It 
TIIK STRUGGLE FOR EXISTENCE 
33 
instead of a diminution of this prodigious procession, it seemed 
rather to increase, both in numbers and rapidity ; and anxious 
to reach Frankfort before night, I rose and went on. About 
four o’clock in the afternoon I crossed Kentucky River, at the 
town of Frankfort, at which time the living torrent above my 
head seemed as numerous and as extensive as ever. Long 
after this I observed them in large bodies that continued to 
pass for six or eight minutes, and these again were followed 
by other detached bodies, all moving in the same south-east 
direction, till after six o’clock in the evening. The great 
breadth of front which this mighty multitude preserved would 
seem to intimate a corresponding breadth of their breeding- 
place, which, by several gentlemen who had lately passed 
through part of it, was stated to me at several miles. ’ 
From these various observations, Wilson calculated that 
the number of birds contained in the mass of pigeons which 
he saw on this occasion was at least two thousand millions, 
while this was only one of many similar aggregations known 
to exist in various parts of the United States. The 
picture here given of these defenceless birds, and their still 
more defenceless young, exposed to the attacks of numerous 
rapacious enemies, brings vividly before us one of the phases 
of the unceasing struggle for existence ever going on ; but 
when we consider the slow rate of increase of these birds, 
and the enormous population they are nevertheless able to 
maintain, we must be convinced that in the case of the 
majority of birds which multiply far more rapidly, and yet 
are never able to attain such numbers, the struggle against 
their numerous enemies and against the adverse forces of 
nature must be even more severe or more continuous. 
Struggle for Life between closely allied Animals and Plants 
often the most severe. 
The struggle we have hitherto been considering has been 
mainly that between an animal or plant and its direct enemies, 
whether these enemies are other animals which devour it, or 
the forces of nature which destroy it. But there is another 
kind of struggle often going on at the same time between 
closely related species, which almost always terminates in the 
destruction of one of them. As an example of what is 
D 
