One of my three week coturnix has a swelling on his head behind his eye. It is not oozing or anything like that and he doesn't appear to be in pain but it impairs his vision on that side a bit. None of the 16 other birds in his brooder have it. I figure best case it's an air bubble, worst case it's something contagious that will kill all my birds. I'm hoping you guys could help me figure out what it is.