I have 5 hens. One of the hens (bardrock) head turned real yellow and was acting funny. She would not roost for 2 nights. She stopped eating and then I found her dead this morning. The other 4 hens are also acting funny. They are all piled on one another tonight in one of the egg boxes. They never do this. And they never sleep in the egg boxes. They are also not eating very well and are lethargic. Any ideas as to what is going on?