"The condor lays a couple of eggs, and the ostrich a score; and yet in the
same country the condor may be the more numerous of the two. The Fulmar
petrel lays but one egg, yet it is believed to be the most numerous bird in
the world."--(p. 68.)

"The amount of food gives the extreme limit to which each species can
increase; but very frequently it is not the obtaining of food, but the
serving as prey to other animals, which determines the average numbers of
species."--(p. 68.)

"Climate plays an important part in determining the average numbers of a
species, and periodical seasons of extreme cold or drought I believe to be
the most effective of all checks. I estimated that the winter of 1854--'55
destroyed four-fifths of the birds in my own grounds; and this is a
tremendous destruction, when we remember that ten per cent, is an
extraordinarily severe mortality from epidemics with man. The action of
climate seems at first sight to be quite independent of the struggle for
existence; but, in so far as climate chiefly acts in reducing food, it
brings on the most severe struggle between the individuals, whether of the
same or of distinct species, which subsist on the same kind of food, Even
when climate, for instance extreme cold, acts directly, it will be the
least vigorous, or those which have got least food through the advancing
winter, which will suffer most. When we travel from south to north, or from
a damp region to a dry, we invariably see some species gradually getting
rarer and rarer, and finally disappearing; and, the change of climate being
conspicuous, we are tempted to attribute the whole effect to its direct
action. But this is a very false view; we forget that each species, even
where it most abounds, is constantly suffering enormous destruction at some