I have heard of that since the very beginning of my chicken raising experiences. An old lady from this town was allowed to pick out her own chicks at the feed store from the straight run brooder and did it with 100% accuracy. I tried learning to vent sex and killed one of my pullets back in May, so I look real quick, but I am not certain. I separated my chicks about 3 days ago. The ones I knew were roos, did fight. The ones I knew were pullets didn't fight. The others, I did the 'test' on and separated according to how they acted and hopefully I am mostly right.
I would have wanted more roosters because I incubated to fill my freezer and plan on selling the pullets.
I would have wanted more roosters because I incubated to fill my freezer and plan on selling the pullets.