ok, I'm at a loss.
I will tell you I believe strongly in sunshine and fresh air as absolutely essential for the health of any chicken. I've asked a couple of friends to chime in. saladin
It could be any number of causes. You'll have to give more information like how old they are, what are you feeding, and any other signs.
For example, molasses will make them do this, but so will some illness. As you can see those are very different causes. saladin