king
exemplification of the law of a limited specific range; for the common
grouse (_Tetra scoticus_) occurs nowhere in the known world except in
the British isles.

Some species of the vulture tribe are said to be cosmopolites; and the
common wild goose (_Anas anser_, Linn.), if we may believe some
ornithologists, is a general inhabitant of the globe, being met with
from Lapland to the Cape of Good Hope, frequent in Arabia, Persia,
China, and Japan, and in the American continent from Hudson's Bay to
South Carolina.[900] An extraordinary range has also been attributed to
the nightingale, which extends from western Europe to Persia, and still
farther. In a work entitled Specchio Comparativo,[901] by Charles
Bonaparte, many species of birds are enumerated as common to Rome and
Philadelphia: the greater part of these are migratory, but some of them,
such as the long-eared owl (_Strix otus_), are permanent in both
countries. The correspondence of the ornithological fauna of the eastern
and western hemispheres increases considerably, as might have been
anticipated, in high northern latitudes.[902]

_Their facilities of diffusion._--In parallel zones of the northern and
southern hemispheres, a great general correspondence of form is
observable, both in the aquatic and terrestrial birds; but there is
rarely any specific identity; and this phenomenon is truly remarkable,
when we recollect the readiness with which some birds, not gifted with
great powers of flight, shift their quarters to different regions, and
the facility with which others, possessing great strength of wing,
perform their aarial voyage. Some migrate periodically from high
latitudes, to avoid the cold of winter, and the accompaniments of
cold,--scarcity of insects and vegetable food; others, it is said, for
some particular kinds of nutriment required for rearing their young: for
this purpose they often traverse the ocean for thousands of miles, and
recross it at other periods, with equal security.

Periodical migrations, no less regular, are mentioned by Humboldt, of
many American water-fowl, from one part of the tropics to another, in a
zone where there is the same temperature throughout the year. Immense
flights of ducks leave the valley of the Orinoco, when the increasing
depth of its waters and the flooding of its shores prevent them from
catching fish, insects, and aquatic worms. They then betake themselves
to the Rio Negro and Amazon, having passed fro