afterwards know, when they hear this note, though they do not see their
dam, that the presence of their adversary is denounced, and hide themselves
as before.

The wild tribes of birds have very frequent opportunities of knowing their
enemies, by observing the destruction they make among their progeny, of
which every year but a small part escapes to maturity: but to our domestic
birds these opportunities so rarely occur, that their knowledge of their
distant enemies must frequently be delivered by tradition in the manner
above explained, through many generations.

This note of danger, as well as the other notes of the mother-turkey, when
she calls her flock to their food, or to sleep under her wings, appears to
be an artificial language, both as expressed by the mother, and as
understood by the progeny. For a hen teaches this language with equal ease
to the ducklings, she has hatched from suppositious eggs, and educates as
her own offspring: and the wagtails, or hedge-sparrows, learn it from the
young cuckoo their softer nursling, and supply him with food long after he
can fly about, whenever they hear his cuckooing, which Linnæus tells us, is
his call of hunger, (Syst. Nat.) And all our domestic animals are readily
taught to come to us for food, when we use one tone of voice, and to fly
from our anger, when we use another.

Rabbits, as they cannot easily articulate sounds, and are formed into
societies, that live under ground, have a very different method of giving
alarm. When danger is threatened, they thump on the ground with one of
their hinder feet, and produce a sound, that can be heard a great way by
animals near the surface of the earth, which would seem to be an artificial
sign both from its singularity and its aptness to the situation of the
animal.