I had seven 4 day old silver spangled hamburg chicks and 3 four day old serama chicks in the same brooder. I am now down to 3 and 3. The hamburgs have been mysteriously dropping like flies, one after another. They start to lay down, and when I go to check on them half an hour later, they are on their side twitching and peeping. I need some help, i've never seen this before. I know this doesn't have to do with temperature or a related brooder issue, my serama chicks are all fine.