I have 3 chickens: 1 Ameraucana, 1 Road Island Red, and 1 that looks like a Ancona. It's the Ancona look-like that is sick. This morning she was not in the coop area when I brought them food. She's always there and is the biggest eater and more aggressive. She was in a roosting section inside and did not come out even after setting down the 3 platters of food. About 30 seconds past and she came out only to shoot out a spray of poop and then proceed to peck out a small tail feather of the Red and eat it. She did the same thing the day before. This is the first time I witnessed this type of peck. She's very quite now, does not eat, and is mostly inside. I let them out in our backyard to roam around regularly. There's nothing there that's dangerous for them to eat. Yesterday she acted normal. I'm fairly new to this, since April, 2013. I acquired them through a friend. They are around 2-21/2 yrs. old. I have not had any problems with them until now. Should I wait until tonight or tomorrow to take action? If so, I have no idea what to do since I have no idea of what's wrong with her. Does anyone have any diagnosis and/or treatment? All responses are appreciated.