The Araucana, also known in the USA as a South American Rumpless, is a breed of chicken originating in Chile. The Araucana is often confused with other fowl, especially the Ameraucana and Easter Egger chickens, but has several unusual characteristics which distinguish it. They lay blue eggs, have feather tufts near their ears, and no tail (In North America). To comply with the North American standard they must have no tail and are rumpless.
The ancestors of the modern Araucana chicken were purportedly first bred by the Araucanian Indians of Chile — hence the name "Araucana." The Araucana is a hybrid of two South American breeds: the Collonca (a naturally blue-egg laying, rumpless, clean-faced chicken) and the Quetro (a pinkish-brown egg layer that is tailed and has ear-tufts). The Collonca male and female are very similar, with very few secondary sexual characteristics like comb, wattles or tail coverts to distinguish them.
The European equivalent of the North American show standard variety Araucana is what one comes across in South American villages. Quechua and Mapuche do not have tufts and resemble the Ameraucana.
The current worldwide Araucana Standard (except North America) indicates a medium- to large-sized chicken with a tail that lays bluish-green eggs. Specific features are feather ear tufts, muffs, and beards, with a very much reduced comb, a small feather crest and a complete absence of wattles. The current North American standard calls for a chicken that is rumpless (missing their last vertebrae and lacking a tail), possesses ear-tufts (feathers that grow out from near the birds' ears), and lays blue eggs. In the United States and Canada, muffs, beards, and tails are all disqualifications.
The Ameraucana should also lay blue eggs, but unlike the Araucana it has a tail and possesses muffs and a beard, which are quite different from the tufts of the Araucana, and no feather crest.
The Araucana's eggs are not more nutritious than eggs of other colors, nor do they have any negative health effects.
Read more about Araucana: Suggested Polynesian Origin, Recognized Breeds, Araucana, Ameraucana or Easter Egger?