When I went down to my chicken coop to put my chickens up, I noticed one was not acting right. It repeatedly ruffled its feathers, and made a trilling noise, unlike any other noise I have ever heard from a chicken. It almost sounded like it was having a hard time getting air out. This morning, I found it in the coop on its side, dead. Their were no external parasites, other than flies, and no mites or ticks. I really need to know what this is, so that I can save my other hens.