Several months ago, I went into my coop to find one of my runners dead. Over the course of the next couple weeks I had others start to show disturbing symptoms, similar to botulism, but not as severe and it went away within a couple days with each duck. I had recently moved their poultry netting to a different area and it was a lot more boggy over there. I think there was something toxic that they got into.
Haven't had any issues after moving their fencing, and you can bet your boots I won't put their fencing over there again.
I'm very sorry to hear about your ducks. I don't blame you at all for crying. It can hurt a lot.
Glad that the rest of yours recovered. I looked up symptoms for botulism and don't believe that was what killed my runners. Toxicity is a possibility. I still don't know.
I obsessively count mine every time I go outside now, but the remaining eight seem to be fine.
I have to chime in - I lost several Runners (all ducks, of course) last year to what I believe to be cyanobacteria toxicity. There was a puddle that the Runners could access and they dabbled in it regularly. The conditions were hot and humid, and algae proliferated in the puddle. One morning, I found a dead duck in the coop. Soon after, several others became paralyzed and didn't recover, despite my efforts.
After researching the issue, I had gravel brought in to fill the depression and prevent water from pooling. There were no further losses, but the damage had been done.
Now, I look suspiciously at puddles around here in summer and will fill every one, if needed. There have been no recurrences since then, though.
Condolences to all who have lost ducks to blue-green algae poisoning or botulism. I know how difficult it can be.