The sexers at the hatcheries have been doing it for ages... there is a very rough (for the chick) process of squeezing their belly just right to make them poop and then squeezing again to look in thier vent to look and see if they have a "bump" or not. Not sure which is the female or male. And even these guys only have a 95 percent accuracy rate. This can only be done on day olds to be accurate and has to be done by an expert. By the time we get them at a few days old or older, it is too late. But some breeds have "sex links" which give them defining characteristics at birth to tell gender. So I guess it depends on which breeds you have.