Bird egg

Bird eggs are laid by the females and range in quantity from one (as in condors) to up to seventeen (the grey partridge).

[3] However, the photographic markings on passerine eggs have been suggested to reduce brittleness by acting as a solid state lubricant.

[4] If insufficient calcium is available in the local soil, the egg shell may be thin, especially in a circle around the broad end.

The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting the gene responsible for pigmentation is on the female-specific W chromosome (female birds are WZ, males are ZZ).

However, this theory has been refuted by studies of egg shell formation in a number of bird species using techniques such as X-ray photography[14][15] which have demonstrated that egg shape is determined in the oviduct isthmus (before shell calcification) with the pointed end caudal (furthest down the oviduct).

[18] This evolutionary trait results in kiwi chicks that can emerge from the nest days after hatching, ready to start foraging for food.

For example, the principal predators of the black oystercatcher's eggs include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes.

The stoat (Mustela erminea) and long-tailed weasel (Neogale frenata) steal ducks' eggs.

Ostrich eggs are vulnerable to many predators ranging from mongooses and Egyptian vultures, to hyenas.

[citation needed] Brood parasitism occurs in birds when one species lays its eggs in the nest of another.