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.
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