I have a group of hens (RIR's and Leghorns) that recently started laying. I got a few other chicks that I've been raising in a pen in the large yard with the others. How do I know they're old/large enough to let out of their pen to join the others? They're about the same size as the Leghorns. I realized that I'm an adict. I can't go to the feed store without wanting another hen! Than you!