I read this article in " Backyard Poultry"... Occasionally an aged or diseased hen will take on a cock-like behavior. Hens have two ovaries, but only the left one produces eggs, while the right one remains undeveloped. If the left becomes inactive, then the right ovary is stimulated into functional activity, resulting in the hen getting a dose of male hormone. Then she could start crowing. Just thought this was interesting.