I had a 3 week old chick. a Sussex and I have never seen anything like this. I had spent many a day say in the garden just watching him and his 'crew' getting some fresh air on a lovely warm day. I started to get worried when he wasn't shaping up like that others. I thought maybe it was our big pig frizzle gobbling the food so I removed her. nope. so I removed him. nope. After further examination several times a day I noticed the breast bones becoming more pronounced and the wing spines very small and possibly brittle. I didn't want to try to bend one in case it caused pain. After lots of cuddles the little one was culled. there was no resistance, it seems that that was what he wanted. I hate culling birds... it makes me cry. the poor little thing. it does not seem to be infectious. none of the other birds have it. so the big question: what do you thing happened to him?