"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." - (en.wikipedia.org 26.08.2021)
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