My 9 week old chickens are losing their feathers on their lower back above their tails. We lost our very first chicken yesterday. Came home and found one of my Ameraucana's dead in the coop, the other chickens in the flock we pecking at it. Then to find out we have 4 and possibly a few more with feathers gone above their tails. Could this feather loss be a result of pecking from other chcikens or could they have mites? This is our first time raising chickens and we could really use some advice.