The vulture builds its nest on inaccessible cliffs; for which
reason its nest and young are rarely seen. And therefore Herodorus,
father of Bryson the Sophist, declares that vultures belong to some
foreign country unknown to us, stating as a proof of the assertion
that no one has ever seen a vulture's nest, and also that vultures
in great numbers make a sudden appearance in the rear of armies.
However, difficult as it is to get a sight of it, a vulture's nest has
been seen. The vulture lays two eggs.

(Carnivorous birds in general are observed to lay but once a
year. The swallow is the only carnivorous bird that builds a nest
twice. If you prick out the eyes of swallow chicks while they are
yet young, the birds will get well again and will see by and by.)



The eagle lays three eggs and hatches two of them, as it is said
in the verses ascribed to Musaeus:

That lays three, hatches two, and cares for one.

This is the case in most instances, though occasionally a brood of
three has been observed. As the young ones grow, the mother becomes
wearied with feeding them and extrudes one of the pair from the
nest. At the same time the bird is said to abstain from food, to avoid
harrying the young of wild animals. That is to say, its wings blanch,
and for some days its talons get turned awry. It is in consequence
about this time cross-tempered to its own young. The phene is said
to rear the young one that has been expelled the nest. The eagle
broods for about thirty days.

The pigeon, as a rule, lays a male and a female egg, and generally
lays the male egg first; after laying it allows a day's interval to
ensue and then lays the second egg. The male takes its turn of sitting
during the daytime; the female sits during the night. The first-laid
egg is hatched and brought to birth within twenty days; and the mother
bird pecks a hole in the egg the day before she hatches it out. The
two parent birds brood for some time over the chicks in the way in
which they brooded previously over the eggs. In all connected with the
rearing of the young the female parent is more cross-tempered than the
male, as is the case with most animals after parturition. The hens lay
as many as ten times in the year; occasional instances have been known
of their laying eleven times, and in Egypt they actually lay twelve
times. The pigeon, male and female, couples within the year; in
fact, it couples when only six months old. Some assert that
ringdoves and turtle-doves pair and procreate when only three months
old, and instance their superabundant numbers by way of proof of the
assertion. The hen-pigeon carries her eggs fourteen days; for as
many more days the parent birds hatch the eggs; by the end of
another fourteen days the chicks are so far capable of flight as to be
overtaken with difficulty. (The ring-dove, according to all
accounts, lives up to forty years. The partridge lives over
sixteen.) (After one brood the pigeon is ready for another within
thirty days.)

Birds of the pigeon kind, such as the ringdove and the
turtle-dove, lay two eggs at a time; that is to say, they do so as a
general rule, and they never lay more than three. The pigeon, as has
been said, lays at all seasons; the ring-dove and the turtle-dove
lay in the springtime, and they never lay more than twice in the
same season. The hen-bird lays the second pair of eggs when the
first pair happens to have been destroyed, for many of the hen-pigeons
destroy the first brood. The hen-pigeon, as has been said,
occasionally lays three eggs, but it never rears more than two chicks,
and sometimes rears only one; and the odd one is always a wind-egg.

Very few birds propagate within their first year. All birds,
after once they have begun laying, keep on having eggs, though in
the case of some birds it is difficult to detect the fact from the
minute size of the creature.

During the period above referred to the chick
sleeps, wakes up, makes a move and looks up and Chirps; and the
heart and the navel together palpitate as though the creature were
respiring. So much as to generation from the egg in the case of birds.

Birds lay some eggs that are unfruitful, even eggs that are
the result of copulation, and no life comes from such eggs by
incubation; and this phenomenon is observed especially with pigeons.

Twin eggs have two yolks. In some twin eggs a thin partition
of white intervenes to prevent the yolks mixing with each other, but
some twin eggs are unprovided with such partition, and the yokes run
into one another. There are some hens that lay nothing but twin
eggs, and in their case the phenomenon regarding the yolks has been
observed. For instance, a hen has been known to lay eighteen eggs, and
to hatch twins out of them all, except those that were wind-eggs;
the rest were fertile (though, by the way, one of the twins is
always bigger than the other), but the eighteenth was abnormal or
monstrous.

About the twentieth day, if you open the egg and touch the
chick, it moves inside and chirps; and it is already coming to be
covered with down, when, after the twentieth day is ast, the chick
begins to break the shell. The head is situated over the right leg
close to the flank, and the wing is placed over the head; and about
this time is plain to be seen the membrane resembling an after-birth
that comes next after the outermost membrane of the shell, into
which membrane the one of the navel-strings was described as leading
(and, by the way, the chick in its entirety is now within it), and
so also is the other membrane resembling an after-birth, namely that
surrounding the yolk, into which the second navel-string was described
as leading; and both of them were described as being connected with
the heart and the big vein. At this conjuncture the navel-string
that leads to the outer afterbirth collapses and becomes detached from
the chick, and the membrane that leads into the yolk is fastened on to
the thin gut of the creature, and by this time a considerable amount
of the yolk is inside the chick and a yellow sediment is in its
stomach. About this time it discharges residuum in the direction of
the outer after-birth, and has residuum inside its stomach; and the
outer residuum is white (and there comes a white substance inside). By
and by the yolk, diminishing gradually in size, at length becomes
entirely used up and comprehended within the chick (so that, ten
days after hatching, if you cut open the chick, a small remnant of the
yolk is still left in connexion with the gut), but it is detached from
the navel, and there is nothing in the interval between, but it has
been used up entirely.