Last night when i was checking on everybody, one of my roosters rattles when he breathes. There is no mucous bubbles, his eyes are clear, he is eating and acting fine. Could it be because of the changing temps? One night it gets to -20 then the next day its 27 degrees F. There is a heat lamp in there but it only keeps the temp 5 degrees above what it is outside on the cold side of the coop. I have the heat lamp pointed over top of the perch. Everyone else is fine. I cant afford to bring him to the vet right now. I have access to tetracycline and sulmet or i can get what is recommended at TSC. It has to be safe for ducks since 3 share the coop.