Again, as the average number of young produced is four or five times
that of the parents, we ought to have at least five times as many birds
in the country at the end of summer as at the beginning, and there is
certainly no such enormous disproportion as this. The fact is, that the
destruction commences, and is probably most severe, with nestling birds,
which are often killed by heavy rains or blown away by severe storms, or
left to die of hunger if either of the parents is killed; while they
offer a defenceless prey to jackdaws, jays, and magpies, and not a few
are ejected from their nests by their foster-brothers the cuckoos. As
soon as they are fledged and begin to leave the nest great numbers are
destroyed by buzzards, sparrow-hawks, and shrikes. Of those which
migrate in autumn a considerable proportion are probably lost at sea or
otherwise destroyed before they reach a place of safety; while those
which remain with us are greatly thinned by cold and starvation during
severe winters. Exactly the same thing goes on with every species of
wild animal and plant from the lowest to the highest.
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