Our 10 Welsh Harlequin ducklings came in from McMurray Hatchery yesterday morning. They are our first ducks. We have them in a cardboard box with pine pellets as bedding, a one gallon waterer, and we're feeding Dumore chick and duck feed from a plastic trough. It doesn't say it's medicated. We're using a 250 watt heat lamp and the temperature is between 90 and 95. They seemed very healthy, ate, drank water, slept, and ran around the brooding box all day yesterday. Everything seemed fine until last night when one separated from the others and seemed to sleep more. She died within hours. The rest seemed fine until this evening when another one died suddenly after doing the same thing. They are not kicking their feet when they die or arching their backs like I've read they do if they are dying of a viral infection. They just seem to get sleepy and weak, lay down, and then their heads fall over and they're gone. What can be causing this and what can we do to stop it?