What’s in a bird egg?
Interestingly, all bird eggs have the same basic components and physiology. The exterior part of a bird egg is comprised of three layers: the cuticle, which is the soft, thin outer part surrounding the shell, acts as a protective barrier, preventing water evaporation and infection from penetrating the surface; the hardened shell, which is made primarily of calcium carbonate, is a semi-permeable layer, allowing air and moisture to pass through its pores; the final part is two inner layers, which are essential protein layers.
Within the egg, there are two key parts: the albumen and the yolk. The albumen, which is 90% water, functions to protect the yolk and provides added nutrition to the embryo. The yolk, of course, is there as a primary source of food for the development of the embryo. It is considerably rich in protein; in fact, the darker yellow the yolk is, the more protein is contained within it.
Interestingly, the size of a bird’s egg is relative to the size of its yolk. And, of course, the size of the yolk is relative to the size of the species.
*This chart shows the correlation between the size of common garden birds the size of their eggs.