Many prudent actions appear to be performed by cranes; for they travel
great distances, and fly at a great elevation, in order that they may
see farther; and if they see clouds and wintry weather, they descend
and rest themselves. They have also a leader in front; and in the rear
are those which give a signal by whistling, so that their voice may be
heard. When they settle on the ground, the rest sleep with their head
under the wing, first on one foot, then on the other; but the leader
watches with his neck stretched out, and when he sees anything he gives
a signal by his cry. The pelicans, which inhabit the rivers, swallow
large smooth shells with their drink, and when they have been digested
in the first part of their stomach, they vomit them up, in order that
they may pick out and eat their flesh when they open their valves.