Not the best picture but it shows what I mean over a 4 day period. If you have your coturnix separated, its a lot easier to notice. Each bird lays an identifiable egg. This pic is from a handful I had separated for a buyer. There's little dark bottom, marbled, moustache pattern, and the speckler. Some birds lay a much less speckled or plain egg, but certain features are easy to pick out. I have other birds that are prone to laying double yolkers or nearly white eggs.