Bird eggs are an important step in the process of reproduction of birds. Instead of developing fertilized ova internally like mammals do, birds lay eggs which consist of an ovum protected by a hard outer shell. If the ovum has been fertilized, it will develop into an embryo which will eventually turn into a chick which will hatch from the egg once it has fully matured. In addition to being important for birds, bird eggs are also viewed as a useful food source by many animals, especially humans.
There are three major parts to bird eggs: the yolk, the white, and the shell. The yolk or vitellus provides a source of nutrition to the chick as it develops. The white or albumen surrounds the yolk, shrinking over time to give the chick room to grow, while the shell protects the developing embryo until it is ready to hatch out.
Naturally, birds do not keep a store of eggs ready to go inside their bodies, as this would be rather uncomfortable and impractical. Instead, birds periodically deposit layers of calcium and other materials around their ova, forming an egg which is pushed out when the bird is ready to lay. When laid, eggs can be oval to round in shape, and they vary widely in size and color.
As a general rule, the smaller the bird, the smaller the egg, because the egg needs to be pushed out of the body, so there are certain size limitations involved. Egg colors can include brown, blue, green, and white, with some birds producing speckled or flecked eggs. Spotted bird eggs are sometimes collected by artists and nature enthusiasts as they are visually interesting.
In the case of fertilized eggs, incubation is usually required for an embryo to develop. Incubation is done by the parent birds, who sit on the egg to warm it as it develops. It is also possible to use an artificial incubator to incubate eggs, a common practice in livestock production. Unfertilized eggs will fail to develop and they will ultimately rot.
Every part of the egg is edible, although humans tend to avoid the eggshell. Eggs are high in protein and other nutrients, since the rich yolks are designed to provide nourishment to baby birds as they develop. Eggs can be prepared and used in a wide variety of ways, with chicken, duck, and goose eggs being most commonly consumed by humans.
In addition to being a food source, bird eggs can also be used by artists. Some artists like to blow eggs, carefully punching holes in the shell and forcing the contents of the egg out. The hollow eggshell can be painted, carved, or otherwise decorated to create a work of delicate art.