The difference in the colours of bird egg shells has to do with genetics, which is why some chicken eggs are white and others are brown. There are no nutritional differences between eggs of different colours, according to NPR. Chickens with white feathers will lay white eggs as opposed to chickens with brown feathers, which lay brown eggs. Similarly genetics determines the colour of the eggs that other birds lay.
Pigeons also lay white eggs, usually two at a time. It takes 18 days for the eggs to hatch. Male and female pigeons take turns sitting on the eggs to keep them warm during that time. The eggs are kept at a temperature of 37.5 to 38.0 degrees Celsius, according to Farming Friends. Both the male and female produce a special milk they feed to the baby pigeon after it is hatched.
Bluebirds lay white eggs, though blue and pink eggs are more common. Only about 4 per cent of bluebirds lay white eggs, according to Sialis. There are three species of bluebirds: Eastern, Mountain and Western. The population of bluebirds has decreased due to an increase in the starling and sparrow populations, which compete with them for food, according to The North American Bluebird Society. Bluebirds usually lay four to five eggs at a time.
Wren eggs are white with brown speckles. Wrens are usually covered in grey and white feathers. A Wren will lay five to six eggs, which take up to 15 days to hatch, according to Wild Bird Watching. The young birds will remain in the nest for three weeks before leaving. Wrens are very aggressive birds and will destroy other nearby nests and eggs. These birds will nest in birdhouses and are easily attracted to them, according to Wild Bird Watching.
Tree Swallows lay pure white eggs. These eggs are much smaller and have a pointed top, according to Sialis. Swallows lay four to six eggs. These eggs will hatch in 13 to 16 days, according to Chipperwood's Bird Observatory. Similar to bluebirds, these birds have dark brown and blue feathers. Young swallows are born blind and are fed by their parents for three weeks before they leave the nest.