Ooh, that's great! I had no idea what to call it before, but now I was able to find a bit more information:
http://ameraucanaalliance.org/forum/index.php?topic=253.0
That's a thread on another site about Ameraucanas with feathers like OP's birds have, and they are calling it angel feathers, or boule, or bull neck. The thread has lots of pictures, and some speculation about the genes involved.
