Hi, I have two hens that are probably a year and a half, and one that was born this past spring. The older ones are also a different breed (black sex-link). I've noticed at least one of the sexlinks are picking on the barred rock, who is a little smaller than the two. I first noticed this when I got the hens the other day and held them down to clip their feathers. I did the black ones, and then when I got the barred rock, a funny thing happened. Noticing her in her vulnerable state, one of the sexlinks ran over and gave a nasty pick to the barred rock right in my hands. Anyway, this got me wondering about pecking order. I know it is normal for the hens to establish their hierarchy, but I am curious if it is ever unhealthy to put certain chickens together based on size or age. I am wondering if I am to get some pullets or chicks and raise them up, at what age or size can I put them with the older more established hens and not worry too much about them picking on them in an unhealthy way. Thanks!