I have 5 young Marans (between 2 1/2 and 4 months) in a really huge pen for 5 (8 x 20). It is a tractor that gets moved every 2 weeks. I was really excited to get the tractor going because I wanted them to get a new healthy spot of grass rather than living on a build up of whatever!! I got these chicks in a batch, they are pretty wild but I have been able to get them to start eating out my hand lately. I also noticed that although none of them seem ill, they do sneeze more than my other chickens, with whom they have never been mixed. I've had them about 6 weeks by now and all was OK. On Wednesday one was not looking well and she let me walk over an pick her up which was really weird but she still did eat. Because of the sneezing I immediately thought respiratory so I put electrolytes vinegar and a spot of sugar in the water. Last night she was looking decidedly worse so I brought her inside. Her symptoms were Lethargic, Depressed, Feathers ruffled, She seemed to be having difficulty breathing and was wheezing just a little bit but it was not loud. There was no snuffly mucus noise. She also had diarrhea that showed up really late in the illness. A couple of hours later she keeled over on her side, flopped around a bit and died .... I am wondering if this was not respiratory at all, but was hoping that maybe someone out there with more experience can see anything more obvious that I missed. I'm pretty worried about the rest of them out there now, although so far they look OK.