What Happens When Eggs Aren't Incubated?

Oology is the study of bird eggs, and researchers are called oologists. The study of eggs also intrigued Aristotle, who described almost 140 species of birds. According to researcher Michael Walters, Aristotle wrote that the "length of incubation varied with the size of the bird." Those observations remained unchallenged for 2,000 years. In 1953, American ornithologist Margaret Morse Nice traced the historical research to discover scientists had merely copied Aristotle's conclusions instead of testing them.

Avian eggs develop in the female bird over a 24-hour period. An ovum (egg yolk) is released and covered with albumen (egg white), and then receives a hard shell covering; and, depending on the avian species, pigmentation. The egg then is laid through a bird's cloaca, which is the opening for elimination and fertilization. Ornithologists refer to the moment of possible fertilization as the cloacal kiss. Kissed or not, the female still lays eggs. If the eggs are taken from the nest, the female lays more, which is why you have chicken eggs for breakfast.

Birds incubate infertile or fertile eggs. Infertile eggs collapse due to lack of embryo growth. Fertile embryos develop inside eggs warmed by adults. Hens will lay over 1 to 2 days, after which full-time incubation begins. Delayed incubation slows development, but doesn't harm embryos. Once incubation starts, hens will not leave the eggs. Hens will get off the eggs to roll them; scientists believe this encourages embryo development. Disrupting incubation at this point threatens embryo growth and chick survival. Incidents harmful to complete incubation include hens becoming prey; dying from diseases, like West Nile virus; or nests blowing from trees. Any egg that is not incubated at all will not hatch.

Egg incubation became an important experimental component at the Central Veterinary Research Laboratory in Dubai, United Arab Emirates. Researchers wanted to boost reproduction rates of the over-hunted houbara bustard to repopulate its habitats in the Arabian peninsula, Northern Africa and in parts of Central Asia. To that end, researchers devised a way to grow bustard chicks inside chicken eggs. To assure hatching success, eggs were incubated in temperature-controlled environments.