I have 9 hens who just turned a year old. One barred Rock has started pinning another to the ground and pecking her head so hard she has pulled out half the feathers and made her bloody a few times. Today, I witnessed a RIR HEN doing this: What in the heck are my chickens doing? All of them came over and started pecking the bottom one's head in the 30 seconds this happened. Thanks in advance.