Why Have the Eggs of Birds so Many Colors?
The coloration of wild birds’ eggs is for protective purposes. The parent birds that incubate them are not always on the nest covering them, and at those times, the eggs are exposed to predators. Eggs often blend in with the colors around the nest so an enemy cannot spot them easily. The colors, speckles or spots on them are camouflage.
That explains why birds that nest in cavities often lay all white eggs. They can’t be seen even when the parent birds are not sitting on them. Ground nesters, such as plovers and terns, nearly always lay spotted, dull-colored eggs. These eggs are almost invisible against the ground on which they lie, while tree nesters often lay bluish or greenish 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. These are less visible in the uneven light in foliage. Eggs laid in dark holes, such as those of the woodpecker, are pure white, tucked out of sight; they have no need for camouflage.