Thus, elephants, bears, foxes, and numbers
of species of rodents, very rarely breed in confinement; while other
species do so more or less freely. Hawks, vultures, and owls hardly ever
breed in confinement; neither did the falcons kept for hawking ever
breed. Of the numerous small seed-eating birds kept in aviaries, hardly
any breed, neither do parrots. Gallinaceous birds usually breed freely
in confinement, but some do not; and even the guans and curassows, kept
tame by the South American Indians, never breed. This shows that change
of climate has nothing to do with the phenomenon; and, in fact, the same
species that refuse to breed in Europe do so, in almost every case, when
tamed or confined in their native countries. This inability to reproduce
is not due to ill-health, since many of these creatures are perfectly
vigorous and live very long.
With our true domestic animals, on the other hand, fertility is perfect,
and is very little affected by changed conditions. Thus, we see the
common fowl, a native of tropical India, living and multiplying in
almost every part of the world; and the same is the case with our
cattle, sheep, and goats, our dogs and horses, and especially with
domestic pigeons.
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