the coldest as well as the hottest regions, although some species are
restricted to particular countries, whilst others are widely dispersed.
At certain seasons of the year, many of them change their abodes, and
migrate to climates better adapted to their temperaments or modes of
life, for a time, than those which they leave. Many of the birds of
Britain, directed by an unerring instinct, take their departure from the
island before the commencement of winter, and proceed to the more
congenial warmth of Africa, to return with the next spring. The causes
assigned by naturalists for this peculiarity are, either a deficiency of
food, or the want of a secure asylum for the incubation and nourishment
of their young. Their migrations are generally performed in large
companies, and, in the day, they follow a leader, which is occasionally
changed. During the night, many of the tribes send forth a continual
cry, to keep themselves together; although one would think that the
noise which must accompany their flight would be sufficient for that
purpose. The flight of birds across the Mediterranean was noticed three
thousand years ago, as we find it said in the book of Numbers, in the
Scriptures, that "There went forth a wind from the Lord, and brought
quails from the sea, and let them fall upon the camp, and a day's
journey round about it, to the height of two cubits above the earth."