk of exposure could be obtained without some suc