Need some help and advice. We have 16 chickens and a Roo. 10 chickens were inherited from my parents, 6 are almost 4 months old. One of the 4 month olds is not staying on its feet for long periods of time. its head/neck is pulled in and it keeps falling over/laying around. Any ideas on what is happening? Anything I should do? All of the other chickens, new and old are doing fine.