I experienced something similar this morning as well. 1 week ago I got 7 new birds that were healthy and they have been well intergraded with my established flock. My black Australorp was just fine yesterday, running around, dust bathing, eating the works. I put them to "bed" at 8 last night and this morning I found her flat on her back but still warm at 6 this morning. There was no signs or symptoms and had me in a panic. I am a first time chicken farmer and I don't know what happened and am worried that this version of chicken SID's (Sudden Instant Death) will spread. I love my girls and I love to watch them and have them peck at me toes when I wear flip flops. They are so funny and great. I don't want to lose anymore. I now have a brief case of the sads with the loss of "Vicci" the black Australorp. (Yes I name my chickens, I bet you do too so hush!) I hope none of my others die and I hope this is just a one time thing. I wish every else luck with their flocks.
"Mom" of 2 Rhode Island Red (Tweedle Dee & Dum), 6 Americana's (1 "Carni" for carnivore cause I caught her eating an egg but she hasn't done it again since, 1 "Pigpen" cause she is constantly surround by a cloud of dust and the rest are called "fluffly cheeks"), 2 other lg black 'lorps "Gertie and Eunice", 1 Cornish "Gracie", 2 B&W Brahma's "Jemima and Jane", 1 white Cochin "Betty White" or "Midge" cause she is tiny, 1 sm black 'lorp "Ruby", 1 Buff Orpington "Balina" from wizard of Oz, 1 Turkin "Rosy" but my kids call her Ugly poor thing., 1 speckled Sussex "Sussey", and my favorite and Queen of the hens "Pepper" the Barred Rock.