I started with 10 chickens-red sex links. Yesterday I woke up to check on my flock and 4 chickens were dead on the coop floor. Almost looked like they fell off their roost and died. Then I found one alive (now dead) laying in the hay but breathing shallow. She died 2 hours later. The first four had been dead a few hours and did have small amounts of mucus/snot coming out of their nostrils, the last one did not. From what I saw, it did not look like predators. They looked healthy (besides the small amount of mucus) with all feathers intact, no blood, no struggle. I added some electrolytes to the remaining chickens water and so far, no more have died. The crazy thing about this is, 3 months ago, I had 2 chickens do the same thing - AND the same night my neighbor had 2 chickens die the same way. My chickens have access to the outdoors to free range but my neighbors chickens are totally fenced in. We called the fish and game dept. and they don't seem too concerned but it seems really odd to me, 50% of my flock dying in one night. Does anyone have any idea of what could have caused this? Thanks!