Very sorry for your loss, they can sure hide their illness till right before death a lot of times. So unless you had a necropsy done you'll never know. Hopefully it was just something with her and the rest will be fine.
Your box you keep them in at night is it got good ventilation windows etc? Very important ducks have good fresh air flow where they sleep even in winter months.
I had one of my Runners get sick and die no idea either but what I did is I used some Oxine Ah and went in and sprayed the coop down real good before letting the rest in to sleep but you know they had all been around her all week that she was sick so I doubt my efforts did much, so far all of mine are doing fine and it's been a little over a week since she passed.
Other than just keeping a close eye on the others for now and making sure they have good feed and fresh water with ACV added it's a great tonic, clean bedding as possible Ammonia build up is another killer of poultry so another reason for good ventilation inside their houses.
Wish I could add more.
Please let us know how everyone is doing it may take them several days to get over their loss they form such a close bond with their flock.
Thank you for responding! Their night box does have good ventilation. We built it where the inside has a complete open area at the top. (Honestly, after construction, I was concerned if something got through the wire outside and in to the actual coop, they could easily get inside the night box and kill them all.) Also, I clean their enclosure every day with fresh pine shavings in the night box and fresh straw on the floor of their duck house as well. I don't clean out all the wet straw from where they drink water every day, is that bad? I clean all the wet straw around the waterer I'd guess every 3 day so. The only thing that I know all of them pecked at was a pool noodle. I discovered they had been pecking at them through the pallet where we keep them stored. I am not sure how long they had been doing it, but I removed them from the lower deck so they couldn't get to them anymore. That was over a week ago, I think.
The rest seem to be alright. One of them, that normally is so affectionate, pecked me and she has never done that before. I am crossing my fingers that the darn pool noodle doesn't kill them all.
