Started out with 6 call duck chicks that hatched the second week of August. The first one died in October, she was very small in comparison to the others. 2 weeks later, another died, no apparent cause. About 3 weeks after that another died again no apparent cause. Now one of the last 2 appear ill from the same thing as the others. Ducks appear fine and healthy then out of the blue they aren't eating and only drinking a little bit. They stop walking around like they are cold but they aren't, they have a heat lamp available and they use it. Their parents are very healthy. They were normal healthy hatches. They are secluded from all other animal and birds. Any help would be greatly appreciated.