into warmer climates in
winter, if such places are at no great distance; if they are, they bury
themselves in the climates where they dwell," (8. Hist. c. 16. See also
Derham's Phys. Theol. v. ii. p. 177.)

Hence their emigrations cannot depend on a _necessary_ instinct, as the
emigrations themselves are not _necessary_.

2. When the weather becomes cold, the swallows in the neighbourhood
assemble in large flocks; that is, the unexperienced attend those that have
before experienced the journey they are about to undertake: they are then
seen some time to hover on the coast, till there is calm whether, or a
wind, that suits the direction of their flight. Other birds of passage have
been drowned by thousands in the sea, or have settled on ships quite
exhausted with fatigue. And others, either by mistaking their course, or by
distress of weather, have arrived in countries where they were never seen
before: and thus are evidently subject to the same hazards that the human
species undergo, in the execution of their artificial purposes.

3. The same birds are emigrant from some countries and not so from others:
the swallows were seen at Goree in January by an ingenious philosopher of
my acquaintance, and he was told that they continued there all the year; as
the warmth of the climate was at all seasons sufficient for their own
constitutions, and for the production of the flies that supply them with
nourishment. Herodotus says, that in Libya, about the springs of the Nile,
the swallows continue all the year. (L. 2.)

Quails (tetrao corturnix, Lin.) are birds of passage from the coast of
Barbary to Italy, and have frequently settled in large shoals on ships
fatigued with their flight. (Ray, Wisdom of God, p. 129. Derham. Physic.
Theol. v. ii. p. 178,) Dr. Ruffel, in his History of Aleppo, observes that
the swallows visit that country about the end of February, and having
hatched their young disappear about the end of July; and returning again
about the beginning of October, continue about a fortnight, and then again
disappear. (P. 70.)

When my late friend Dr. Chambres, of Derby, was on the island of Caprea in
the bay of Naples, he was informed that great flights of quails annually
settle on that island about the beginning of May, in their passage from
Africa to Europe. And that they always come when the south-east wind blows,
are fatigued when they rest on this island, and are taken in such amazing
quantities and sold to th