Abstract
I had just asked an old-time aviculturist, Birdie Whitelaw, about his remarkable success with artificial incubation. It seemed that every fertile egg he set in his incubator hatched into a healthy, vigorous chick.
Birdie opened his toothless mouth in a sly smile and said, "I just take an egg, heat it up for a spell, and out comes a little birdie:'
If I had only known that fifteen years ago, I may not have wasted all that time studying incubation. I must remember, though, that artificial incubation can be described as being nine parts science and one part magic and though I have met a few people, like Birdie, who I consider masters in the art of artificial incubation (and I revere them as alchemists of the highest order), you don't have to know magic to hatch an egg in an incubator. Incubation is still nine parts science and with a little knowledge of how an incubator works, how an egg develops and hatches, and a bit of practical common sense, anyone can develop satisfactory artificial incubation techniques.
The Egg
In mammals, when a female ovulates, a tiny follicle ruptures on the ovary releasing a one-celled gamete called an egg cell. If fertilized, it attaches itself to the lining of the female's uterus and draws its nourishment from the systemic nutrients of the female. Bird ovulation is very different. When an ovarian follicle ruptures in a hen, an entire egg yolk is released. On the surface of the yolk is a tiny gametic.spot called the germinal disk, blastod1sk, or germ spot. This light-colored dot is visible on all egg yolks, fertile or infertile.
The yolk is then captu~ed by the infundibulum of the hens oviduct. Here is where fertilization takes place; the sperm cell unites with the gametic portion of the egg on the germ spot. Quickly, the vitelline membrane is laid down around the yolk, wrapping the developing zygote in the first of several protective coverings. As the egg passes through the hen's oviduct the albumen, or egg white, is wrapped around the yolk and this is all covered by the inner shell membrane, the outer shell membrane and the egg shell. Penetrating the shell are millions of tiny pores. These pores allow oxygen to enter the egg and carbon dioxide and other wastes to exit the egg. Covering the shell is a waxy cuticle, or "bloom'.' This "bloom" prevents a too rapid loss by evaporation of moisture from the egg.
Finally the egg is laid. The egg-laying process takes about twenty-four hours from release of the yolk from the ovary to depositing the egg in the nest. During that twenty-four hour period the embryo is exposed to the body heat of the hen and the zygote begins to develop.
When the egg is laid, no longer kept warm by the hen's body heat, it cools to room temperature. This gradual cooling arrests the development of the embryo at a primitive, microscopic stage and causes the egg contents to contract. As they cool and contract, the inner shell membrane pulls away from the outer shell membrane, forming the air cell.
When the egg is reheated during incubation the embryo develops quickly. In the first few days a heart forms and blood vessels surround the yolk, pulling nutrients from the yolk and albumen and delivering them to the embryo. The eyes begin to develop, limb buds are formed and the chick begins to move on its own. This first one-third of incubation is very important to the developing embryo; extreme variations in temperature and/or humidity or inadequate turning of the egg can cause the death of the chick.
About two-thirds through incubation, the embryo, now a chick, has developed down feathers (if it hatches with down) and is very active in the shell, responding to light, vibration, and loud noises. During the last third of incubation the chick grows to completely fill the shell and positions itself, head under right wing, for the hatch.
The Incubator
There are two main types of incubators; the forced-air incubator and the still-air incubator. The forced-air incubator has a continuously-running fan mounted inside the incubator to keep the warm air circulating around the eggs. Because the still-air machine does not have a fan, the management of it is different than the forced-air incubator. These differences will be pointed out, where appropriate, throughout the rest of this article.
All incubators have at least three parts in common. They are: (1) a cabinet, (2) a heat source, and (3) a source of humidity. Beyond that there are as many variations as there are people with better ideas. I met a man who had perfectly acceptable hatches using a plastic garbage can, a light bulb and a pan of water. At the other end of the spectrum, I know a man whose incubator is equipped with two thermostats (in case one fails), an alarm system that will also page him at his house in case there is an accident, spot lights and stereo speakers mounted inside the cabinet. (The lights and sound system are used to stimulate and exercise the developing chick - like teaching calculus to your child before it is born.) And this man has good hatches, too. As you develop incubation skills and begin to feel comfortable with the basics, your machine may undergo some modifications, but my advice to the beginner is to buy a machine and follow the manufacturer's recommendations.
The cabinet is simply the container that traps the heat and humidity around the incubating eggs. It can be made of wood or plastic but should be insulated well enough that your heat source doesn't have to work all the time. There should be at least two adjustable vent openings and a way to read the temperature and humidity without opening the machine. The heat source can be a light bulb, but a radiant heat element is preferable as too much light in the incubator may damage the developing embryo. Humidity is usually supplied by means of a pan of water in the bottom of the machine. The humidity can be increased or decreased by changing the surface area of the water to encourage or discourage evaporation. Large, shallow pans provide the greatest surface area of water and, therefore, the highest humidity. Smaller, deeper pans decrease the surface area of the water and, as a result, the humidity.