I have 1 roo in with 13 hens. Whenever he is mating with one of the younger girls, my older hen runs over to them and pecks the poor girl in the head! I've also recently noticed that at roost time she is last to go in the coop, after she has sent the others to bed. She just started doing this rounding up part, after her molt. Is this a dominance thing? Is it normal? Edited to add... she will be 2 in April and the girls she harasses will be a year in 1 - 4 months.