Update: the chick died. This morning when my husband went to let out the chickens, he found that one of our four-week-old Buff Orpington chicks had a bloody flayed back! The chicks had been closed up by themselves in a separate coop with their "mother," a Silkie cross, and are also within an electric poultry netting pasture patrolled by a guard dog. After we took pictures, I sprayed her liberally with BluKote and put her in a brooder with some 2.5 week old ducklings so that the adult chickens in that pasture wouldn't pick on her. She seems to be in pain and in shock and I am monitoring her closely. I know that this had to have happened sometime during the night last night because: 1. When I did a head count last night while closing everyone up, the chicks were all fine, and 2. The blood is too fresh to have happened yesterday during the day. Here's pics of their house. It's a Rubbermaid-type shed with hardware cloth windows. The Buff Orpington chicks and Silkie Mama are the only ones in it at night. Everyone else is in a separate coop. So do you think that Silkie Mama did this? Or that we have rats? Or something else? The other odd thing I wanted to mention is that a few weeks ago, I attempted to graft two Lavender Orpington chicks onto Silkie Mama for her to raise with her Buff chicks. I know it's risky but I've had good luck with some mamas so I wanted to give Silkie Mama a try. They were about two weeks older than her Buff chicks. I carefully monitored the Lavender chicks with her during the day and while she seemed slightly skeptical at first, she completely ignored them the rest of the day. (Not violent, just skeptical.) The next morning, both Lavender Orpington chicks had wounds just like this chick does. We assumed that Silkie Mama took offense to them being in the coop with her and her chicks at night and beat the crap out of them so I of course immediately removed them. (They are doing just fine, btw.) But if she did indeed injure those Lavender chicks, why would she hurt her own baby? She's been a great mom to her Buff chicks.