We are down to only 4 out the 7 chickens that we started with. They were 5 weeks old two of them were/are plymouth black rock and five of them are/were orpingtons. We don't the entire area covered and so we think a hawk is swooping down and grabbing them.
Our solutions: add bird netting or some sort of cover and get more chickens hopefully older and hope they don't kill each other dominating the pecking order.