I have Muscovy ducks. Over the past week to two weeks we have had 6 ducks/drakes/young die. They have had rapid weight loss, discolouration on their beaks and they can't walk or lift wings. What on earth can it be? When you pick them up they weigh like a few grams, lights as a feather.. And I'm not joking. It's like they don't have an inch of fat on them. We feed our ducks morning and night so it's not a not enough food problem. Anyone??