I just went out to my coop to let my free rangers out for the day. My flock's rooster was laying down in the coop shacking and moving to the door slowly. He opened his mouth wide when he got to me and his head is low and wings are low. When I went to catch him he trying to run away but fell down and didn't get back up. I picked him up and examined him for injuries. There isn't any, and no infestations. Just shaking and weak. I have him in my house in a cage to keep him warm from the elements. Please help! What is this?