INCUBATION
“Incubation means lying upon. The brooding bird does in fact crouch or
lie upon her eggs, warming them with the heat of her body for a number
of days with indefatigable patience. When a hen wishes to set, [1] she
makes it known by her repeated cluckings, little cries of maternal
anxiety, by her ruffled feathers, her restless movements, and
particularly by the perseverance with which she stays on the nest, even
when it has no eggs, where she has been in the habit of laying.
“Some hens with wandering dispositions go back to the instincts of
their wild race. They leave the hen-house and seek a hedge or thicket,
where they select a hiding-place to suit them, and there make a little
hollow in the earth which they line as well as they can with a mattress
of dry grass, leaves, and feathers. That is a nest in the rough,
without art, a shapeless construction in comparison with the clever
masterpiece of the chaffinch and goldfinch. It is, furthermore, worthy
of remark that all the domestic birds, as if man’s intervention had
destroyed their skill by freeing them from want, fail to display in the
construction of their nests the admirable resourcefulness shown by most
wild birds. Here might be repeated the saying, as true for man as for
beast, necessity is the mother of invention. Sure of finding, when the
time comes for laying, the basket stuffed with hay by the hand of the
housewife, the domestic fowl does not trouble herself to build a nest,
an undertaking in which the tiniest bird of the fields shows itself a
consummate architect. At the most, when her adventurous disposition
makes her prefer the perilous shelter of the hedge to the safe retreat
of the poultry-yard, the hen, gleaning with her beak a few straws and
leaves, and plucking, if need be, some of her own feathers, succeeds in
making, for her period of brooding, a disordered heap rather than a
nest. There, every day, unknown to all, she goes and lays her egg. Then
for three whole weeks she is not to be seen, or only at intervals. That
is the time of incubation. At last, some fine day, she reappears, very
proud, at the head of a family of young chickens, peeping and pecking
around her.”
“I should like,” said Emile, “to have some hens that set like that in
the fields and then come home again some day with their family of
little chickens.”
“I must admit it is a sight worthy of interest, that of a hen that has
stolen her nest returning to the farmhouse at the head of her newly
hatched young chickens. Her eyes shine with satisfaction; her clucking
has something joyful about it. ‘Look,’ she seems to say to those who
welcome her, ‘see how fine, alert, and vigorous these young chickens
are; they are all mine; I raised them there all alone in a corner of
the hedge, and now I bring them to you. Am I not a fine hen?’ Yes, my
dear biddy, you are a fine hen, but also an imprudent one. In the
fields prowl the weasel and the marten which, if you are absent a
moment, will suck the blood of your little ones; in the fields the fox
is watching to wring your neck; in the fields there are cold, rain, bad
weather, grave peril for your shivering family. You would do better to
remain at home.
“The greater number follow this prudent advice and do not leave the
poultry-yard. In the semi-obscurity of a sheltered quiet corner is
placed the egg-basket, lined with a bed of hay or of crumpled straw. In
it are put from twelve to fifteen eggs, the largest and freshest being
chosen, and preferably those not more than a week old. If they were two
or three weeks old they would not be sure to hatch, as in many of them
the germ would have become too old and would have lost the power to
develop. These arrangements made, the eggs are left to the setting hen
without being touched again.
“Whoever has not seen a setting hen has missed one of the most touching
sights in this world: the devotion of the mother-bird to her eggs, her
self-forgetfulness even to the point of sacrificing her own life. Her
eyes shine with fever, her skin burns. Eating and drinking are
forgotten, and in order not to leave her eggs a moment a hen might even
let herself die of hunger on the nest if some one did not come every
day and gently take her off and make her eat. Others, less persevering,
leave the basket of their own accord, snatch up a little food, and
immediately go back to the nest.”
“Do hens keep up that tiresome setting very long?” asked Emile.
“It takes twenty or twenty-one days for the young chickens to come out
of the shell. During the whole of that time, night and day, the mother
remains squatting on the eggs, except for the rare moments that she
spares, as if grudgingly, for the necessities of nourishment. Her only
distraction in this complete retirement is to turn the eggs over every
twenty-four hours and change their place, moving those outside into the
center, and vice versa, so that all may have an equal share of heat.
That is a delicate operation, and it must be left to the hen’s care to
move the eggs with her beak. Let us be careful not to interfere with
our clumsy hands, for the bird knows better than we how to manage it.”
“If the hen is so careful to move the eggs every day and give them all
the same amount of heat,” said Jules, “it must be heat alone that makes
them hatch?”
“Yes, my friend, simply the heat of the mother makes the eggs hatch.
That is why the hen can be dispensed with and the eggs hatched by
artificial heat, provided it be well regulated, gentle, and continued
for a long time without interruption. The Egyptians, an ancient people
of great skill, practised this method thousands of years ago. They put
the eggs by hundreds of dozens into a sort of oven gently heated for
three weeks, the period of natural incubation. At the end of that time
the peepings of the countless brood did not fail to announce the
success of the operation.”
“What a big family that oven-hatched brood must have been!” exclaimed
Emile. “It would have taken a hundred hens to set on all the eggs, but
in this way they were all hatched at once.”
“A setting hen ceases to lay, and it was doubtless in order not to
interrupt the beneficent daily production of eggs that the Egyptians
invented artificial incubation in an oven. For the same reason
sometimes with us recourse is had to this means, especially where the
raising of poultry is made a business; only the incubation is no longer
carried out in an oven but in ingeniously contrived incubators. In a
drawer, on a bed of hay, the eggs are placed in a single layer. Above,
and separated from the brooder by a sheet-iron partition, is a bed of
water, which a lamp, kept always alight, warms and maintains at the
temperature that the hen’s body would give; that is to say, forty
degrees centigrade. In twenty-one days under this warm ceiling the eggs
hatch just as they would under the hen.”
“Oh, Uncle,” cried Emile, “I should really like to have an incubator
like that in a corner of my room and watch the progress of the hatching
every day by opening the drawer.”
“What you would like to do, others, more skilful, have already done,
not only opening the drawer but breaking an egg each day so as to see
how things are going. I told you that the germ of the bird is a round
spot of dull white, the cicatricle, which by its mobility is always on
top at the surface of the yolk, no matter what the position of the egg.
After five or six hours of incubation you can already distinguish in
the center of the cicatricle a minute glairy swelling which will be the
head, and a line which will be the backbone. Pretty soon there begins
to beat, at regular intervals, the organ most necessary to life, the
heart, which chases through a network of fine veins the blood formed,
little by little, out of the substance of the yolk, and distributes it
everywhere to furnish materials to the other organs just coming into
being. It is toward the second day that these first heart-beats,
destined to continue henceforth until death, become apparent. Thus
irrigated with running flesh—for blood is nothing else—this organism
thenceforward makes rapid progress. The eyes show themselves and form a
large black spot on each side of the head; the quills of the large
feathers form in their sheaths; the scales of the feet are outlined in
a bluish tint; the bones, at first gelatinous, acquire firmness by
becoming incrusted with a small quantity of stony matter. From the
tenth day all the parts of the young chicken are well formed. The
little being, softly suspended in its hammock by means of the two
suspending cords that untwist little by little to give more room as it
grows, is bent over on itself, the head folded against the breast and
hidden under its wing. Note, my friends, that it is precisely this
attitude of deep sleep inside the egg that the hen assumes when she
wants to sleep. Crouched on her perch, she again folds her head on her
breast and tucks it under her wing, just as she did when she was a
little chicken in its shell.
“In the meantime the little bird keeps growing on the yellow and white
matter; matter which soaks and penetrates it and, vivified by the air,
becomes its blood and its flesh. One day it breaks the thin membrane
under the shell, and there it is more at ease with the increase of
space given it by the air-chamber. Now an attentive ear can distinguish
feeble peepings inside the shell; it is the seventeenth or eighteenth
day. A couple of days more, and the young chicken, summoning all its
strength, will apply itself to the arduous work of deliverance. A
pointed callosity, made expressly for the purpose, has formed on the
upper part of the tip-end of the beak. Here is the tool, the pick, for
opening its prison; a tool for that particular purpose and of very
short duration, which will disappear as soon as the shell is pierced.
With this provisional pick, the little chicken begins to hammer the
shell; perseveringly it pushes, strikes, scratches, until the stone
wall yields. For the most vigorous it takes several hours. Oh, joy! the
shell is broken; there is the young chicken’s little head, and all
yellow velvety down, and still wet with the moisture of the egg. The
mother comes to its aid and completes its deliverance; others, weaker
or less skilful, take twenty-four hours of painful effort to free
themselves. Some even exhaust themselves in the undertaking and perish
miserably in the egg without succeeding in breaking the shell.”
“Those are the very ones the mother ought to help,” said Jules.
“She would be careful not to, for fear of a worse accident than a
difficult birth. How could she direct her blows accurately enough not
to wound the tender little chicken just inside the shell? The slightest
false move would cause a wound, and at so tender an age any wound is
death. We ourselves, with all the dexterity and care possible, could
not, without danger, help the bird in distress; it can be tried as a
last resort, but the chance of success is very small. The young chicken
is the only one capable of carrying through this delicate deliverance
if strength does not fail it. The hen knows this wonderfully well, and
so does not interfere except to finish freeing the prisoner when half
out of its shell. Let us hope that things will turn out as we wish, and
that on the twenty-first day the whole family may be warmed under the
mother’s wings without mortal accident at the moment of hatching.
“From the instant of leaving the shell the young chickens already know
how to peck food and how to run around the mother who, clucking, leads
the way. They have besides a little fur of downy hair that clothes them
warmly. This development is not found in all birds; far from it.
Pigeons, for example, come naked from the egg and do not know how to
eat; the father and mother have to feed them by disgorging a mouthful
of food into their beaks. The young of the warbler, chaffinch,
goldfinch, tomtit, lark, in fact of nearly all the field birds, are
naked, very weak, at first blind, and completely incapable of feeding
themselves, even with the food just under their beaks. The parents,
with infinite tenderness, have for a number of days to bring it to them
and put it into their beaks.”
“That is a difference that has always struck me,” commented Jules.
“Little sparrows open their mouths wide to receive the food offered
them, but for a long time they do not know how to take it even if it is
put at the very end of their beak. On the contrary, little chickens
easily pick up from the ground for themselves the seeds and worms that
the mother digs up for them.”
“I will tell you, if you do not already know,” continued Uncle Paul,
“that the young of the duck, turkey, goose, and, among wild birds, the
partridge and quail, have the same precocity as those of the hen. They
are clothed with down on coming out of the egg, and know how to eat.
One of the causes of this difference in the way young birds act
immediately after hatching comes from the size of the egg. The chick is
formed wholly from the substances contained in the egg; the larger the
egg in proportion to the size of the animal, the stronger and more
developed the young. Therefore the kind with the largest eggs are
clothed at the time of hatching; they can run and know how to eat,
unaided. Where the eggs are relatively small the young are hatched
weak, naked, blind, and for a long time, motionless in their nest,
demand the mother’s beakful of food.
“The largest egg known is that of an enormous bird that formerly lived
in the island of Madagascar, and of which the species appears to-day to
have been completely destroyed. This bird is called the epyornis. It
was three or four meters tall and thus rivaled in stature a very
long-legged horse or, better still, the animal called a giraffe. Such
birds ought to lay monstrous eggs; such in fact they are; their length
is three decimeters and a half and their capacity nearly nine liters.”
“Nine liters!” exclaimed Emile. “Oh, what an egg! Our large vinegar jug
only holds ten liters. Certainly the young that come from that ought to
know how to run and to eat.”
“To equal in bulk the egg of the epyornis it would take one hundred and
forty-eight hen’s eggs.”
“I think they could make a famous omelet with only one of those eggs.”
“A fine large one could be made, too, with an ostrich-egg, which in
size represents nearly two dozen hen’s eggs. It need not be added that
young ostriches know how to run and to eat as soon as they come out of
the shell.
“Those are the largest eggs; now let us consider the smallest ones.
They are those of the humming-bird, a charming creature whose splendid
plumage would outshine the most brilliant costly metals, precious
stones, and jewels. There are some as small as our large wasps and that
certain spiders catch in their webs just as the spiders of our country
catch gnats. Their nest is a cup of cotton no bigger than half an
apricot. Judge then the size of the eggs. It would take three hundred
and forty to make one hen’s egg, and fifty thousand to make one laid by
the epyornis.”
“I imagine the little humming-birds in their nest must be all naked at
first and blind, taking their food from their mother’s beak.”
“From the smallness of the egg it could not be otherwise.”