Hi...I also raise Ameraucanas and have noticed that many of the chicks in the black variety often die within the first 2 weeks...its a failure to thrive kind of deal...I have one little lav right now who I am sure would have died if i hadnt given it some tlc as in a smaller group and kept in the house brooder longer...I also have had a few black Ameraucanas the same way and after about 6 weeks they take off and all are the same size after a couple of months maybe some genetics just make them more susceptible to chick mortality....do you cross yours into your black lines as i believe thats what i will do as i have some great blacks with hi hatchability and live chick rates...I also have a trio of split lavs that were hatched out under a broodie and seem to be hardier birds....have you had much problems with blindness in the lavs... me thinks a variety not for the faint of heart...