We were recently given 12 chickens from a friend who was moving. When we picked them up I would say about 10 are missing tail feathers and feathers on their backs. I looked and did not see any lice or fleas. They were all kept together with about 10 others in a pretty small coop. What may cause this? Can it be passed to my other chickens? What will help the feathers grow back? Thanks in advanced!