Bird Egg

the egg of a bird consisting of an ovum together with its protective envelopes: the yolk albumen, inner shell membrane, outer shell membrane and shell. Bands of thick protein, or chalazae, hold the yolk so that the side on which the germinal disk appears is turned upward. At one end of the egg the outer shell membrane is layered, forming an air cell.

The size of a bird egg varies from 8 × 13 mm (hummingbird) to 135 × 170 (ostrich), and the number of eggs per clutch from one (Procellariiformes, many guillemots, lyrebirds) to 20 or more (Galliformes). The shape varies from spherical to elongate-oval. The eggs may be spotted or monotone, and range from white or light blue to almost black. A laid egg (except for an unfertilized egg) usually already contains an embryo. Bird eggs, especially those of poultry, are used by man as food. In a number of countries, eggs are gathered in large numbers at sites of colonial nesting, for example, at bird rookeries.