Rooster and older Hen turning mean

[Coyoteowl]

Last year a Bobcat ate my entire flock except for one hen. I have raised a new flock and slowly let the older hen get used to the new chicks. She stepped up and acted like a mom and everyone was happy. I ended up with 4 roosters and Re-homed 3 keeping the smaller one since he was the right size for my hens. Flash forward 5 months...…. I'm getting eggs from All the hens now and everything has been great, one big happy flock. In the last 2 weeks I've caught the older hen attacking one of the younger birds. She literally smashes the hen to the ground and pecks her head. Yesterday I caught the Rooster and older hen brutalizing the younger bird. I cant tell if the younger bird is always the same one since I have 5 ISA Browns that look exactly the same. I have looked over the flock for any signs of injury or sickness, nothing. How do I get the older hen to quit being so mean?

 

[Sc_chickengirl]

Last year a Bobcat ate my entire flock except for one hen. I have raised a new flock and slowly let the older hen get used to the new chicks. She stepped up and acted like a mom and everyone was happy. I ended up with 4 roosters and Re-homed 3 keeping the smaller one since he was the right size for my hens. Flash forward 5 months...…. I'm getting eggs from All the hens now and everything has been great, one big happy flock. In the last 2 weeks I've caught the older hen attacking one of the younger birds. She literally smashes the hen to the ground and pecks her head. Yesterday I caught the Rooster and older hen brutalizing the younger bird. I cant tell if the younger bird is always the same one since I have 5 ISA Browns that look exactly the same. I have looked over the flock for any signs of injury or sickness, nothing. How do I get the older hen to quit being so mean?

The easiest thing would be to just separate them but...

 

[DobieLover]

Are they free ranging or contained in a pen/run?
If they are contained, how much space do they have and what is in the space?
Chickens like structure that they can hide behind and perch on. Lots of clutter is great for chickens.
If ensuring they have enough space and lots of things to do in the space does not resolve the issue consider pinless peepers.