The universal geography : earth and its inhabitants

CLIMATE, FAUNA, AND FLORA. 441
suppose that even a single species has been exterminated. The species of birds are
three times more numerous than the species of all otlicr vertebrate animals together,
but three-fourths of these are merely birds of passage or occasional visitors, which
make their home in Switzerland during w^ter or summer. Looking to the geo-
graphical position of Switzerland, in the verj' centre of the temperate zone, and to
its bold mountain ranges, it is easily understood why so large a variety of birds of
passage should temporarily stay in its valleys. These birds, when crossing from
one slope of the Alps to the other, will naturally seek out the lowest depressions
and the Pass of St. Gotthard, with the valley of the Rcuss leading up to it from the
north, and that of the Ticino from the south, forms one of the great high-roads
most frequented by those winged migrants. The high valleys at Urseren and
Andermatt afford convenient resting-places, and it is there that Swiss ornitholo-
gists have captured some of their most valued specimens. These birds, indeed,
pointed out to man, long before Alpine roads were thought of, the easiest passages
across the mountains.
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