Raptor Propagation: The Egg

The egg is a complex and marvelously efficient self-contained universe. In this post, I’d like to share with you the basic components of eggs and how they function in protecting and nurturing the embryo.

The avian egg contains three membranes that support the life and development of the embryo:

The amnion is an inner layer of cells that surrounds the embryo and secretes the amniotic fluid in which the embryo floats. The amnion both protects the embryo and prevents it from drying out.

The chorion surrounds the embryonic structures and serves as a protective membrane.

The allantois (or allantoic sac) grows larger as the embryo develops, eventually fusing with the chorion. The chorioallantois works to permit respiration and excretion. It is important in storing the chick’s nitrogenous waste, or uric acid.

The four primary components of an avian egg (from the inside out) are:

The yolk, which feeds the chick during and after incubation. The avian yolk is between 21% - 36% lipids and 16% - 22% proteins (the rest is water), and is suspended in the center of the egg by the chalaze, which are strands of protein fibers. The yolk also contains antibodies from the mother to protect the chick from infection.

The albumen is the chick’s water supply as well as a buffer that helps protect the embryo from jostling or sudden changes in temperature.

Shell membranes (inner and outer) are attached to the shell and help protect the egg from bacterial invasion as well as preventing rapid evaporation of moisture from the egg.

Finally, the shell is the embryo’s outermost protection. Eggshells contain thousands of pores to permit gas exchange. The color of an egg shell is determined by pigments in the mother’s uterine wall.

When the egg is laid, it begins to cool and the inside contracts, forming an air sac. Observation of this air sac allows us to monitor the progress of incubation and indicates when the egg is near hatch. More on that in my next propagation post when I’ll answer the question: She laid an egg, now what?

And here is another video of a barn owl chick. He’s awfully cute at three weeks old!


Two sources were used as a reference in preparing this post:
http://www.msstate.edu/dept/poultry/avianemb.htm
http://people.eku.edu/ritchisong/avianreproduction.html