On the right is an Araucana hen, with ear tufts. Corallina Breuer took these photos, which are also in "How to Raise Chickens."
Ann Charles of Sky Blue Egg in Mena, Arkansas, http://www.skyblueegg.com/, tells me that she can separate the Araucana cockerels from the pullets by four and a half to five weeks of age "with about 95% accuracy. The pullets combs will be yellow at this age and the cockerels will be pink. The cockerels are usually the bigger more vigorous chicks at five weeks."
Araucanas are rumpless and lay blue eggs. They are a breed unique to South America, first mentioned in North America in 1914 and introduced via illustration in The National Geographic Magazine's special issue on poultry in April 1927.
Ameraucanas are a production breed developed in the 1970s to incorporate desirable Araucana traits with more practical strengths. They lay either blue or khaki green eggs. The khaki green color results from the blue gene combining with a brown egg gene.
Various breedings have brought the delightful coloration into other chickens with less distinct blood lines. Any chickens that lay blue or green eggs are called Easter Egg chickens.
All other ideas on sexing young Ameraucanas and Araucanas gratefully received!