I started with 2 a month ago (we think they are rouens) and we just took in 2 new ones that the previous owner didn't want. Make sure you do your homework before you get ducklings!
I was very sad and confused. It was made worse that two of them came back all scared and disorganized at night and the third one is somewhere. I don't know if its even alive. I learned my lesson. I am not letting the remaining two out of my sight again. They will have to stay in their cages during the morning when I go to work... I will probably read something while they are spending their 3 hour free time before going back into the cage...