I'm so glad I found this thread! We lost one of ours this way last night. Everything seemed fine, she was the dominant chicken, then when my husband went out to put the girls up, she was dead in the middle of the run. No sign of any external stress (predators, etc.) Just dead. I'm sad because that is 3 out of 4 of our first set we've lost. The other two were predator losses. This one was my favorite of the 4, too. Luckily, I have 2 more "little" girls that are ready to go out with the big girl. It was comically tragic. Everyone is afraid of everyone. The big one isn't being aggressive, but anytime she goes near the 2 new ones they run away and anytime they walk by her she flips out and moves. We had tried integration a few weeks ago and Hazel, the one that just died, was enforcing pecking order so I think that is why the littles are wary. I'm sorry that so many of you have had to deal with these unexplained losses. At the same time, it made me worry a lot less about mine.