Birds' eggs are conveniently classified as marked or unmarked, according to the ground color. Birds which lay their eggs in holes in trees or in the ground almost always have white, unspotted eggs. Birds which build in trees generally have blue or greenish eggs, either spotted or unspotted, while birds that build in bushes, near the ground, are likely to lay speckled eggs.
Publications
- Thomas Mayo Brewer, (1814-80), an American ornithologist, wrote most of the biographical sketches in the History of North American Birds, by Baird, Brewer, and Ridgway (1874-84). He has been called "the father of American oölogy". He wrote North American Oölogy which was partially-published in 1857.
- T. G. Gentry, Nests and Eggs of the Birds of the United States, (Philadelphia, 1885).
- Oliver Davie, Nests and Eggs of North American Birds, (fifth edition, Columbus, 1898).
- William Chapman Hewitson, Illustrations of Eggs of British Birds, (third edition, London, 1856).
- Alfred Newton, Dictionary of Birds, (New York, 1893-96).