Last Wednesday, I received my order from Metzers. All seven ducklings arrived healthy and well, and were eating and drinking within seconds of putting them in the brooder. Almost all of them had been growing exponentially, except the runner duck, who seemed to be remaining small and sleeping a lot. I figured that this was just because it's a smaller breed, but now I'm not so sure, because she died this morning. I really don't have a clue why she died. She was drinking and I think she was eating (although I'm not entirely sure). She was preening and playing with the other ducklings, right up until last night. During swim time, I noticed that she wasn't enjoying the water nearly as much as she had been previously (she wouldn't even try to swim. She just stood there in the shallow end while the others raced around her), so I took her out, dried her off, and put her back in the brooder. In the brooder, she pretty much collapsed, just laid down and started cleaning herself off--she was also trying to spread oil from her oil gland, but she did it all laying down. By the time I went to bed (around midnight), she seemed to be doing well again, and was up drinking. By the time my brother got up this morning (around 6:30), she was dead. She had also been breathing fine, with no wheezing or "panting". I don't know what could have killed my duckling. Does anybody have any ideas?