My 1 1/2 year old Buff Orpington, Heidi, died today. I let her out this morning, and nothing seemed amiss. She has been laying well, and there were no apparent problems. There were no obvious injuries, etc. She was just lying in a little dust bath, flopped over. I have several questions about this situation. First, I'm sure chickens die all the time for no clear reason, but do I need to be worried about infectious disease? My little flock of 4 urban hens has a run which is covered with chicken wire, so they are exposed to wild birds. Next, this leaves 3 hens, one of whom has seemed a little poorly recently. She is coming out of her moult, during which she was traumatized, but not obviously injured, by being carried around the backyard by my large dog, and has not ever gotten quite back to herself. Here's the worry: whether or not she makes it, my little flock is depleted, and I'm worried that they will have more trouble staying warm this winter. I have read about all the difficulties of introducing new hens into the flock, and I don't know if this is a good time of year to do that. I am allowed a maximum of 6 hens, and have had plenty of eggs with the four, so I was thinking of adding two. If I do, should I do it now, and how old should they be? Similar in age to the present flock, or can they be this year's pullets? Any advice as to what the best thing to do is at this point?