Sexing Araucana chicks.....

Are lav araucana chicks difficult to sex or are there any tell tale signs I should look for with this breed? I have 3 all aged 4 weeks. One looks a bit runty compared to the others but that's all I can pick up on at the moment.

they can be very difficult to tell, I had one white one from a breeder and at 6 months she became a he started to crow and mount the others - and was very fertile 

odd looks  , I think they are stunning (although I prefer the black version  ).