Bird egg

Bird eggs are laid by the females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about seventeen (the grey partridge). Clutch size may vary latitudinally within a species. Some birds lay eggs even when the eggs have not been fertilized; it is not uncommon for pet owners to find their lone bird nesting on a clutch of infertile eggs, which are sometimes called wind-eggs.Classic oval bird egg (Spur-winged lapwing)Almost spherical bird egg (Senegal parrot)Long, 'elliptical' bird egg (Common murre) Bird eggs are laid by the females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about seventeen (the grey partridge). Clutch size may vary latitudinally within a species. Some birds lay eggs even when the eggs have not been fertilized; it is not uncommon for pet owners to find their lone bird nesting on a clutch of infertile eggs, which are sometimes called wind-eggs. Bird eggs are a special kind of dinosaur egg. The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines, produce colored eggs. The pigments biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting. Non-passerines typically have white eggs, except in some ground-nesting groups, such as the Charadriiformes, sandgrouse and nightjars, where camouflage is necessary, and some parasitic cuckoos, which lay eggs that often closely match the passerine host's egg. To varying degrees of success, host passerine species have combined speckles, blotches and other egg markings with visual pattern-recognition abilities to help them reject cuckoos’ counterfeit eggs. Most other passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors. However, the photographic markings on passerine eggs have been suggested to reduce brittleness by acting as a solid state lubricant. If insufficient calcium is available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil.