I have 24 ducks...cayugas, runners, mallards, muskovies, pekins, calls and swedish. Some of them look like they've been losing weight! We've had many very humid days in the last couple of weeks so could that be contributing to it? I don't think anyone has lost their appetite, and they have plenty of water available. Their poop doesn't look any different either and their energy levels seem to be the same except when it's really hot they of course will lay in the shade. Their weight loss isn't drastic, they just look a little bit thinner, and not all of them.