We currently have 3 chickens outside in our coop and run, 2 Barred Rocks that are ~12 weeks old and a Buff Orpington that is ~20 weeks old. They spend the day running around a fenced off part of our backyard and then are locked in a 4x6 pen overnight. Last night, when I went to shut them up, I noticed that the two Barred Rocks were on their perch, but the Orpington was nowhere to be found. I looked around the pen and eventually found her under the coop, lying down. She seemed alright but she was really quiet, which I figured was probably a sign that she was going broody (we'd been waiting weeks for that first egg from her!). I went upstairs and told my wife that we might have our first egg in the morning! Unfortunately, we woke up this morning to find a dead chicken instead of a fresh egg. The Orpington was still on the floor of the coop, right where I'd put her in last night. And now I'm left scratching my head, because right until late last night she was running around as healthy as ever. No signs of illness, injury, disease -- anything. We've had her for about 6-7 weeks, and she'd spent a full month in quarantine. There was literally nothing this time yesterday to suggest that anything was wrong with her, so I'm left clueless. Does anyone have any experience with things like this happening or any ideas why she bought the big coop in the sky? Should we be worried about the Barred Rocks and/or doing anything preemptive to keep them safe?