The Egg Assembly Line

By Scott Fitzpatrick on Friday, June 8, 2007.

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A lot goes into making an egg - and it's all intended to keep the developing chick safe until it's ready to hatch.

Hi, this is Scott Fitzpatrick from New Hampshire Audubon, bringing you Something Wild.

Have you ever considered the egg? A bird's egg is a perfect, self-contained life support system. It provides everything the developing chick inside needs to survive except warmth and oxygen. Eggs are formed one step at a time inside the female bird, production-line style.

The ovum, or reproductive portion of the egg, is held in the bird's ovary for several days as the yolk forms. It contains all the nutrients that the developing chick needs, and when it's ready the yolk and ovum travel into the oviduct. Fertilization, if it is to take place, happens here.

Next, the fertilized ovum travels down the reproductive tract to where the egg white, or albumin, is added. This jelly-like substance provides water and acts as a shock absorber for the chick.

Further down the line, two thin, soft membranes are added around the ovum and albumin. They hold the mass together and give it shape. The ovum is beginning to resemble an egg.

Next, the soft egg moves into the shell gland. It remains here for 20 hours or so, as the hard shell is secreted in layers. It is made of calcium carbonate and a little protein. Any coloration or speckles are added as the egg leaves the shell gland. Before that, all eggs are white.

Once the shell is thick and hardened, it gets a last coat of protein to protect the interior from bacteria. And then the bird lays her fully-formed egg.

Eggshells contain tiny holes. Once the egg has been laid, these openings allow oxygen to reach the developing chick and transport waste gases outside. The parents just need to keep the eggs safe and warm until the hungry baby bird hatches.

For Something Wild, Iâ€™m Scott Fitzpatrick.

Something Wild is a joint production of New Hampshire Audubon, New Hampshire Public Radio, and the Society for the Protection of New Hampshire Forests.