I have 4 mandarin ducks, 2 males and 2 females. I bought them in May last year, when they are still young. I am keeping them in a pen in the barn with metal mesh overhead so that they don't fly away. I give them duck grower pellet and a container of water. They look happy and active even in the coldest of winter. Today at two o'clock I was adding water to their container, they all look fine to me. Then at 5 o'clock, I found one female dead just beside the water container, lying on her back, neck stretching backward, she must have been dead for sometime because her body is already hard. She's a little wet at one side. I feel so sad, I don't know what caused her death, no wound, no discharge, no blood, her eyes are still open. no obvious sign of disease. If is some sort of disease, would the remaining ones get it too? Mandarin ducks are highly admired birds in my native country, they are a symbol of love. And they are beautiful birds, I become attached to them shortly after I had them, I just feel so sad. recently I have not introduced any new birds to our barn, I have not been to other people's house. And the barn is closed, not other birds can get in. They live in a closed pen and no others get inside, I just don't know why.