I know this is kinda random because nothing was said about a fungus or bacteria in a while, but it can't be either of those because what are the chances that the beaks would only fall off at night? I mean why at night when there are so many predators and stuff out. If it was bacteria I think it would happen in the daylight too, unless by some stretch there is some weird thing that only happens to the beaks and only when they are sleeping. I'm sorry about your birds
