I would agree with the 'hot' reason... when my dotte (BLRW) gets hot, she's got lazy wing carriage...smart and fast way to cool off (-;Sometimes it is because the birds are hot. I had thought split wing was caused by a missing feather, but one of my Barred Rocks has split wing on one side only. He has all the correct number of feathers, but wing looks like photo posted above. I took him to a show just because I wanted a professional opinion on him and sure enough, the judge said split wing.